Subjects -> ASTRONOMY (Total: 94 journals)
Showing 1 - 46 of 46 Journals sorted alphabetically
Advances in Astronomy     Open Access   (Followers: 49)
Annual Review of Astronomy and Astrophysics     Full-text available via subscription   (Followers: 50)
Annual Review of Earth and Planetary Sciences     Full-text available via subscription   (Followers: 67)
Artificial Satellites     Open Access   (Followers: 21)
Astrobiology     Hybrid Journal   (Followers: 11)
Astronomical & Astrophysical Transactions: The Journal of the Eurasian Astronomical Society     Hybrid Journal   (Followers: 7)
Astronomical Review     Open Access   (Followers: 5)
Astronomische Nachrichten     Hybrid Journal   (Followers: 4)
Astronomy & Geophysics     Hybrid Journal   (Followers: 49)
Astronomy and Astrophysics     Full-text available via subscription   (Followers: 67)
Astronomy and Computing     Hybrid Journal   (Followers: 6)
Astronomy Letters     Hybrid Journal   (Followers: 22)
Astronomy Reports     Hybrid Journal   (Followers: 22)
Astronomy Studies Development     Open Access   (Followers: 15)
Astroparticle Physics     Hybrid Journal   (Followers: 10)
Astrophysical Bulletin     Hybrid Journal   (Followers: 4)
Astrophysics     Hybrid Journal   (Followers: 35)
Astrophysics and Space Science     Hybrid Journal   (Followers: 49)
Astrophysics and Space Sciences Transactions (ASTRA)     Open Access   (Followers: 60)
Astropolitics: The International Journal of Space Politics & Policy     Hybrid Journal   (Followers: 13)
Celestial Mechanics and Dynamical Astronomy     Hybrid Journal   (Followers: 15)
Chinese Astronomy and Astrophysics     Full-text available via subscription   (Followers: 25)
Colloid Journal     Hybrid Journal   (Followers: 2)
Comptes Rendus : Physique     Open Access   (Followers: 2)
Computational Astrophysics and Cosmology     Open Access   (Followers: 6)
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 143)
Earth, Moon, and Planets     Hybrid Journal   (Followers: 47)
Earth, Planets and Space     Open Access   (Followers: 77)
EAS Publications Series     Full-text available via subscription   (Followers: 8)
EPL Europhysics Letters     Partially Free   (Followers: 8)
Experimental Astronomy     Hybrid Journal   (Followers: 38)
Expert Opinion on Astronomy and Astrophysics     Open Access   (Followers: 8)
Extreme Life, Biospeology & Astrobiology - International Journal of the Bioflux Society     Full-text available via subscription   (Followers: 4)
Few-Body Systems     Hybrid Journal   (Followers: 1)
Foundations of Physics     Hybrid Journal   (Followers: 40)
Frontiers in Astronomy and Space Sciences     Open Access   (Followers: 15)
Galaxies     Open Access   (Followers: 6)
Globe, The     Full-text available via subscription   (Followers: 3)
Gravitation and Cosmology     Hybrid Journal   (Followers: 6)
Icarus     Hybrid Journal   (Followers: 71)
International Journal of Advanced Astronomy     Open Access   (Followers: 21)
International Journal of Astrobiology     Hybrid Journal   (Followers: 4)
International Journal of Astronomy     Open Access   (Followers: 22)
International Journal of Astronomy and Astrophysics     Open Access   (Followers: 36)
International Journal of Satellite Communications Policy and Management     Hybrid Journal   (Followers: 15)
International Letters of Chemistry, Physics and Astronomy     Open Access   (Followers: 8)
ISRN Astronomy and Astrophysics     Open Access   (Followers: 14)
Journal for the History of Astronomy     Full-text available via subscription   (Followers: 20)
Journal of Astrobiology & Outreach     Open Access   (Followers: 5)
Journal of Astronomical Instrumentation     Open Access   (Followers: 3)
Journal of Astrophysics     Open Access   (Followers: 33)
Journal of Astrophysics and Astronomy     Open Access   (Followers: 58)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 133)
Journal of Geophysical Research : Planets     Full-text available via subscription   (Followers: 116)
Journal of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 136)
Journal of High Energy Astrophysics     Full-text available via subscription   (Followers: 25)
Kinematics and Physics of Celestial Bodies     Hybrid Journal   (Followers: 11)
KronoScope     Hybrid Journal   (Followers: 1)
Macalester Journal of Physics and Astronomy     Open Access   (Followers: 5)
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 13)
Monthly Notices of the Royal Astronomical Society : Letters     Hybrid Journal   (Followers: 2)
Nature Astronomy     Hybrid Journal   (Followers: 14)
New Astronomy     Hybrid Journal   (Followers: 26)
New Astronomy Reviews     Full-text available via subscription   (Followers: 19)
Nonlinear Dynamics     Hybrid Journal   (Followers: 19)
NRIAG Journal of Astronomy and Geophysics     Open Access   (Followers: 4)
Physics of the Dark Universe     Open Access   (Followers: 4)
Planetary and Space Science     Hybrid Journal   (Followers: 106)
Planetary Science     Open Access   (Followers: 52)
Proceedings of the International Astronomical Union     Full-text available via subscription   (Followers: 2)
Publications of the Astronomical Society of Australia     Hybrid Journal   (Followers: 3)
Publications of the Astronomical Society of Japan     Hybrid Journal   (Followers: 4)
Research & Reviews : Journal of Space Science & Technology     Full-text available via subscription   (Followers: 20)
Research in Astronomy and Astrophysics     Full-text available via subscription   (Followers: 38)
Revista Mexicana de Astronomía y Astrofísica     Open Access   (Followers: 3)
Science China : Physics, Mechanics & Astronomy     Full-text available via subscription   (Followers: 4)
Science China Physics, Mechanics & Astronomy     Hybrid Journal   (Followers: 4)
Solar Physics     Hybrid Journal   (Followers: 29)
Solar System Research     Hybrid Journal   (Followers: 15)
Space Science International     Open Access   (Followers: 118)
Space Science Reviews     Hybrid Journal   (Followers: 92)
Space Weather     Full-text available via subscription   (Followers: 27)
Transport and Aerospace Engineering     Open Access   (Followers: 13)
Universe     Open Access   (Followers: 6)
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Number of Followers: 6  

  This is an Open Access Journal Open Access journal
ISSN (Online) 2075-4434
Published by MDPI Homepage  [84 journals]
  • Galaxies, Vol. 10, Pages 60: Breakthrough Multi-Messenger Astrophysics
           with the THESEUS Space Mission

    • Authors: Giulia Stratta, Lorenzo Amati, Marica Branchesi, Riccardo Ciolfi, Nial Tanvir, Enrico Bozzo, Diego Götz, Paul O’Brien, Andrea Santangelo
      First page: 60
      Abstract: The mission concept THESEUS (Transient High Energy Sky and Early Universe Surveyor) aims at exploiting Gamma-Ray Bursts (GRB) to explore the early Universe, as well as becoming a cornerstone of multi-messenger and time-domain astrophysics. To achieve these goals, a key feature is the capability to survey the soft X-ray transient sky and to detect the faint and soft GRB population so far poorly explored. Among the expected transients there will be high-redshift GRBs, nearby low-luminosity, X-ray Flashes and short GRBs. Our understanding of the physics governing the GRB prompt emission will benefit from the 0.3 keV–10 MeV simultaneous observations for an unprecedented large number of hundreds of events per year. In particular the mission will provide the identification, accurate sky localisation and characterization of electromagnetic counterparts to sources of gravitational wave and neutrino sources, which will be routinely detected during the 2030s by the upgraded second generation and third generation Gravitational Wave (GW) interferometers and next generation neutrino detectors.
      Citation: Galaxies
      PubDate: 2022-04-21
      DOI: 10.3390/galaxies10030060
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 61: Radio Galaxies at TeV Energies

    • Authors: Cameron Rulten
      First page: 61
      Abstract: Unlike blazars, radio galaxies have jets that are misaligned relative to our line-of-sight. This misaligned geometry provides us with a unique view of both the jet and super massive black hole. To date, four radio galaxies have been detected at TeV energies with an additional two active galactic nuclei shown to exhibit both radio galaxy and BL Lac-type properties. TeV observations of radio galaxies have revealed these objects to be fascinating, displaying ultra-fast variability and often relatively hard spectral energy distributions. This work aims to provide a review of the current state of radio galaxy observations within the context of very-high-energy γ-ray astronomy, while also highlighting that radio galaxies are excellent targets for multi-wavelength observations. A number of motivations for the continued study of radio galaxies are provided, and these are discussed with a focus on the key observational results, including implications for future observations with next-generation instruments soon to be operational.
      Citation: Galaxies
      PubDate: 2022-04-22
      DOI: 10.3390/galaxies10030061
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 62: Understanding High-Energy (UV and X-ray)
           Emission from AGB Stars—Episodic Accretion in Binary Systems

    • Authors: Raghvendra Sahai, Jorge Sanz-Forcada, Martin Guerrero, Roberto Ortiz, Carmen Sanchez Contreras
      First page: 62
      Abstract: X-ray surveys of UV-emitting AGB stars show that ∼40% of objects with FUV emission and GALEX FUV/NUV flux ratio Rfuv/nuv ∼> 0.2 (fuvAGB stars) have variable X-ray emission characterized by very high temperatures (Tx∼35–160 MK) and luminosities (Lx∼0.002–0.2 L⊙), indicating the presence of accretion associated with a close binary companion. However, the UV-emitting AGB star population is dominated by objects with Rfuv/nuv ≲ 0.06 (nuvAGB stars), and we do not know whether the UV emission from these is intrinsic to the AGB star or extrinsic (i.e., due to binarity). In order to help distinguish between intrinsic and extrinsic models of the puzzling high-energy emission of cool AGB stars, we report results from two studies—(i) XMM-Newton X-observations of two nuvAGB stars, and (ii) simple chromosphere modeling. In study (i), we detect the one which has the lower FUV/NUV ratio, with a total Lx = 0.00027 L⊙, and a spectrum best fitted with a dominant component at Tx∼10 MK, most likely coronal emission from a main-sequence companion. Therefore, a significant fraction of nuvAGB stars may also be binaries with active, but weak accretion. Study (ii) shows that chromospheres with temperatures of ∼10,000 K can produce Rfuv/nuv≲0.06; higher ratios require hotter gas, implying active accretion.
      Citation: Galaxies
      PubDate: 2022-04-25
      DOI: 10.3390/galaxies10030062
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 63: The Current Status and Future Prospects of
           KAGRA, the Large-Scale Cryogenic Gravitational Wave Telescope Built in the
           Kamioka Underground

    • Authors: Homare Abe, Tomotada Akutsu, Masaki Ando, Akito Araya, Naoki Aritomi, Hideki Asada, Yoichi Aso, Sangwook Bae, Rishabh Bajpai, Kipp Cannon, Zhoujian Cao, Eleonora Capocasa, Man Chan, Dan Chen, Yi-Ru Chen, Marc Eisenmann, Raffaele Flaminio, Heather Fong, Yuta Fujikawa, Yuya Fujimoto, I. Hadiputrawan, Sadakazu Haino, Wenbiao Han, Kazuhiro Hayama, Yoshiaki Himemoto, Naoatsu Hirata, Chiaki Hirose, Tsung-Chieh Ho, Bin-Hua Hsieh, He-Feng Hsieh, Chia-Hsuan Hsiung, Hsiang-Yu Huang, Panwei Huang, Yao-Chin Huang, Yun-Jing Huang, David Hui, Kohei Inayoshi, Yuki Inoue, Yousuke Itoh, Pil-Jong Jung, Takaaki Kajita, Masahiro Kamiizumi, Nobuyuki Kanda, Takashi Kato, Chunglee Kim, Jaewan Kim, Young-Min Kim, Yuichiro Kobayashi, Kazunori Kohri, Keiko Kokeyama, Albert Kong, Naoki Koyama, Chihiro Kozakai, Jun’ya Kume, Sachiko Kuroyanagi, Kyujin Kwak, Eunsub Lee, Hyung Lee, Ray-Kuang Lee, Matteo Leonardi, Kwan-Lok Li, Pengbo Li, Lupin Lin, Chun-Yu Lin, En-Tzu Lin, Hong-Lin Lin, Guo-Chin Liu, Ling-Wei Luo, Miftahul Ma’arif, Yuta Michimura, Norikatsu Mio, Osamu Miyakawa, Kouseki Miyo, Shinji Miyoki, Nozomi Morisue, Kouji Nakamura, Hiroyuki Nakano, Masayuki Nakano, Tatsuya Narikawa, Lan Quynh, Takumi Nishimoto, Atsushi Nishizawa, Yoshihisa Obayashi, Kwangmin Oh, Masatake Ohashi, Tomoya Ohashi, Masashi Ohkawa, Yoshihiro Okutani, Ken-ichi Oohara, Shoichi Oshino, Kuo-Chuan Pan, Alessandro Parisi, June Park, Fabián Arellano, Surojit Saha, Kazuki Sakai, Takahiro Sawada, Yuichiro Sekiguchi, Lijing Shao, Yutaka Shikano, Hirotaka Shimizu, Katsuhiko Shimode, Hisaaki Shinkai, Ayaka Shoda, Kentaro Somiya, Inhyeok Song, Ryosuke Sugimoto, Jishnu Suresh, Takamasa Suzuki, Takanori Suzuki, Toshikazu Suzuki, Hideyuki Tagoshi, Hirotaka Takahashi, Ryutaro Takahashi, Hiroki Takeda, Mei Takeda, Atsushi Taruya, Takayuki Tomaru, Tomonobu Tomura, Lucia Trozzo, Terrence Tsang, Satoshi Tsuchida, Takuya Tsutsui, Darkhan Tuyenbayev, Nami Uchikata, Takashi Uchiyama, Tomoyuki Uehara, Koh Ueno, Takafumi Ushiba, Maurice Putten, Tatsuki Washimi, Chien-Ming Wu, Hsun-Chung Wu, Tomohiro Yamada, Kazuhiro Yamamoto, Takahiro Yamamoto, Ryo Yamazaki, Shu-Wei Yeh, Jun’ichi Yokoyama, Takaaki Yokozawa, Hirotaka Yuzurihara, Simon Zeidler, Yuhang Zhao
      First page: 63
      Abstract: KAGRA is a gravitational-wave (GW) detector constructed in Japan with two unique key features: It was constructed underground, and the test-mass mirrors are cooled to cryogenic temperatures. These features are not included in other kilometer-scale detectors but will be adopted in future detectors such as the Einstein Telescope. KAGRA performed its first joint observation run with GEO600 in 2020. In this observation, the sensitivity of KAGRA to GWs was inferior to that of other kilometer-scale detectors such as LIGO and Virgo. However, further upgrades to the detector are ongoing to reach the sensitivity for detecting GWs in the next observation run, which is scheduled for 2022. In this article, the current situation, sensitivity, and future perspectives are reviewed.
      Citation: Galaxies
      PubDate: 2022-04-26
      DOI: 10.3390/galaxies10030063
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 64: Global Understanding of Accretion and
           Ejection around Black Holes

    • Authors: Santanu Mondal
      First page: 64
      Abstract: Accretion and ejection around compact objects, mainly around black holes, both in low mass, and supermassive, is rich and has been studied exhaustively [...]
      Citation: Galaxies
      PubDate: 2022-04-27
      DOI: 10.3390/galaxies10030064
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 65: Research Facilities for Europe’s Next
           Generation Gravitational-Wave Detector Einstein Telescope

    • Authors: Sibilla Di Pace, Valentina Mangano, Lorenzo Pierini, Amirsajjad Rezaei, Jan-Simon Hennig, Margot Hennig, Daniela Pascucci, Annalisa Allocca, Iara Tosta e Melo, Vishnu Nair, Philippe Orban, Ameer Sider, Shahar Shani-Kadmiel, Joris Van Heijningen
      First page: 65
      Abstract: The Einstein Telescope is Europe’s next generation gravitational-wave detector. To develop all necessary technology, four research facilities have emerged across Europe: The Amaldi Research Center (ARC) in Rome (Italy), ETpathfinder in Maastricht (The Netherlands), SarGrav in the Sos Enattos mines on Sardinia (Italy) and E-TEST in Liége (Belgium) and its surroundings. The ARC pursues the investigation of a large cryostat, equipped with dedicated low-vibration cooling lines, to test full-scale cryogenic payloads. The installation will be gradual and interlaced with the payload development. ETpathfinder aims to provide a low-noise facility that allows the testing of full interferometer configurations and the interplay of their subsystems in an ET-like environment. ETpathfinder will focus amongst others on cryogenic technologies, silicon mirrors, lasers and optics at 1550 and 2090 nm and advanced quantum noise reduction schemes. The SarGrav laboratory has a surface lab and an underground operation. On the surface, the Archimedes experiment investigates the interaction of vacuum fluctuations with gravity and is developing (tilt) sensor technology for the Einstein Telescope. In an underground laboratory, seismic characterisation campaigns are undertaken for the Sardinian site characterisation. Lastly, the Einstein Telecope Euregio meuse-rhine Site & Technology (E-TEST) is a single cryogenic suspension of an ET-sized silicon mirror. Additionally, E-TEST investigates the Belgian–Dutch–German border region that is the other candidate site for Einstein Telescope using boreholes and seismic arrays and hydrogeological characterisation. In this article, we describe the Einstein Telescope, the low-frequency part of its science case and the four research facilities.
      Citation: Galaxies
      PubDate: 2022-04-28
      DOI: 10.3390/galaxies10030065
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 66: Gamma-Ray Bursts Afterglow Physics and the
           VHE Domain

    • Authors: Davide Miceli, Lara Nava
      First page: 66
      Abstract: Afterglow radiation in gamma-ray bursts (GRB), extending from the radio band to GeV energies, is produced as a result of the interaction between the relativistic jet and the ambient medium. Although in general the origin of the emission is robustly identified as synchrotron radiation from the shock-accelerated electrons, many aspects remain poorly constrained, such as the role of inverse Compton emission, the particle acceleration mechanism, the properties of the environment and of the GRB jet itself. The extension of the afterglow emission into the TeV band has been discussed and theorized for years, but has eluded for a long time the observations. Recently, the Cherenkov telescopes, MAGIC and H.E.S.S., have unequivocally proven that afterglow radiation is also produced above 100 GeV, up to at least a few TeV. The accessibility of the TeV spectral window will largely improve with the upcoming facility CTA (the Cherenkov Telescope Array). In this review article, we first revise the current model for afterglow emission in GRBs, its limitations and open issues. Then, we describe the recent detections of very high energy emission from GRBs and the origin of this radiation. Implications on the understanding of afterglow radiation and constraints on the physics of the involved processes will be deeply investigated, demonstrating how future observations, especially by the CTA Observatory, are expected to give a key contribution in improving our comprehension of such elusive sources.
      Citation: Galaxies
      PubDate: 2022-05-05
      DOI: 10.3390/galaxies10030066
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 67: The Detection of GRBs at VHE: A Challenge
           Lasting for More than Two Decades, What Is Next'

    • Authors: Alessio Berti, Alessandro Carosi
      First page: 67
      Abstract: Unveiling the mystery of gamma-ray bursts (GRBs) has been the target of many multi-waveband observational and theoretical efforts during the last decades. The results collected by current and past space-based instruments have provided important insights into the mechanisms at the origin of their prompt and afterglow phases. On the other hand, many questions, such as the the origin of the multi-GeV signal observed in a large number of events, remained unanswered. Within this framework, the first firm detections of a very-high-energy (VHE, E≳100 GeV) emission component by MAGIC and H.E.S.S. collaborations represented an important, long-awaited result for the VHE astrophysics community. However, while such discoveries opened a new era in the study of GRBs, they also provided an unexpected complexity due to the differences between the phenomenology of the observed events. This revealed that we still have an incomplete comprehension of GRB physics. In the nearby future, observations by the Cherenkov Telescope Array Observatory (CTAO), with unprecedented sensitivity in the VHE band, will have a key role in the study of these enigmatic objects and their interactions with the surrounding environment. In this review we will cover the recent GRB history, highlighting the efforts of follow-up campaigns by the VHE community that led to the first VHE GRB detection, and outlining what we can expect from future facilities in the next decades.
      Citation: Galaxies
      PubDate: 2022-05-10
      DOI: 10.3390/galaxies10030067
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 68: Avoiding the Great Filter: Predicting the
           Timeline for Humanity to Reach Kardashev Type I Civilization

    • Authors: Jonathan H. Jiang, Fuyang Feng, Philip E. Rosen, Kristen A. Fahy, Prithwis Das, Piotr Obacz, Antong Zhang, Zong-Hong Zhu
      First page: 68
      Abstract: The level of technological development of any civilization can be gauged in large part by the amount of energy it produces for its use, but also encompasses that civilization’s stewardship of its home world. Following the Kardashev definition, a Type I civilization is able to store and use all the energy available on its planet. In this study, we develop a model based on Carl Sagan’s K formula, and use this model to analyze the consumption and energy supply of the three most important energy sources: fossil fuels (e.g., coal, oil, natural gas, crude, NGL, and feedstocks), nuclear energy, and renewable energy. We also consider environmental limitations suggested by the United Nations Framework Convention on Climate Change, the International Energy Agency, and those specific to our calculations, to predict when humanity will reach the level of a Kardashev Scale Type I civilization. Our findings suggest that the best estimate for our civilization to attain Type I status is within the common calendar year range of 2333 to 2404.
      Citation: Galaxies
      PubDate: 2022-05-12
      DOI: 10.3390/galaxies10030068
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 69: A Mass Dependent Density Profile from Dwarfs
           to Clusters

    • Authors: Antonino Del Popolo, Morgan Le Delliou
      First page: 69
      Abstract: In this paper, we extend the work of Freundlich et al. 2020 who showed how to obtain a Dekel–Zhao density profile with mass dependent shape parameters in the case of galaxies. In the case of Freundlich et al. 2020, the baryonic dependence was obtained using the NIHAO set of simulations. In our case, we used simulations based on a model of ours. Following Freundlich et al. 2020, we obtained the dependence from baryon physics of the two shape parameters, obtaining in this way a mass dependent Dekel–Zhao profile describing the dark matter profiles from galaxies to clusters of galaxies. The extension to the Dekel–Zhao mass dependent profile to clusters of galaxies is the main result of the paper. In the paper, we show how the Dekel–Zhao mass dependent profile gives a good description of the density profiles of galaxies, already shown by Freundlich et al. 2020, but also to a set of clusters of galaxies.
      Citation: Galaxies
      PubDate: 2022-05-18
      DOI: 10.3390/galaxies10030069
      Issue No: Vol. 10, No. 3 (2022)
  • Galaxies, Vol. 10, Pages 38: The GRB Prompt Emission: An Unsolved Puzzle

    • Authors: Željka Bošnjak, Rodolfo Barniol Duran, Asaf Pe’er
      First page: 38
      Abstract: The recent multi-messenger and multi-wavelength observations of gamma-ray bursts (GRBs) have encouraged renewed interest in these energetic events. In spite of the substantial amount of data accumulated during the past few decades, the nature of the prompt emission remains an unsolved puzzle. We present an overview of the leading models for their prompt emission phase, focusing on the perspective opened by future missions.
      Citation: Galaxies
      PubDate: 2022-02-22
      DOI: 10.3390/galaxies10020038
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 39: Gamma-Ray Cosmology and Tests of Fundamental

    • Authors: Jonathan Biteau, Manuel Meyer
      First page: 39
      Abstract: The propagation of gamma-rays over cosmological distances is the subject of extensive theoretical and observational research at GeV and TeV energies. The mean free path of gamma-rays in the cosmic web is limited above 100 GeV due to the production of electrons and positrons on the cosmic optical and infrared backgrounds. Electrons and positrons cool in the intergalactic medium while gyrating in its magnetic fields, which could cause either its global heating or the production of lower-energy secondary gamma-rays. The energy distribution of gamma-rays surviving the cosmological journey carries observed absorption features that gauge the emissivity of baryonic matter over cosmic time, constrain the distance scale of ΛCDM cosmology, and limit the alterations of the interaction cross section. Competitive constraints are, in particular, placed on the cosmic star-formation history as well as on phenomena expected from quantum gravity and string theory, such as the coupling to hypothetical axion-like particles or the violation of Lorentz invariance. Recent theoretical and observational advances offer a glimpse of the multi-wavelength and multi-messenger path that the new generation of gamma-ray observatories is about to open.
      Citation: Galaxies
      PubDate: 2022-02-22
      DOI: 10.3390/galaxies10020039
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 40: Cylindrical Gravastar Like-Structures in f(G)

    • Authors: M. Z. Bhatti, Z. Yousaf, A. Rehman
      First page: 40
      Abstract: The aim of this manuscript is to explore singularity-free solution for a specific self-gravitating highly dense object known as gravastar suggested by Mazur and Mottola, in the context of f(G) gravity theory. Gravastars are regarded as a possible alternate to black hole. To derive modified field equations and law of conservation related to Gauss-Bonnet gravity, we assume cylindrically symmetric irrotational configuration. Particular equation of states are used for the illustration of three sectors of gravastar model. Furthermore, we are intended to obtain a regular solution for our model and graphs will be used to elaborate various substantial characteristics of it.
      Citation: Galaxies
      PubDate: 2022-02-23
      DOI: 10.3390/galaxies10020040
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 41: Follow-Up of Extended Shells around B[e]

    • Authors: Tiina Liimets, Michaela Kraus, Alexei Moiseev, Nicolas Duronea, Lydia Sonia Cidale, Cecilia Fariña
      First page: 41
      Abstract: B[e] stars are massive B type emission line stars in different evolutionary stages ranging from pre-main sequence to post-main sequence. Due to their mass loss and ejection events these objects deposit huge amounts of mass and energy into their environment and enrich it with chemically processed material, contributing significantly to the chemical and dynamical evolution of their host galaxies. However, the large-scale environments of these enigmatic objects have not attracted much attention. The first and so far only catalog reporting the detection of extended shells around a sample of B[e] stars was an Hα imaging survey carried out in the year 2001, and was limited to bright targets in the northern hemisphere. We have recently started a follow-up of those targets to detect possible evolution of their nebulae in the plane of the sky over a baseline of two decades. Furthermore, we extend our survey to southern targets and fainter northern ones to complement and complete our knowledge on large-scale ejecta surrounding B[e] stars. Besides imaging in Hα and selected nebular lines, we utilize long-slit and 3D spectral observations across the nebulae to derive their physical properties. We discovered pronounced nebula structures around 15 more objects, resulting in a total of 27 B[e] stars with a large-scale nebula. Here we present our (preliminary) results for three selected objects: the two massive supergiants MWC137 and MWC 314, and the unclassified B[e] star MWC 819.
      Citation: Galaxies
      PubDate: 2022-03-01
      DOI: 10.3390/galaxies10020041
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 42: Toward Calibration of the Global Network of
           Gravitational Wave Detectors with Sub-Percent Absolute and Relative

    • Authors: Sudarshan Karki, Dripta Bhattacharjee, Richard L. Savage
      First page: 42
      Abstract: The detection of gravitational-wave signals by the LIGO and Virgo observatories during the past few years has ushered us into the era of gravitational-wave astronomy, shifting our focus from detection to source parameter estimation. This has imposed stringent requirements on calibration in order to maximize the astrophysical information extracted from these detected signals. Current detectors rely on photon radiation pressure from auxiliary lasers to achieve required calibration accuracy. These photon calibrators have made significant improvements over the last few years, realizing fiducials displacements with sub-percent accuracy. This achieved accuracy is directly dependent on the laser power calibration. For the next observing campaign, scheduled to begin at the end of 2022, a new scheme is being implemented to achieve improved laser power calibration accuracy for all of the GW detectors in the global network. It is expected to significantly improve absolute and relative calibration accuracy for the entire network.
      Citation: Galaxies
      PubDate: 2022-03-05
      DOI: 10.3390/galaxies10020042
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 43: The Accreting White Dwarfs in Cataclysmic

    • Authors: Edward M. Sion, Patrick Godon
      First page: 43
      Abstract: Accreting white dwarfs (WDs) in cataclysmic variables (CVs) provide crucial insights about the accretion of mass and angular momentum in all types of binaries, including accreting NSs and BHs. Accreting WDs are the critical component in the single degenerate pathway to SNe Ia, along with the double degenerate merger pathway, they are the standard candles of cosmology proving that the universe is accelerating and the existence of dark energy. Another key question is whether the WD in a CV can grow in mass despite the mass loss due to thousands of nova explosions in its lifetime. Angular momentum loss drives CV evolution and accreting WDs offer critically needed WD masses from Gaia distances and reliable surface temperatures to derive the most accurate accretion rates. We review the studies on accreting WDs, including WD masses, accurate rotational velocities and chemical abundances of elements. Most of the progress that has been made is based upon Hubble Space Telescope spectroscopy and FUSE spectroscopy in the UV spectral region during dwarf nova quiescence and the low states of novalike variables, when the accreting WD dominates the UV spectral range.
      Citation: Galaxies
      PubDate: 2022-03-07
      DOI: 10.3390/galaxies10020043
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 44: Further Studies of the Association of
           Planetary Nebula BMP J16135406 with Galactic Open Cluster NGC 6067

    • Authors: Vasiliki Fragkou, Quentin A. Parker, Albert A. Zijlstra, Lisa Crause, Laurence Sabin, Roberto Vázquez
      First page: 44
      Abstract: Planetary Nebulae (PNe) that are physical members of Galactic open clusters are powerful probes that allow precise determination of their distance and crucially their initial mass on the main sequence. Here, we revisit the physical association of the PN BMP J1613–5406 with the open cluster NGC 6067 and present our preliminary results based on our new ESO/VLT FORS2 data. Our PN spectral data permit the calculation of a precise radial velocity and reddening to the PN that shows a tight consistency with the literature corresponding cluster parameters including importantly the radial velocity. Our measurements, combined with the agreement between the distances of the two objects and the fact that the PN is located well within the cluster boundaries, confirm that the PN is physically associated with the cluster. The cluster has a turn-off mass of around 5 solar masses that indicates a PN initial mass of around 5.6 solar masses. This is closer to the theoretical lower limit of core-collapse supernova formation than has ever been previously observed, providing a unique opportunity for further stellar and Galactic chemical evolution studies using this system.
      Citation: Galaxies
      PubDate: 2022-03-07
      DOI: 10.3390/galaxies10020044
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 45: Morphologies of Wolf–Rayet Planetary
           Nebulae Based on IFU Observations

    • Authors: Ashkbiz Danehkar
      First page: 45
      Abstract: Integral field unit (IFU) spectroscopy of planetary nebulae (PNe) provides a plethora of information about their morphologies and ionization structures. An IFU survey of a sample of PNe around hydrogen-deficient stars has been conducted with the Wide Field Spectrograph (WiFeS) on the ANU 2.3-m telescope. In this paper, we present the Hα kinematic observations of the PN M 2-42 with a weak emission-line star (wels), and the compact PNe Hen 3-1333 and Hen 2-113 around Wolf–Rayet ([WR]) stars from this WiFeS survey. We see that the ring and point-symmetric knots previously identified in the velocity [N ii] channels of M 2-42 are also surrounded by a thin exterior ionized Hα halo, whose polar expansion is apparently faster than the low-ionization knots. The velocity-resolved Hα channel maps of Hen 3-1333 and Hen 2-113 also suggest that the faint multipolar lobes may get to a projected outflow velocity of ∼100 ± 20 km s−1 far from the central stars. Our recent kinematic studies of the WiFeS/IFU survey of other PNe around [WR] and wels mostly hint at elliptical morphologies, while collimated outflows are present in many of them. As the WiFeS does not have adequate resolution for compact (≤6 arcsec) PNe, future high-resolution spatially-resolved observations are necessary to unveil full details of their morpho-kinematic structures.
      Citation: Galaxies
      PubDate: 2022-03-08
      DOI: 10.3390/galaxies10020045
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 46: Squeezing in Gravitational Wave Detectors

    • Authors: Sheila E. Dwyer, Georgia L. Mansell, Lee McCuller
      First page: 46
      Abstract: Injecting optical squeezed states of light, a technique known as squeezing, is now a tool for gravitational wave detection. Its ability to reduce quantum noise is helping to reveal more gravitational wave transients, expanding the catalog of observations in the last observing run. This review introduces squeezing and its history in the context of gravitational-wave detectors. It overviews the benefits, limitations and methods of incorporating squeezing into advanced interferometers, emphasizing the most relevant details for astrophysics instrumentation.
      Citation: Galaxies
      PubDate: 2022-03-09
      DOI: 10.3390/galaxies10020046
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 47: M 1–92 Revisited: New Findings and Open
           Questions: New NOEMA Observations of Minkowski’s Footprint

    • Authors: Javier Alcolea, Marcelino Agúndez, Valentín Bujarrabal, Arancha Castro-Carrizo, Jean-François Desmurs, John-Eduard Martínez-Fernández, Carmen Sánchez Contreras, Miguel Santander-García
      First page: 47
      Abstract: PN M 1–92, also known as Minkowski’s Footprint, is a textbook example of a massive pre-planetary nebula. It presents all the characteristics of this type of source: non-spherical symmetry (bipolar cylindrical symmetry in this case), high-velocity gas emission, large amounts of linear momentum and kinetic energy (momentum excess), and a self-similar growing structure. We have revisited this object by performing new NOEMA observations (with half arc-second resolution) of a wealth of molecules, including the rare isotopologues of CO, as well as other less abundant species. These maps provide new insights into the origin of this source. Our findings include the discovery of molecular species in the ionised regions of the nebula, confirming its shocked origin; the structure of the massive equatorial component, including the presence of active wind collisions; and the strong evidence that the AGB evolution of the source was terminated prematurely, probably due to the huge mass loss event that resulted in the formation/acceleration of the present nebula.
      Citation: Galaxies
      PubDate: 2022-03-10
      DOI: 10.3390/galaxies10020047
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 48: Millimetre Observations of Maser-Emitting
           Planetary Nebulae

    • Authors: Lucero Uscanga, José R. Rizzo, Miguel Santander-García, José F. Gómez, Luis F. Miranda, Olga Suárez, Panayotis Boumis, Mónica I. Rodríguez, Gerardo Ramos-Larios, Roldán A. Cala
      First page: 48
      Abstract: Observations in the millimetre bands of maser-emitting planetary nebulae (PNe) are crucial to study their circumstellar molecular gas at the beginning of the PN phase. Maser-emitting PNe are in the earliest phases of PN formation; therefore, these sources are key objects to study the molecular content during the early evolution of PNe. These circumstellar envelopes are active sites for the formation of molecules. We present preliminary results of millimetre observations with the IRAM 30 m telescope towards one PN (IRAS 17393−2727) of a sample of five maser-emitting PNe, where we detect 12CO and 13CO lines in both J=1→0 and J=2→1 transitions.
      Citation: Galaxies
      PubDate: 2022-03-11
      DOI: 10.3390/galaxies10020048
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 49: Weyl Conformal Symmetry Model of the Dark
           Galactic Halo

    • Authors: R. K. Nesbet
      First page: 49
      Abstract: The postulate of universal conformal (local Weyl scaling) symmetry modifies both general relativity and the Higgs scalar field model. The conformal Higgs model (CHM) generates an effective cosmological constant that fits the observed accelerating Hubble expansion for redshifts z≤1 (7.33 Gyr) accurately with only one free parameter. Growth of a galaxy is modeled by the central accumulation of matter from an enclosing empty spherical halo whose radius expands with depletion. Details of this process account for the nonclassical, radial centripetal acceleration observed at excessive orbital velocities in galactic haloes. There is no need for dark matter.
      Citation: Galaxies
      PubDate: 2022-03-15
      DOI: 10.3390/galaxies10020049
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 50: The Quantum Gravity Connection between
           Inflation and Quintessence

    • Authors: Christof Wetterich
      First page: 50
      Abstract: Inflation and quintessence can both be described by a single scalar field. The cosmic time evolution of this cosmon field realizes a crossover from the region of an ultraviolet fixed point in the infinite past to an infrared fixed point in the infinite future. This amounts to a transition from early inflation to late dynamical dark energy, with intermediate radiation and matter domination. The scaling solution of the renormalization flow in quantum gravity connects the two fixed points. It provides for the essential characteristics of the scalar potential needed for the crossover cosmology and solves the cosmological constant problem dynamically. The quantum scale symmetry at the infrared fixed point protects the tiny mass of the cosmon and suppresses the cosmon coupling to atoms without the need of a non-linear screening mechanism, thereby explaining apparent issues of fine tuning. For a given content of particles, the scaling solution of quantum gravity is a predictive framework for the properties of inflation and dynamical dark energy.
      Citation: Galaxies
      PubDate: 2022-03-17
      DOI: 10.3390/galaxies10020050
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 51: What Is Needed of a Scalar Field If It Is to
           Unify Inflation and Late Time Acceleration'

    • Authors: Nur Jaman, Mohammad Sami
      First page: 51
      Abstract: Quintessential inflation refers to scenarios in which a single scalar field is used to describe inflation and late time acceleration. This review is dedicated to the framework of quintessential inflation, with a focus on the building blocks of formalism. Consistent unification of inflation and late time acceleration using a single scalar field asks for a shallow field potential initially followed by steep behaviour thereafter and shallow again around the present epoch. The requirement of non-interference of the scalar field with thermal history dictates the steep nature of potential in the post-inflationary era, with a further restriction that late time physics be independent of initial conditions. We describe, in detail, the scaling and asymptotic scaling solutions and the mechanism of exit from the scaling regime to late time acceleration. The review includes a fresh look at scaling solutions that are central to the theme of unification of inflation and late time acceleration. As for the exit mechanism, special attention is paid to the coupling of massive neutrino matter to the scalar field, which builds up dynamically and can give rise to late time acceleration. We present a detailed analytical treatment of scalar field dynamics in the presence of coupling. We briefly discuss the distinguishing feature of quintessential inflation, namely the blue spectrum of gravity waves produced during the transition from inflation to the kinetic regime.
      Citation: Galaxies
      PubDate: 2022-03-23
      DOI: 10.3390/galaxies10020051
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 52: Why Masses of Binary Black Hole Mergers Are

    • Authors: Michal Křížek, Lawrence Somer
      First page: 52
      Abstract: We show that masses of binary black hole mergers are overestimated, since a large gravitational redshift is not taken into account. Such a phenomenon occurs due to time dilation in a close neighborhood of any black hole. This fact allows us to explain a high mass gap between observed binary neutron stars and calculated binary black hole mergers. We also present other reasons why masses of black hole mergers are determined incorrectly.
      Citation: Galaxies
      PubDate: 2022-03-23
      DOI: 10.3390/galaxies10020052
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 53: Cylindrical Planetary Nebulae. I. Flow from
           an Irradiated Ring

    • Authors: Vincent Icke
      First page: 53
      Abstract: Many bipolar nebulae with a pronounced cylindrical shape, such as Henize 3-401, show no indication whatsoever of interaction between a disk and a stellar wind, or a jet on the nebular axis. I propose that the disk that is observed at the base of the bipolar is itself the source of the outflow. In particular, I assume that irradiation from the central star causes the disk to evaporate. I have performed numerical hydrodynamical calculations of outflows driven by evaporation of a pseudo-barotropic ring around a hot central star. The first results show that the outflow shapes are cylindrical, and the internal structures are similar to what is observed in some of these nebulae. Since shape is only the first step in the assessment of a model, synthetic observations should be made. For the moment I merely verify that the scalar quantities observed in the archetypical cylindrical nebula Hen 3-401 can be accommodated in my models.
      Citation: Galaxies
      PubDate: 2022-03-24
      DOI: 10.3390/galaxies10020053
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 54: Isolating an Outflow Component in
           Single-Epoch Spectra of Quasars

    • Authors: Paola Marziani, Alice Deconto-Machado, Ascension Del Olmo
      First page: 54
      Abstract: Gaseous outflows appear to be a universal property of type-1 and type-2 active galactic nuclei (AGN). The main diagnostic is provided by emission features shifted to higher frequencies via the Doppler effect, implying that the emitting gas is moving toward the observer. However, beyond the presence of blueshift, the observational signatures of the outflows are often unclear, and no established criteria exist to isolate the outflow contribution in the integrated, single-epoch spectra of type-1 AGN. The emission spectrum collected the typical apertures of long-slit spectroscopy or of fiber optics sample contributions over a broad range of spatial scales, making it difficult to analyze the line profiles in terms of different kinematical components. Nevertheless, hundred of thousands of quasars spectra collected at moderate resolution demand a proper analysis of the line profiles for proper dynamical modeling of the emitting regions. In this small contribution, we analyze several profiles of the Hi Balmer line Hβ from composite and individual spectra of sources radiating at moderate Eddington ratio (Population B). Features and profile shapes that might be traced to outflow due to narrow-line region gas are detected over a wide range of luminosity.
      Citation: Galaxies
      PubDate: 2022-03-24
      DOI: 10.3390/galaxies10020054
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 55: A Beacon in the Galaxy: Updated Arecibo
           Message for Potential FAST and SETI Projects

    • Authors: Jonathan H. Jiang, Hanjie Li, Matthew Chong, Qitian Jin, Philip E. Rosen, Xiaoming Jiang, Kristen A. Fahy, Stuart F. Taylor, Zhihui Kong, Jamilah Hah, Zong-Hong Zhu
      First page: 55
      Abstract: An updated, binary-coded message has been developed for transmission to extraterrestrial intelligences in the Milky Way galaxy. The proposed message includes basic mathematical and physical concepts to establish a universal means of communication followed by information on the biochemical composition of life on Earth, the Solar System’s time-stamped position in the Milky Way relative to known globular clusters, as well as digitized depictions of the Solar System, and Earth’s surface. The message concludes with digitized images of the human form, along with an invitation for any receiving intelligences to respond. Calculation of the optimal timing during a given calendar year is specified for potential future transmission from both the Five-hundred-meter Aperture Spherical radio Telescope in China and the SETI Institute’s Allen Telescope Array in northern California to a selected region of the Milky Way which has been proposed as the most likely location for life to have developed. These powerful new beacons, the successors to the Arecibo radio telescope which transmitted the 1974 message upon which this expanded communication is in part based, can carry forward Arecibo’s legacy into the 21st century with this equally well-constructed communication from Earth’s technological civilization.
      Citation: Galaxies
      PubDate: 2022-03-25
      DOI: 10.3390/galaxies10020055
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 56: A Study of the Dusty Disks and Shells around
           Post-RGB Stars in the LMC

    • Authors: Geetanjali Sarkar, Raghvendra Sahai
      First page: 56
      Abstract: A new class of dusty post-Red Giant Branch (post-RGB) stars has recently been identified in the Magellanic Clouds. Their spectral energy distributions (SEDs) suggest that their mass-ejecta are similar to dusty post-Asymptotic Giant Branch (post-AGB) stars. We modeled the SEDs of a select sample of post-RGB and post-AGB stars in the Large Magellanic Cloud (LMC), quantified the total dust mass in the disks and shells and set rough constraints on the dust grain compositions and sizes. The shells were significantly more massive than the disks. Our models suggest that circumstellar disks, when present, are geometrically thick with a substantial opening angle, which is consistent with numerical simulations of CE evolution (CEE). Comparison of our model dust mass values with the predictions of dust production during CEE on the RGB suggest that CEE occurred near or at the tip of the RGB for the post-RGB sources in our sample. Amorphous silicate emission features at 10 and 18 μm are seen in the model spectra of several post-RGBs. A surprising result is that the ejected dust in certain post-RGB sources appears to be carbon-rich, thus, providing independent support for the hypothesis of binary interactions leading to the formation of dusty post-RGB objects.
      Citation: Galaxies
      PubDate: 2022-04-02
      DOI: 10.3390/galaxies10020056
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 57: Modelling Quintessential Inflation in
           Palatini-Modified Gravity

    • Authors: Konstantinos Dimopoulos, Alexandros Karam, López, Eemeli Tomberg
      First page: 57
      Abstract: We study a model of quintessential inflation constructed in R2-modified gravity with a non-minimally coupled scalar field, in the Palatini formalism. Our non-minimal inflaton field is characterised by a simple exponential potential. We find that successful quintessential inflation can be achieved with no fine-tuning of the model parameters. Predictions of the characteristics of dark energy will be tested by observations in the near future, while contrasting with existing observations provides insights on the modified gravity background, such as the value of the non-minimal coupling and its running.
      Citation: Galaxies
      PubDate: 2022-04-05
      DOI: 10.3390/galaxies10020057
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 58: Dynamics and Kinematics of the EUV Wave Event
           on 6 May 2019

    • Authors: Ramesh Chandra, P. F. Chen, Pooja Devi, Reetika Joshi, Y. W. Ni
      First page: 58
      Abstract: We present here the kinematics of the EUV wave associated with a GOES M1.0-class solar flare, which originates in NOAA AR 12740. The event is thoroughly observed with Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO) with high spatio-temporal resolutions. This event displays many features of EUV waves, which are very decisive for the understanding of the nature of EUV waves. These features include: a fast-mode wave, a pseudo wave, a slow-mode wave and stationary fronts, probably due to mode conversion. One fast-mode wave also propagates towards the coronal hole situated close to the north pole and the wave speed does not change when it encounters the coronal hole. We intend to provide self-consistent interpretations for all these different features.
      Citation: Galaxies
      PubDate: 2022-04-10
      DOI: 10.3390/galaxies10020058
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 59: On the VHE Spectrum and Formation of the
           Teraelectronvolt Pulsed Emission of the Crab Pulsar

    • Authors: Nino Chkheidze
      First page: 59
      Abstract: In the present paper, a model for the pulsed γ-ray emission of the Crab pulsar from 0.01 GeV to 1 TeV in the context of synchrotron emission generated in the vicinity of a light cylinder is developed. The generation of such high energies through the synchrotron process requires the existence of very energetic plasma particles in pulsar magnetospheres. It is assumed that the emitting particles are ultra-relativistic primary beam electrons re-accelerated to very high energies due to the Landau damping process of a special type of parametrically driven Langmuir waves. This type of Langmuir wave carries energy released through the rotational slow-down of a pulsar and is very effective in supplying the resonant particles with energy from a natural reservoir. The model provides simultaneous generation of energetic γ-ray and low-frequency radio (0.1–1 GHz) emission in the same location of the pulsar magnetosphere. These two radiations processes are triggered by a single plasma process, namely excitation of the cyclotron instability. This provides a natural explanation for the observed coincidence of radio and γ-ray signals observed from the Crab pulsar.
      Citation: Galaxies
      PubDate: 2022-04-12
      DOI: 10.3390/galaxies10020059
      Issue No: Vol. 10, No. 2 (2022)
  • Galaxies, Vol. 10, Pages 6: Non-Thermal Emission from Radio-Loud AGN Jets:
           Radio vs. X-rays

    • Authors: Elena Fedorova, Bohdan Hnatyk, Antonino Del Popolo, Anatoliy Vasylenko, Vadym Voitsekhovskyi
      First page: 6
      Abstract: We consider the sample of 55 blazars and Seyferts cross-correlated from the Planck all-sky survey based on the Early Release Compact Source Catalog (ERCSC) and Swift BAT 105-Month Hard X-ray Survey. The radio Planck spectra vs. X-ray Swift/XRT+BAT spectra of the active galactic nuclei (AGN) sample were fitted with the simple and broken power law (for the X-ray spectra taking into account also the Galactic neutral absorption) to test the dependencies between the photon indices of synchrotron emission (in radio range) and synchrotron self-Compton (SSC) or inverse-Compton emission (in X-rays). We show that for the major part of the AGN in our sample there is a correspondence between synchrotron and SSC photon indices (one of two for broken power-law model) compatible within the error levels. For such objects, this can give a good perspective for the task of distinguishing between the jet base counterpart from that one emitted in the disk+corona AGN “central engine”.
      Citation: Galaxies
      PubDate: 2022-01-04
      DOI: 10.3390/galaxies10010006
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 7: Gamma-Ray Bursts at TeV Energies:
           Observational Status

    • Authors: Koji Noda, Robert Daniel Parsons
      First page: 7
      Abstract: Gamma-ray bursts (GRBs) are some of the most energetic events in the Universe and are potential sites of cosmic ray acceleration up to the highest energies. GRBs have therefore been a target of interest for very high energy gamma-ray observatories for many years, leading to the recent discovery of a number of bursts with photons reaching energies above 100 GeV. We summarize the GRB observational campaigns of the current generation of very high energy gamma-ray observatories as well as describing the observations and properties of the GRBs discovered so far. We compare the properties of the very high energy bursts to the total GRB distribution and make predictions for the next generation of very high energy gamma-ray observations.
      Citation: Galaxies
      PubDate: 2022-01-05
      DOI: 10.3390/galaxies10010007
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 8: Mass Ratio and Spot Parameter Estimation from
           Eclipsing Binary Star Light Curves

    • Authors: Dirk Terrell
      First page: 8
      Abstract: Eclipsing binary stars have a rich history of contributing to the field of stellar astrophysics. Most of the available information on the fundamental properties of stars has come from the analysis of observations of binaries. The availability of powerful computers and sophisticated codes that apply physical models has resulted in determinations of masses and radii of sufficient accuracy to provide critical tests of theories of stellar structure and evolution. Despite their sophistication, these codes still require the guiding hand of trained scientists to extract reliable information. The computer code will produce results, but it is still imperative for the analyst to ensure that those results make astrophysical sense, and to ascertain their reliability. Care must be taken to ensure that we are asking the codes for parameters for which there is information in the data. The analysis of synthetic observations with simulated observational errors of typical size can provide valuable insight to the analysis process because the parameters used to generate the observations are known. Such observations are herein analyzed to guide the process of determining mass ratios and spot parameters from eclipsing binary light curves. The goal of this paper is to illustrate some of the subtleties that need to be recognized and treated properly when analyzing binary star data.
      Citation: Galaxies
      PubDate: 2022-01-05
      DOI: 10.3390/galaxies10010008
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 9: Eclipsing Binaries in Dynamically Interacting
           Close, Multiple Systems

    • Authors: Tamás Borkovits
      First page: 9
      Abstract: Close, compact, hierarchical, and multiple stellar systems, i.e., multiples having an outer orbital period from months to a few years, comprise a small but continuously growing group of the triple and multiple star zoo. Many of them consist of at least one eclipsing pair of stars and, therefore, exhibit readily observable short-term dynamical interactions among the components. Thus, their dynamical and astrophysical properties can be explored with high precision. In this paper we present an overview of the history of the search for additional components around eclipsing binaries from the first serendipitous discoveries to more systematic recent studies. We describe the different observational detection methods and discuss their connections to the different kinds of astrophysical and dynamical information that can be mined from different datasets. Moreover, the connection amongst the observable phenomena and the long-term dynamics of such systems is also discussed.
      Citation: Galaxies
      PubDate: 2022-01-06
      DOI: 10.3390/galaxies10010009
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 10: On the Polarisation of Radio Relics

    • Authors: Matthias Hoeft, Kamlesh Rajpurohit, Denis Wittor, Gabriella di Gennaro, Paola Domínguez-Fernández
      First page: 10
      Abstract: Radio relics are extended radio emission features which trace shock waves in the periphery of galaxy clusters originating from cluster mergers. Some radio relics show a highly polarised emission, which make relics an excellent probe for the magnetisation of the intra-cluster medium. The origin of the relic polarisation is still debated. It could be a result of tangentially stretching the magnetic field at the shock surface. This scenario would naturally explain the alignment of the polarisation (E-vectors) with the shock normal. We have implemented a toy model for the relic polarisation according to this scenario. We find that the magnetic field strength itself crucially affects the fractional polarisation. Moreover, we find that the shock strength has surprisingly little effect on the overall polarisation fraction. Finally, we find that the fractional polarisation may decrease downstream depending on the magnetic field strength. Our results demonstrates that the shock compression scenario provides a very plausible explanation for the radio relic polarisation which specific features permitting to test the origin of radio relic polarisation.
      Citation: Galaxies
      PubDate: 2022-01-10
      DOI: 10.3390/galaxies10010010
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 11: The Interstellar Medium of Dwarf Galaxies

    • Authors: Christian Henkel, Leslie K. Hunt, Yuri I. Izotov
      First page: 11
      Abstract: Dwarf galaxies are by far the most numerous galaxies in the Universe, showing properties that are quite different from those of their larger and more luminous cousins. This review focuses on the physical and chemical properties of the interstellar medium of those dwarfs that are known to host significant amounts of gas and dust. The neutral and ionized gas components and the impact of the dust will be discussed, as well as first indications for the existence of active nuclei in these sources. Cosmological implications are also addressed, considering the primordial helium abundance and the similarity of local Green Pea galaxies with young, sometimes protogalactic sources in the early Universe.
      Citation: Galaxies
      PubDate: 2022-01-12
      DOI: 10.3390/galaxies10010011
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 12: Detector Characterization and Mitigation of
           Noise in Ground-Based Gravitational-Wave Interferometers

    • Authors: Derek Davis, Marissa Walker
      First page: 12
      Abstract: Since the early stages of operation of ground-based gravitational-wave interferometers, careful monitoring of these detectors has been an important component of their successful operation and observations. Characterization of gravitational-wave detectors blends computational and instrumental methods of investigating the detector performance. These efforts focus both on identifying ways to improve detector sensitivity for future observations and understand the non-idealized features in data that has already been recorded. Alongside a focus on the detectors themselves, detector characterization includes careful studies of how astrophysical analyses are affected by different data quality issues. This article presents an overview of the multifaceted aspects of the characterization of interferometric gravitational-wave detectors, including investigations of instrumental performance, characterization of interferometer data quality, and the identification and mitigation of data quality issues that impact analysis of gravitational-wave events. Looking forward, we discuss efforts to adapt current detector characterization methods to meet the changing needs of gravitational-wave astronomy.
      Citation: Galaxies
      PubDate: 2022-01-14
      DOI: 10.3390/galaxies10010012
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 13: Lorentz Violation in Astroparticles and
           Gravitational Waves

    • Authors: Marco Schreck
      First page: 13
      Abstract: Lorentz invariance is one of the fundamental continuous symmetries of the laws of nature [...]
      Citation: Galaxies
      PubDate: 2022-01-17
      DOI: 10.3390/galaxies10010013
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 14: Dark Matter Effects on the Compact Star

    • Authors: H. C. Das, Ankit Kumar, Bharat Kumar, Suresh Kumar Patra
      First page: 14
      Abstract: The neutron star properties are generally determined by the equation of state of β-equilibrated dense matter. In this work, we consider the interaction of fermionic dark matter (DM) particles with nucleons via Higgs exchange and investigate the effect on the neutron star properties with the relativistic mean-field model equation of state coupled with DM. We deduce that DM significantly affects the neutron star properties, such as considerably reducing the maximum mass of the star, which depends on the percentage of the DM considered inside the neutron star. The tidal Love numbers both for electric and magnetic cases and surficial Love numbers are also studied for DM admixed NS. We observed that the magnitude of tidal and surficial Love numbers increases with a greater DM percentage. Further, we present post-Newtonian tidal corrections to gravitational waves decreased by increasing the DM percentage. The DM effect on the GW signal is significant during the late inspiral and merger stages of binary evolution for GW frequencies >500 Hz.
      Citation: Galaxies
      PubDate: 2022-01-18
      DOI: 10.3390/galaxies10010014
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 15: Accretion Disks and Long Cycles in β
           Lyrae-Type Binaries

    • Authors: R. E. Mennickent
      First page: 15
      Abstract: In order to inquire about the nature of the accretion disks formed around the more massive companion in binaries with β Lyrae-type light curves, we review literature presenting some physical and observational properties of these systems. In addition, we inspect the photometric time series of three representative eclipsing systems obtained by the Optical Gravitational Lensing Experiment (OGLE) project during the last decades and compare them with β Lyrae. All these three systems show indications of being semidetached with a more massive B-type component and in a mass transfer stage. They also show long photometric cycles, and two of them show changes in the orbital light curve that can be interpreted in terms of structural changes of the accretion disks, eventually driven by variations in the mass transfer rate.
      Citation: Galaxies
      PubDate: 2022-01-18
      DOI: 10.3390/galaxies10010015
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 16: Translating Neutron Star Observations to
           Nuclear Symmetry Energy via Deep Neural Networks

    • Authors: Plamen G. Krastev
      First page: 16
      Abstract: One of the most significant challenges involved in efforts to understand the equation of state of dense neutron-rich matter is the uncertain density dependence of the nuclear symmetry energy. In particular, the nuclear symmetry energy is still rather poorly constrained, especially at high densities. On the other hand, detailed knowledge of the equation of state is critical for our understanding of many important phenomena in the nuclear terrestrial laboratories and the cosmos. Because of its broad impact, pinning down the density dependence of the nuclear symmetry energy has been a long-standing goal of both nuclear physics and astrophysics. Recent observations of neutron stars, in both electromagnetic and gravitational-wave spectra, have already constrained significantly the nuclear symmetry energy at high densities. The next generation of telescopes and gravitational-wave observatories will provide an unprecedented wealth of detailed observations of neutron stars, which will improve further our knowledge of the density dependence of nuclear symmetry energy, and the underlying equation of state of dense neutron-rich matter. Training deep neural networks to learn a computationally efficient representation of the mapping between astrophysical observables of neutron stars, such as masses, radii, and tidal deformabilities, and the nuclear symmetry energy allows its density dependence to be determined reliably and accurately. In this work, we use a deep learning approach to determine the nuclear symmetry energy as a function of density directly from observational neutron star data. We show, for the first time, that artificial neural networks can precisely reconstruct the nuclear symmetry energy from a set of available neutron star observables, such as masses and radii as measured by, e.g., the NICER mission, or masses and tidal deformabilities as measured by the LIGO/VIRGO/KAGRA gravitational-wave detectors. These results demonstrate the potential of artificial neural networks to reconstruct the symmetry energy and the equation of state directly from neutron star observational data, and emphasize the importance of the deep learning approach in the era of multi-messenger astrophysics.
      Citation: Galaxies
      PubDate: 2022-01-18
      DOI: 10.3390/galaxies10010016
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 17: Fifty Years of Eclipsing Binary Analysis with
           the Wilson–Devinney Model

    • Authors: Josef Kallrath
      First page: 17
      Abstract: The Wilson–Devinney model has—over the last 50 years—become the standard in analyzing eclipsing binary observations. To provide orientation for both active binary and non-binary researchers, it is presented here in historical and on-going as well as astrophysical perspectives. Among the important advances that originated with the model are: the representation of star surfaces as equipotentials for circular and eccentric orbits, leading to four morphological types; simultaneous least-squares light and velocity curve analyses; efficient reflection computation, including multiple reflection; disk theory and disk modeling. Solutions in physical units allowed for the accurate estimation of parameters such as stellar masses and photometric distances; inclusion of types of observables, properly weighted.
      Citation: Galaxies
      PubDate: 2022-01-19
      DOI: 10.3390/galaxies10010017
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 18: Studying Nearby Galactic Planetary Nebulae
           with MUSE: On the Physical Properties of IC 418

    • Authors: Ana Monreal-Ibero , Jeremy R. Walsh
      First page: 18
      Abstract: Spectroscopic mapping of planetary nebulae (PNe) is particularly useful to capture the richness in terms of physical and chemical properties that exist in these objects. The advent of the multi-unit spectroscopic explorer (MUSE), a large integral field unit mounted on the ESO Very Large Telescope, allow us to obtain this information over the whole face of galactic PNe in a reasonable amount of time. This in turn reveals a wealth of information that can bring insight into this structural complexity. Here we discuss new results from commissioning data for the physical properties of IC 418 and succinctly review recently published results on two additional targets (NGC 3132 and NGC 7009). For the newly-analysed PN, electron densities are high with ne([S ii]) displaying a completely different structure than ne([Cl iii]). The electron temperature was relatively uniform, but somewhat higher at the rim as measured by two of the three used diagnostics ([S iii] 6312/9069, and [Ar iii] 5192/7136). The joint results for the three PNe amply illustrate the potential of MUSE for the study of galactic PNe.
      Citation: Galaxies
      PubDate: 2022-01-19
      DOI: 10.3390/galaxies10010018
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 19: A Tail of Two Clumps

    • Authors: Alejandro Cristian Raga, Jorge Cantó, Antonio Castellanos-Ramírez, Jorge Ivan Castorena, Liliana Hernández-Martínez, Ary Rodríguez-González, Pedro Rivera-Ortíz
      First page: 19
      Abstract: We present two axisymmetric simulations of a high velocity clump in a photoionized region: one for the case of a uniform, low density environment and a second one for the case of a clump first traveling within a high density medium and then emerging into a low density environment. We show that the second scenario results in the production of an axial tail of dense material with a linear velocity vs. position ramp (with zero velocity at the high/low density environment transition). This material comes from a confined bow shock (produced by the clump when it was within the dense cloud) that emerges into the low environmental density region.
      Citation: Galaxies
      PubDate: 2022-01-21
      DOI: 10.3390/galaxies10010019
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 20: Seismic and Newtonian Noise in the GW

    • Authors: Lucia Trozzo, Francesca Badaracco
      First page: 20
      Abstract: Gravitational wave detectors aim to measure relative length variations of the order of ΔL/L≃10−21, or less. Thus, any mechanism that is able to reproduce such a tiny variation can, in principle, threaten the sensitivity of these instruments, representing a source of noise. There are many examples of such noise, and seismic and Newtonian noise are among these and will be the subject of this review. Seismic noise is generated by the incessant ground vibration that characterizes Earth. Newtonian noise is instead produced by the tiny fluctuations of the Earth’s gravitational field. These fluctuations are generated by variations of air and soil density near the detector test masses. Soil density variations are produced by the same seismic waves comprising seismic noise. Thus, it makes sense to address these two sources of noise in the same review. An overview of seismic and Newtonian noise is presented, together with a review of the strategies adopted to mitigate them.
      Citation: Galaxies
      PubDate: 2022-01-22
      DOI: 10.3390/galaxies10010020
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 21: TeV Instrumentation: Current and Future

    • Authors: Julian Sitarek
      First page: 21
      Abstract: During the last 20 years, TeV astronomy has turned from a fledgling field, with only a handful of sources, into a fully-developed astronomy discipline, broadening our knowledge on a variety of types of TeV gamma-ray sources. This progress has been mainly achieved due to the currently operating instruments: imaging atmospheric Cherenkov telescopes, surface arrays and water Cherenkov detectors. Moreover, we are at the brink of a next generation of instruments, with a considerable leap in performance parameters. This review summarizes the current status of the TeV astronomy instrumentation, mainly focusing on the comparison of the different types of instruments and analysis challenges, as well as providing an outlook into the future installations. The capabilities and limitations of different techniques of observations of TeV gamma rays are discussed, as well as synergies to other bands and messengers.
      Citation: Galaxies
      PubDate: 2022-01-27
      DOI: 10.3390/galaxies10010021
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 22: Quintessential Inflation: A Tale of Emergent
           and Broken Symmetries

    • Authors: Dario Bettoni, Javier Rubio
      First page: 22
      Abstract: Quintessential inflation provides a unified description of inflation and dark energy in terms of a single scalar degree of freedom, the cosmon. We present here a comprehensive overview of this appealing paradigm, highlighting its key ingredients and keeping a reasonable and homogeneous level of details. After summarizing the cosmological evolution in a simple canonical case, we discuss how quintessential inflation can be embedded in a more general scalar-tensor formulation and its relation to variable gravity scenarios. Particular emphasis is placed on the role played by symmetries. In particular, we discuss the evolution of the cosmon field in terms of ultraviolet and infrared fixed points potentially appearing in quantum gravity formulations and leading to the emergence of scale invariance in the early and late Universe. The second part of the review is devoted to the exploration of the phenomenological consequences of the paradigm. First, we discuss how direct couplings of the cosmon field to matter may affect neutrinos masses and primordial structure formation. Second, we describe how Ricci-mediated couplings to spectator fields can trigger the spontaneous symmetry breaking of internal symmetries such as, but not limited to, global U(1) or Z2 symmetries, and affect a large variety of physical processes in the early Universe.
      Citation: Galaxies
      PubDate: 2022-01-27
      DOI: 10.3390/galaxies10010022
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 23: Acknowledgment to Reviewers of Galaxies in

    • Authors: Galaxies Editorial Office Galaxies Editorial Office
      First page: 23
      Abstract: Rigorous peer-reviews are the basis of high-quality academic publishing [...]
      Citation: Galaxies
      PubDate: 2022-01-29
      DOI: 10.3390/galaxies10010023
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 24: On the Evolution of the Hubble Constant with
           the SNe Ia Pantheon Sample and Baryon Acoustic Oscillations: A Feasibility
           Study for GRB-Cosmology in 2030

    • Authors: Maria Giovanna Dainotti, Biagio De De Simone, Tiziano Schiavone, Giovanni Montani, Enrico Rinaldi, Gaetano Lambiase, Malgorzata Bogdan, Sahil Ugale
      First page: 24
      Abstract: The difference from 4 to 6 σ in the Hubble constant (H0) between the values observed with the local (Cepheids and Supernovae Ia, SNe Ia) and the high-z probes (Cosmic Microwave Background obtained by the Planck data) still challenges the astrophysics and cosmology community. Previous analysis has shown that there is an evolution in the Hubble constant that scales as f(z)=H0/(1+z)η, where H0 is H0(z=0) and η is the evolutionary parameter. Here, we investigate if this evolution still holds by using the SNe Ia gathered in the Pantheon sample and the Baryon Acoustic Oscillations. We assume H0=70kms−1Mpc−1 as the local value and divide the Pantheon into three bins ordered in increasing values of redshift. Similar to our previous analysis but varying two cosmological parameters contemporaneously (H0, Ω0m in the ΛCDM model and H0, wa in the w0waCDM model), for each bin we implement a Markov-Chain Monte Carlo analysis (MCMC) obtaining the value of H0 assuming Gaussian priors to restrict the parameters spaces to values we expect from our prior knowledge of the current cosmological models and to avoid phantom Dark Energy models with w<−1. Subsequently, the values of H0 are fitted with the model f(z). Our results show that a decreasing trend with η∼10−2 is still visible in this sample. The η coefficient reaches zero in 2.0 σ for the ΛCDM model up to 5.8 σ for w0waCDM model. This trend, if not due to statistical fluctuations, could be explained through a hidden astrophysical bias, such as the effect of stretch evolution, or it requires new theoretical models, a possible proposition is the modified gravity theories, f(R). This analysis is meant to further cast light on the evolution of H0 and it does not specifically focus on constraining the other parameters. This work is also a preparatory to understand how the combined probes still show an evolution of the H0 by redshift and what is the current status of simulations on GRB cosmology to obtain the uncertainties on the Ω0m comparable with the ones achieved through SNe Ia.
      Citation: Galaxies
      PubDate: 2022-01-29
      DOI: 10.3390/galaxies10010024
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 25: Optimization of Design Parameters for
           Gravitational Wave Detector DECIGO Including Fundamental Noises

    • Authors: Yuki Kawasaki, Ryuma Shimizu, Tomohiro Ishikawa, Koji Nagano, Shoki Iwaguchi, Izumi Watanabe, Bin Wu, Shuichiro Yokoyama, Seiji Kawamura
      First page: 25
      Abstract: The DECi-hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational wave (GW) detector. DECIGO was originally designed to be sensitive enough to observe primordial GW background (PGW). However, due to the lowered upper limit of the PGW by the Planck observation, further improvement of the target sensitivity of DECIGO is required. In the previous studies, DECIGO’s parameters were optimized to maximize the signal-to-noise ratio (SNR) of the PGW to quantum noise including the effect of diffraction loss. To simulate the SNR more realistically, we optimize DECIGO’s parameters considering the GWs from double white dwarfs (DWDs) and the thermal noise of test masses. We consider two cases of the cutoff frequency of GWs from DWDs. In addition, we consider two kinds of thermal noise: thermal noise in a residual gas and internal thermal noise. To investigate how the mirror geometry affects the sensitivity, we calculate it by changing the mirror mass, keeping the mirror thickness, and vice versa. As a result, we obtained the optimums for the parameters that maximize the SNR that depends on the mirror radius. This result shows that a thick mirror with a large radius gives a good SNR and enables us to optimize the design of DECIGO based on the feasibility study of the mirror size in the future.
      Citation: Galaxies
      PubDate: 2022-02-01
      DOI: 10.3390/galaxies10010025
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 26: Lessons from the Ionised and Molecular Mass
           of Post-CE PNe

    • Authors: Miguel Santander-García, David Jones, Javier Alcolea, Valentín Bujarrabal, Roger Wesson
      First page: 26
      Abstract: Close binary evolution is widely invoked to explain the formation of axisymmetric planetary nebulae after a brief common envelope phase. The evolution of the primary would be interrupted abruptly, its still quite massive envelope being fully ejected to form the PN, which should be more massive than a planetary nebula coming from the same star, were it single. We test this hypothesis by investigating the ionised and molecular masses of a sample consisting of 21 post-common-envelope planetary nebulae, roughly one-fifth of their known total population, and comparing them to a large sample of regular planetary nebulae (not known to host close-binaries). We find that post-common-envelope planetary nebulae arising from single-degenerate systems are, on average, neither more nor less massive than regular planetary nebulae, whereas post-common-envelope planetary nebulae arising from double-degenerate systems are considerably more massive and show substantially larger linear momenta and kinetic energy than the rest. The reconstruction of the common envelope of four objects further suggests that the mass of single-degenerate nebulae actually amounts to a very small fraction of the envelope of their progenitor stars. This leads to the uncomfortable question of where the rest of the envelope is, raising serious doubts on our understanding of these intriguing objects.
      Citation: Galaxies
      PubDate: 2022-02-01
      DOI: 10.3390/galaxies10010026
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 27: SATELLITE: Application to Planetary Nebulae
           IFU Data

    • Authors: Stavros Akras, Hektor Monteiro, Jeremy Walsh, Aleman Isabel, Denise R. Gonçalves, Panayotis Boumis
      First page: 27
      Abstract: The integral field unit (IFU) spectroscopic view of extended ionized nebulae, such as planetary nebulae (PNe), H II regions, and galaxies, has changed the approach of studying these objects, providing a simultaneous characterization in both spatial directions. However, the spatial spaxel-by-spaxel analysis of such nebulae through IFUs is not directly comparable with the results obtained from the traditional slit-aperture spectroscopy or the predictions from 1D modelling. The new Python software called “satellite: Spectroscopic Analysis Tool for intEgraL fieLd unIt daTacubEs” is used in the analysis of the VIMOS and MUSE datacubes of four Galactic PNe. The 2D analysis of line ratio maps has shown important variations from one to another nebular component in NGC 7009 and NGC 6778. In particular, the knots in both PNe are characterized by strong emission from neutral gas that is weak or even absent from the main nebula, indicating significant variation in the ionization state and density structure among the nebular components. The far-UV radiation from the central star results in the photo-evaporation of the dense molecular knots resembling the spectrum of photodissociation regions.
      Citation: Galaxies
      PubDate: 2022-02-01
      DOI: 10.3390/galaxies10010027
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 28: Detecting Gravitational Waves with Advanced

    • Authors: Ilaria Nardecchia
      First page: 28
      Abstract: Advanced Virgo is the European gravitational-wave detector that, along with the American ones, is part of the global network of detectors that have been pinpointing gravitational waves since 2015. These kilometer-scale laser interferometers, measuring the distance between quasi-free-falling mirrors, represent the suitable detectors to explore the Universe through gravitational radiation. The initial Virgo experiment completed several runs of scientific data between 2007 and 2011, establishing the upper limits on the gravitational-wave rate expected for several astrophysical sources. The Advanced Virgo project led this instrument to unprecedented sensitivities making gravitational wave detections a routine occurrence. In this review, the basic techniques to build gravitational-waves interferometers and the upgrades needed to boost their sensitivities, even beyond the classical limit, are presented. The particular case of Advanced Virgo will be described hinting at its future developments, as well.
      Citation: Galaxies
      PubDate: 2022-02-02
      DOI: 10.3390/galaxies10010028
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 29: New Window on the Radio Emission from
           Galaxies, Clusters and Cosmic Web—Conference Summary

    • Authors: Francesca Loi, Tiziana Venturi
      First page: 29
      Abstract: This manuscript summarizes the contributions presented and discussed during the conference “A new window on radio galaxies, clusters and cosmic web: current status and new challenges”. The meeting was held online in March 2021. The works presented during the conference have been published in this associated Special Issue. Here, we outline the scientific context of the published results.
      Citation: Galaxies
      PubDate: 2022-02-07
      DOI: 10.3390/galaxies10010029
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 30: Plasma Diagnostics in the Era of Integral
           Field Spectroscopy

    • Authors: Toshiya Ueta
      First page: 30
      Abstract: To understand the physical conditions of various gaseous systems, plasma diagnostics must be performed properly. To that end, it is equally important to have extinction correction performed properly, even before performing plasma diagnostics. This means that the physical conditions of the target sources—the very quantities to be derived via plasma diagnostics—must be known even before performing extinction correction, because the degree of extinction is determined by comparing the observed spectra of the target sources with their theoretically predicted counterparts. One way to resolve this conundrum is to perform both extinction correction and plasma diagnostics together by iteratively seeking a converged solution. In fact, if these analyses are performed self-consistently, a converged solution can be found based solely on well-calibrated line intensities, given the adopted extinction law and the RV value. However, it is still rare to find these analyses performed numerically rigorously without unnecessary analytical approximations from start to finish. In this contribution for the APN 8e conference, we would like to review this convoluted problem and sort out critical issues based on the results of our recent experiments. It appears that the convoluted theoretical and observational progresses exacerbated by the highly numerical nature of these analyses necessitated a number of analytical simplifications to make the problem analytically tractable in the pre-computer era and that such analytical simplifications still remain rampant in the literature today, even after ample computational resources became readily available. Hence, the community is encouraged to do away with this old habit of sidestepping numerical calculations that was a necessary evil in the past. This is especially true in the context of spatially-resolved 2-D spectroscopy, which obviously conflicts with the uniformity assumption often blindly inherited from 1-D spectroscopy.
      Citation: Galaxies
      PubDate: 2022-02-08
      DOI: 10.3390/galaxies10010030
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 31: Reheating in Runaway Inflation Models via the
           Evaporation of Mini Primordial Black Holes

    • Authors: Ioannis Dalianis, George P. Kodaxis
      First page: 31
      Abstract: We investigate the cosmology of mini Primordial Black Holes (PBHs) produced by large density perturbations that collapse during a stiff fluid domination phase. Such a phase can be realized by a runaway-inflaton model that crosses an inflection point or a sharp feature at the last stage of inflation. Mini PBHs evaporate promptly and reheat the early universe. In addition, we examine two notable implications of this scenario: the possible presence of PBH evaporation remnants in galaxies and a non-zero residual potential energy density for the runaway inflaton that might play the role of the dark energy. We specify the parameter space that this scenario can be realized and we find that a transit PBH domination phase is necessary due to gravitational wave (GW) constraints. A distinct prediction of the scenario is a compound GW signal that might be probed by current and future experiments. We also demonstrate our results employing an explicit inflation model.
      Citation: Galaxies
      PubDate: 2022-02-10
      DOI: 10.3390/galaxies10010031
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 32: A Preliminary Investigation of CSPN in the
           HASH Database

    • Authors: Quentin A. Parker, Zou Xiang, Andreas Ritter
      First page: 32
      Abstract: We present some preliminary findings on the population of planetary nebula where central stars (CSPN) have been independently identified in the HASH catalogue. Many new discoveries and candidates have been found (416 at the time of this writing), adding significantly to the previously known sample of about 600. We also present results from a comparison between our own HASH measurements of CSPN and those provided in existing CSPN catalogues and those from Gaia. We show the value of a federated, multi-wavelength database of Galactic PNe like HASH in terms of not only uncovering faint, new CSPN but of assisting in correct identifications, removing PN mimics with apparent CSPN, correcting incorrect assignments and providing improved positions. HASH provides the community with a comprehensive and reliable resource for any study of the CSPN population of Galactic PNe.
      Citation: Galaxies
      PubDate: 2022-02-11
      DOI: 10.3390/galaxies10010032
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 33: DEATHSTAR—CO Envelope Size and
           Asymmetry of Nearby AGB Stars

    • Authors: Miora Andriantsaralaza, Wouter Vlemmings, Sofia Ramstedt, Elvire De De Beck
      First page: 33
      Abstract: Low- and intermediate-mass stars evolve into asymptotic giant branch (AGB) stars near the end of their lives, losing mass through slow and massive winds. The ejected material creates a chemically-rich expanding envelope around the star, namely the circumstellar envelope (CSE). Investigating the anisotropy of the mass-loss phenomenon on the AGB is crucial in gaining a better understanding of the shaping of the CSE during the transition from AGB star to planetary nebula (PN). We investigate possible signs of deviation from spherical symmetry in the CO-emitting CSEs of 70 AGB stars by analysing their emission maps in CO J=2−1 and 3−2 observed with the Atacama Compact Array, as part of the DEATHSTAR project. We find that about one third of the sources are likely aspherical, as they exhibit large-scale asymmetries that are unlikely to have been created by a smooth wind. Further high-resolution observations would be necessary to investigate the nature of, and the physical processes behind, these asymmetrical structures.
      Citation: Galaxies
      PubDate: 2022-02-12
      DOI: 10.3390/galaxies10010033
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 34: Stochastic Gravitational-Wave Backgrounds:
           Current Detection Efforts and Future Prospects

    • Authors: Arianna I. Renzini, Boris Goncharov, Alexander C. Jenkins, Patrick M. Meyers
      First page: 34
      Abstract: The collection of individually resolvable gravitational wave (GW) events makes up a tiny fraction of all GW signals that reach our detectors, while most lie below the confusion limit and are undetected. Similarly to voices in a crowded room, the collection of unresolved signals gives rise to a background that is well-described via stochastic variables and, hence, referred to as the stochastic GW background (SGWB). In this review, we provide an overview of stochastic GW signals and characterise them based on features of interest such as generation processes and observational properties. We then review the current detection strategies for stochastic backgrounds, offering a ready-to-use manual for stochastic GW searches in real data. In the process, we distinguish between interferometric measurements of GWs, either by ground-based or space-based laser interferometers, and timing-residuals analyses with pulsar timing arrays (PTAs). These detection methods have been applied to real data both by large GW collaborations and smaller research groups, and the most recent and instructive results are reported here. We close this review with an outlook on future observations with third generation detectors, space-based interferometers, and potential noninterferometric detection methods proposed in the literature.
      Citation: Galaxies
      PubDate: 2022-02-14
      DOI: 10.3390/galaxies10010034
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 35: The Blazar Sequence and Its Physical

    • Authors: Elisa Prandini, Gabriele Ghisellini
      First page: 35
      Abstract: Introduced in 1998 to attempt a first unified view of the broad-band emission properties of blazars, the blazar sequence has been extensively used in the past 25 years to guide observations as well as the physical interpretation of the overall emission from these galaxies. In this review, we describe the evolution of the sequence along with the tremendous advances in the observational field, in particular in the gamma-ray band. A new version of the sequence built on TeV-detected objects is also presented. Two extreme classes of objects (MeV and hard-TeV blazars) are included in the discussion, given their relevance for future observatories. Finally, the current physical understanding at the base of the sequence is presented along with the major criticisms to the blazar sequence.
      Citation: Galaxies
      PubDate: 2022-02-15
      DOI: 10.3390/galaxies10010035
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 36: Review of the Advanced LIGO Gravitational
           Wave Observatories Leading to Observing Run Four

    • Authors: Craig Cahillane, Georgia Mansell
      First page: 36
      Abstract: Gravitational waves from binary black hole and neutron star mergers are being regularly detected. As of 2021, 90 confident gravitational wave detections have been made by the LIGO and Virgo detectors. Work is ongoing to further increase the sensitivity of the detectors for the fourth observing run, including installing some of the A+ upgrades designed to lower the fundamental noise that limits the sensitivity to gravitational waves. In this review, we will provide an overview of the LIGO detectors optical configuration and lock acquisition procedure, discuss the detectors’ fundamental and technical noise limits, show the current measured sensitivity, and explore the A+ upgrades currently being installed in the detectors.
      Citation: Galaxies
      PubDate: 2022-02-15
      DOI: 10.3390/galaxies10010036
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 10, Pages 37: Ionization-Gasdynamic Simulations of
           Wind-Blown Nebulae around Massive Stars

    • Authors: Vikram V. Dwarkadas
      First page: 37
      Abstract: Using a code that employs a self-consistent method for computing the effects of photo-ionization on circumstellar gas dynamics, we model the formation of wind-driven nebulae around massive stars. We take into account changes in stellar properties and mass-loss over the star’s evolution. Our simulations show how various properties, such as the density and ionization fraction, change throughout the evolution of the star. The multi-dimensional simulations reveal the presence of strong ionization front instabilities in the main-sequence phase, similar to those seen in galactic ionization fronts. Hydrodynamic instabilities at the interfaces lead to the formation of filaments and clumps that are continually being stripped off and mixed with the low density interior. Even though the winds start out as completely radial, the spherical symmetry is quickly destroyed, and the shocked wind region is manifestly asymmetrical. The simulations demonstrate that it is important to include the effects of the photoionizing photons from the star, and simulations that do not include this may fail to reproduce the observed density profile and ionization structure of wind-blown bubbles around massive stars.
      Citation: Galaxies
      PubDate: 2022-02-17
      DOI: 10.3390/galaxies10010037
      Issue No: Vol. 10, No. 1 (2022)
  • Galaxies, Vol. 9, Pages 93: Bent It Like FRs: Extended Radio AGN in the
           COSMOS Field and Their Large-Scale Environment

    • Authors: Eleni Vardoulaki, Franco Vazza, Eric F. Jiménez-Andrade, Ghassem Gozaliasl, Alexis Finoguenov, Denis Wittor
      First page: 93
      Abstract: A fascinating topic in radio astronomy is how to associate the complexity of observed radio structures with their environment in order to understand their interplay and the reason for the plethora of radio structures found in surveys. In this project, we explore the distortion of the radio structure of Fanaroff–Riley (FR)-type radio sources in the VLA-COSMOS Large Project at 3 GHz and relate it to their large-scale environment. We quantify the distortion by using the angle formed between the jets/lobes of two-sided FRs, namely bent angle (BA). Our sample includes 108 objects in the redshift range 0.08<z<3, which we cross-correlate to a wide range of large-scale environments (X-ray galaxy groups, density fields, and cosmic web probes) in the COSMOS field. The median BA of FRs in COSMOS at zmed∼0.9 is 167.5−37.5+11.5 degrees. We do not find significant correlations between BA and large-scale environments within COSMOS covering scales from a few kpc to several hundred Mpc, nor between BA and host properties. Finally, we compare our observational data to magnetohydrodynamical (MHD) adaptive-mesh simulations ENZO-MHD of two FR sources at z = 0.5 and at z = 1. Although the scatter in BA of the observed data is large, we see an agreement between observations and simulations in the bent angles of FRs, following a mild redshift evolution with BA. We conclude that, for a given object, the dominant mechanism affecting the radio structures of FRs could be the evolution of the ambient medium, where higher densities of the intergalactic medium at lower redshifts as probed by our study allow more space for jet interactions.
      Citation: Galaxies
      PubDate: 2021-11-05
      DOI: 10.3390/galaxies9040093
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 94: A Brown Dwarf Companion to the Nova-like
           Variable RW Tri

    • Authors: Zhibin Dai, Shengbang Qian, Indika Medagangoda
      First page: 94
      Abstract: The orbital period of Nova-like variable RW Tri is expected to experience a long-term evolution due to a stable mass transfer from the red dwarf to the white dwarf. By adding 297 new eclipse timings obtained from our own observations and a cross-identification of many databases, we fully reinvestigated the variations in orbital period of RW Tri, based on a total of 658 data points spanning over 80 years. The new O-C diagram demonstrates a more complicate pattern than a pure sinusoidal modulation shown in the previous O-C analyses. The best fit of the O-C variations is a quadratic-plus-sinusoidal curve with a period of 22.66 (2) years and a typical decrease rate of P˙ = −2d.32(4) × 10−9 yr−1. To explain secular orbital period decrease, the magnetic braking effect is required to cause the orbital angular moment loss in RW Tri with a mass ratio less than unity, while a conserved mass transfer is also enough for RW Tri with a mass ratio larger than unity. No matter what the mass ratio is, a slightly enhanced mass transfer rate, 2.4–5.3 × 10−9 M⊙ yr−1, derived from our O-C diagram, providing an evidence supporting the disk instability model and the standard/revised models of cataclysmic variable evolution, is almost the same as that obtained from the light-curve modeling. This further confirms our observed orbital period decrease and the controversial system parameter, mass transfer rate. Our updated O-C analysis further verifies the claimed cyclical changes of orbital period with a period range of 21–24 years, which is approximately one half of the results in the literature. In accordance with the light-travel time effect, this periodical variation shown in our new O-C diagram indicates a brown dwarf hidden in RW Tri at a coplanar orbit. Note that the large scatter in the data range of 0–3 × 104 cycles requires the high-precision photometry in the longer base line in the future.
      Citation: Galaxies
      PubDate: 2021-11-05
      DOI: 10.3390/galaxies9040094
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 95: Accounting for Selection Bias and Redshift
           Evolution in GRB Radio Afterglow Data

    • Authors: Maria Dainotti, Delina Levine, Nissim Fraija, Poonam Chandra
      First page: 95
      Abstract: Gamma-ray Bursts (GRBs) are highly energetic events that can be observed at extremely high redshift. However, inherent bias in GRB data due to selection effects and redshift evolution can significantly skew any subsequent analysis. We correct for important variables related to the GRB emission, such as the burst duration, T90*, the prompt isotropic energy, Eiso, the rest-frame end time of the plateau emission, Ta,radio*, and its correspondent luminosity La,radio, for radio afterglow. In particular, we use the Efron–Petrosian method presented in 1992 for the correction of our variables of interest. Specifically, we correct Eiso and T90* for 80 GRBs, and La,radio and Ta,radio* for a subsample of 18 GRBs that present a plateau-like flattening in their light curve. Upon application of this method, we find strong evolution with redshift in most variables, particularly in La,radio, with values similar to those found in past and current literature in radio, X-ray and optical wavelengths, indicating that these variables are susceptible to observational bias. This analysis emphasizes the necessity of correcting observational data for evolutionary effects to obtain the intrinsic behavior of correlations to use them as discriminators among the most plausible theoretical models and as reliable cosmological tools.
      Citation: Galaxies
      PubDate: 2021-11-07
      DOI: 10.3390/galaxies9040095
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 96: Bound on Photon Circular Orbits in General
           Relativity and Beyond

    • Authors: Sumanta Chakraborty
      First page: 96
      Abstract: The existence of a photon circular orbit can tell us a lot about the nature of the underlying spacetime, since it plays a pivotal role in the understanding of the characteristic signatures of compact objects, namely the quasi-normal modes and shadow radius. For this purpose, determination of the location of the photon circular orbit is of utmost importance. In this work, we derive bounds on the location of the photon circular orbit around compact objects within the purview of general relativity and beyond. As we have explicitly demonstrated, contrary to the earlier results in the context of general relativity, the bound on the location of the photon circular orbit is not necessarily an upper bound. Depending on the matter content, it is possible to arrive at a lower bound as well. This has interesting implications for the quasi-normal modes and shadow radius, the two key observables related to the strong field tests of gravity. Besides discussing the bound for higher dimensional general relativity, we have also considered how the bound on the photon circular orbits gets modified in the braneworld scenario, for pure Lovelock and general Lovelock theories of gravity. Implications of these results for compact objects were also discussed.
      Citation: Galaxies
      PubDate: 2021-11-07
      DOI: 10.3390/galaxies9040096
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 97: A Multiwavelength Dynamical State Analysis of
           ACT-CL J0019.6+0336

    • Authors: Denisha S. Pillay, David J. Turner, Matt Hilton, Kenda Knowles, Kabelo C. Kesebonye, Kavilan Moodley, Tony Mroczkowski, Nadeem Oozeer, Christoph Pfrommer, Sinenhlanhla P. Sikhosana, Edward J. Wollack
      First page: 97
      Abstract: In our study, we show a multiwavelength view of ACT-CL J0019.6+0336 (which hosts a radio halo), to investigate the cluster dynamics, morphology, and ICM. We use a combination of XMM-Newton images, Dark Energy Survey (DES) imaging and photometry, SDSS spectroscopic information, and 1.16 GHz MeerKAT data to study the cluster properties. Various X-ray and optical morphology parameters are calculated to investigate the level of disturbance. We find disturbances in two X-ray parameters and the optical density map shows elongated and axisymmetric structures with the main cluster component southeast of the cluster centre and another component northwest of the cluster centre. We also find a BCG offset of ∼950 km/s from the mean velocity of the cluster, and a discrepancy between the SZ mass, X-ray mass, and dynamical mass (MX,500 and MSZ,500 lies >3σ away from Mdyn,500), showing that J0019 is a merging cluster and probably in a post-merging phase.
      Citation: Galaxies
      PubDate: 2021-11-08
      DOI: 10.3390/galaxies9040097
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 98: Probing Gamma-Ray Burst VHE Emission with the
           Southern Wide-Field-of-View Gamma-Ray Observatory

    • Authors: Giovanni La Mura, Ulisses Barres de Almeida, Ruben Conceição, Alessandro De Angelis, Francesco Longo, Mário Pimenta, Bernardo Tomé, Davide Miceli
      First page: 98
      Abstract: Recent observations have confirmed that Gamma-Ray Burst (GRB) afterglows produce Very High-Energy radiation (VHE, E>100GeV). This highly anticipated discovery opens new scenarios in the interpretation of GRBs and in their role as probes of Extragalactic Background Light (EBL) and Lorentz Invariance Violation (LIV). However, some fundamental questions about the actual nature of VHE emission in GRBs and its evolution during the burst are still unsolved. These questions will be difficult to address, even with future imaging Cherenkov telescopes, such as the Cherenkov Telescope Array (CTA). Here we investigate the prospects of gamma-ray sky monitoring with Extensive Air Showers arrays (EAS) to address these problems. We discuss the theoretical aspects connected with VHE radiation emission and the implications that its temporal evolution properties have on the interpretation of GRBs. By revisiting the high-energy properties of some Fermi-LAT detected GRBs, we estimate the typical fluxes expected in the VHE band and compare them with a range of foreseeable instrument performances, based on the Southern Wide Field-of-view Gamma-ray Observatory concept (SWGO). We focus our analysis on how different instrument capabilities affect the chances to explore the burst onset and early evolution in VHE, providing invaluable complementary information with respect to Cherenkov telescope observations. We show that under the assumption of conditions already observed in historical events, the next-generation ground monitoring detectors can actually contribute to answer several key questions.
      Citation: Galaxies
      PubDate: 2021-11-08
      DOI: 10.3390/galaxies9040098
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 99: Discovery of 178 Giant Radio Galaxies in 1059
           deg2 of the Rapid ASKAP Continuum Survey at 888 MHz

    • Authors: Heinz Andernach, Eric F. Jiménez-Andrade, Anthony G. Willis
      First page: 99
      Abstract: We report the results of a visual inspection of images of the Rapid ASKAP Continuum Survey (RACS) in search of extended radio galaxies (ERG) that reach or exceed linear sizes on the order of one Megaparsec. We searched a contiguous area of 1059 deg2 from RAJ = 20h20m to 06h20m, and −50∘<DecJ<−40∘, which is covered by deep multi-band optical images of the Dark Energy Survey (DES) and in which previously only three ERGs larger than 1 Mpc had been reported. For over 1800 radio galaxy candidates inspected, our search in optical and infrared images resulted in hosts for 1440 ERG, for which spectroscopic and photometric redshifts from various references were used to convert their largest angular size (LAS) to projected linear size (LLS). This resulted in 178 newly discovered giant radio sources (GRS) with LLS >1 Mpc, of which 18 exceed 2 Mpc and the largest one is 3.4 Mpc. Their redshifts range from 0.02 to ∼2.0, but only 10 of the 178 new GRS have spectroscopic redshifts. For the 146 host galaxies, the median r-band magnitude and redshift are 20.9 and 0.64, while for the 32 quasars or candidates these are 19.7 and 0.75. Merging the six most recent large compilations of GRS results in 458 GRS larger than 1 Mpc, so we were able to increase this number by ∼39% to 636.
      Citation: Galaxies
      PubDate: 2021-11-09
      DOI: 10.3390/galaxies9040099
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 100: Are Disks of Satellites Comprised of Tidal
           Dwarf Galaxies'

    • Authors: Michal Bílek, Ingo Thies, Pavel Kroupa, Benoit Famaey
      First page: 100
      Abstract: It was found that satellites of nearby galaxies can form flattened co-rotating structures called disks of satellites or planes of satellites. Their existence is not expected by the current galaxy formation simulations in the standard dark matter-based cosmology. On the contrary, modified gravity offers a promising alternative: the objects in the disks of satellites are tidal dwarf galaxies, that is, small galaxies that form from tidal tails of interacting galaxies. After introducing the topic, we review here our work on simulating the formation of the disks of satellites of the Milky Way and Andromeda galaxies. The initial conditions of the simulation were tuned to reproduce the observed positions, velocities and disk orientations of the galaxies. The simulation showed that the galaxies had a close flyby 6.8 Gyr ago. One of the tidal tails produced by the Milky Way was captured by Andromeda. It formed a cloud of particles resembling the disk of satellites at Andromeda by its size, orientation, rotation and mass. A hint of a disk of satellites was formed at the Milky Way too. In addition, the encounter induced a warp in the disk of the simulated Milky Way that resembles the real warp by its magnitude and orientation. We present here, for the first time, the proper motions of the members of the disk of satellites of Andromeda predicted by our simulation. Finally, we point out some of the remaining open questions which this hypothesis, for the formation of disks of satellites, brings up.
      Citation: Galaxies
      PubDate: 2021-11-10
      DOI: 10.3390/galaxies9040100
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 101: Detectability of Continuous Gravitational
           Waves from Magnetically Deformed Neutron Stars

    • Authors: Jacopo Soldateschi, Niccolò Bucciantini
      First page: 101
      Abstract: Neutron stars are known to contain extremely powerful magnetic fields. Their effect is to deform the shape of the star, leading to the potential emission of continuous gravitational waves. The magnetic deformation of neutron stars, however, depends on the geometry and strength of their internal magnetic field as well as on their composition, described by the equation of state. Unfortunately, both the configuration of the magnetic field and the equation of state of neutron stars are unknown, and assessing the detectability of continuous gravitational waves from neutron stars suffers from these uncertainties. Using our recent results relating the magnetic deformation of a neutron star to its mass and radius—based on models with realistic equations of state currently allowed by observational and nuclear physics constraints—and considering the Galactic pulsar population, we assess the detectability of continuous gravitational waves from pulsars in the galaxy by current and future gravitational waves detectors.
      Citation: Galaxies
      PubDate: 2021-11-10
      DOI: 10.3390/galaxies9040101
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 102: Discovery of Rare Dying Radio Galaxies Using

    • Authors: Nadeem Oozeer, Lawrence Rudnick, Michael F. Bietenholz, Tiziana Venturi, Kenda Knowles, Konstantinos Kolokythas, Nceba Mhlahlo
      First page: 102
      Abstract: Dying radio galaxies represent a stage of the evolution of active galactic nuclei (AGN), during which the accreting central black hole has switched off and/or falls to such a low level that the plasma outflow can no longer be sustained. When this happens, the radio source undergoes a period of fading, the dying phase, before it disappears completely. We present the study of three potential dying radio sources using the MeerKAT radio telescope: MKT J072851.2-752743, MKT J001940.4-654722, and ACO 548B. The identification as dying radio sources came from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). We carry out a multi-wavelength analysis of the sources and derive their energetics. The ages of the sources are ∼30–70 Myr, they have magnetic fields of the order of a few μG, and they have relatively low radio power. Their potential optical counterparts are associated with massive galaxies. We show that ACO 548B, previously classified as two peripheral relic radio sources, is a dying radio galaxy. With its good sensitivity and resolution, MeerKAT is an ideal instrument to detect potential dying radio sources, and contribute to the understanding of the evolution of AGN population.
      Citation: Galaxies
      PubDate: 2021-11-10
      DOI: 10.3390/galaxies9040102
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 103: Quantum Gravity Phenomenology Induced in the
           Propagation of UHECR, a Kinematical Solution in Finsler and Generalized
           Finsler Spacetime

    • Authors: Marco Danilo Claudio Torri
      First page: 103
      Abstract: It is well-known that the universe is opaque to the propagation of Ultra-High-Energy Cosmic Rays (UHECRs) since these particles dissipate energy during their propagation interacting with the background fields present in the universe, mainly with the Cosmic Microwave Background (CMB) in the so-called GZK cut-off phenomenon. Some experimental evidence seems to hint at the possibility of a dilation of the GZK predicted opacity sphere. It is well-known that kinematical perturbations caused by supposed quantum gravity (QG) effects can modify the foreseen GZK opacity horizon. The introduction of Lorentz Invariance Violation can indeed reduce, and in some cases making negligible, the CMB-UHECRs interaction probability. In this work, we explore the effects induced by modified kinematics in the UHECR lightest component phenomenology from the QG perspective. We explore the possibility of a geometrical description of the massive fermions interaction with the supposed quantum structure of spacetime in order to introduce a Lorentz covariance modification. The kinematics are amended, modifying the dispersion relations of free particles in the context of a covariance-preserving framework. This spacetime description requires a more general geometry than the usual Riemannian one, indicating, for instance, the Finsler construction and the related generalized Finsler spacetime as ideal candidates. Finally we investigate the correlation between the magnitude of Lorentz covariance modification and the attenuation length of the photopion production process related to the GZK cut-off, demonstrating that the predicted opacity horizon can be dilated even in the context of a theory that does not require any privileged reference frame.
      Citation: Galaxies
      PubDate: 2021-11-14
      DOI: 10.3390/galaxies9040103
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 104: Electromagnetic Precursors of Short Gamma-Ray
           Bursts as Counterparts of Gravitational Waves

    • Authors: Jie-Shuang Wang, Liang-Duan Liu
      First page: 104
      Abstract: Precursor emissions are found in some short gamma-ray bursts (SGRBs). In this paper, we review the theories and observations of the SGRB precursor and discuss its prospect as an electromagnetic counterpart of the gravitational wave event produced by neutron star (NS) mergers. The observed luminosity, spectrum, and duration of precursors are explained by the magnetospheric interaction model during the inspiral or the cocoon/jet shock breakout model during the jet propagation. In general, these two models predict that the precursor will be weaker than the main GRB, but will be of a larger opening angle, which makes it an advantageous gamma-ray counterpart for NS mergers in the local Universe, especially for NS - black hole mergers with very low mass ratios, in which the main GRBs are not expected. The joint observation of the precursor, SGRB, and gravitational wave will help to reveal the jet launch mechanism and post-merger remnant.
      Citation: Galaxies
      PubDate: 2021-11-15
      DOI: 10.3390/galaxies9040104
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 105: Pilot Study and Early Results of the Cosmic
           Filaments and Magnetism Survey with Nenufar: The Coma Cluster Field

    • Authors: Etienne Bonnassieux, Evangelia Tremou, Julien N. Girard, Alan Loh, Valentina Vacca, Stéphane Corbel, Baptiste Cecconi, Jean-Mathias Grießmeier, Léon V. E. Koopmans, Michel Tagger, Gilles Theureau, Philippe Zarka
      First page: 105
      Abstract: NenuFAR, the New Extension in Nancay Upgrading LOFAR, is currently in its early science phase. It is in this context that the Cosmic Filaments and Magnetism Pilot Survey is observing sources with the array as it is still under construction—with 57 (56 core, 1 distant) out of a total planned 102 (96 core, 6 distant) mini-arrays online at the time of observation—to get a first look at the low-frequency sky with NenuFAR. One of its targets is the Coma galaxy cluster: a well-known object, host of the prototype radio halo. It also hosts other features of scientific import, including a radio relic, along with a bridge of emission connecting it with the halo. It is thus a well-studied object.In this paper, we show the first confirmed NenuFAR detection of the radio halo and radio relic of the Coma cluster at 34.4 MHz, with associated intrinsic flux density estimates: we find an integrated flux value of 106.3 ± 3.5 Jy for the radio halo, and 102.0 ± 7.4 Jy for the radio relic. These are upper bound values, as they do not include point-source subtraction. We also give an explanation of the technical difficulties encountered in reducing the data, along with steps taken to resolve them. This will be helpful for other scientific projects which will aim to make use of standalone NenuFAR imaging observations in the future.
      Citation: Galaxies
      PubDate: 2021-11-16
      DOI: 10.3390/galaxies9040105
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 106: The eMERLIN and EVN View of FR 0 Radio

    • Authors: Ranieri D. Baldi, Gabriele Giovannini, Alessandro Capetti
      First page: 106
      Abstract: We present the results from high-resolution observations carried out with the eMERLIN UK-array and the European VLBI network (EVN) for a sample of 15 FR 0s, i.e., compact core-dominated radio sources associated with nearby early-type galaxies (ETGs), which represent the bulk of the local radio galaxy population. The 5 GHz eMERLIN observations available for five objects exhibit sub-mJy core components and reveal pc-scale twin jets for four out of five FR 0s once the eMERLIN and JVLA archival visibilities data are combined. The 1.66 GHz EVN observations available for 10 FR 0s display one- and two-sided jetted morphologies and compact cores. The pc-scale core emission contributes, on average, to about one tenth of the total extended radio emission, although we noted an increasing core contribution for flat-/inverted-spectrum sources. We found an unprecedented linear correlation between the pc-scale core luminosity (∼1021.3–1023.6 W Hz−1) and [O III] line luminosity, generally considered as proxy of the accretion power, for a large sample of LINER-type radio-loud low-luminosity active nuclei, all hosted in massive ETGs, which include FR 0s and FR Is. This result represents further evidence of a common jet–disc coupling in FR 0s and FR Is, despite then differing in kpc-scale radio structure. For our objects and for other FR 0 samples reported in the literature, we estimated the jet brightness sidedness ratios, which typically range between one and three. This parameter roughly gauges the jet bulk Lorentz factor Γ, which turns out to range from 1 to 2.5 for most of the sample. This corroborates the scenario that FR 0s are characterized by mildly relativistic jets, possibly as a result of lower-spinning black holes (BHs) than the highly spinning BHs of relativistic-jetted radio galaxies, FR Is.
      Citation: Galaxies
      PubDate: 2021-11-18
      DOI: 10.3390/galaxies9040106
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 107: How Are Red and Blue Quasars Different'
           The Radio Properties

    • Authors: Victoria A. Fawcett, David M. Alexander, David J. Rosario, Lizelke Klindt
      First page: 107
      Abstract: A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the majority of cases) that the accretion disc is obscured by a column of dust which extinguishes the shorter-wavelength blue emission. In this paper, we summarize recent work by our group, where we find fundamental differences in the radio properties of SDSS optically-selected red quasars. We also present new analyses, using a consistent color-selected quasar parent sample matched to four radio surveys (FIRST, VLA Stripe 82, VLA COSMOS 3 GHz, and LoTSS DR1) across a frequency range 144 MHz–3 GHz and four orders of magnitude in radio flux. We show that red quasars have enhanced small-scale radio emission (∼kpc) that peaks around the radio-quiet threshold (defined as the ratio of 1.4 GHz luminosity to 6 μm luminosity) across the four radio samples. Exploring the potential mechanisms behind this enhancement, we rule out star-formation and propose either small-scale synchrotron jets, frustrated jets, or dusty winds interacting with the interstellar medium; the latter two scenarios would provide a more direct connection between opacity (dust; gas) and the production of the radio emission. In our future study, using new multi-band uGMRT data, we aim to robustly distinguish between these scenarios.
      Citation: Galaxies
      PubDate: 2021-11-19
      DOI: 10.3390/galaxies9040107
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 108: Radio and X-ray Observations of the Restarted
           Radio Galaxy in the Galaxy Cluster CL 0838+1948

    • Authors: Simona Giacintucci, Tracy Clarke, Namir E. Kassim, Wendy Peters, Emil Polisensky
      First page: 108
      Abstract: We present VLA Low-band Ionosphere and Transient Experiment (VLITE) 338 MHz observations of the galaxy cluster CL 0838+1948. We combine the VLITE data with Giant Metrewave Radio Telescope 610 MHz observations and survey data. The central galaxy hosts a 250 kpc source whose emission is dominated by two large lobes at low frequencies. At higher frequencies, a pair of smaller lobes (∼30 kpc) is detected within the galaxy optical envelope. The observed morphology is consistent with a restarted radio galaxy. The outer lobes have a spectral index αout=1.6, indicating that they are old, whereas the inner lobes have αinn=0.6, typical for an active source. Spectral modeling confirms that the outer emission is a dying source whose nuclear activity switched off not more than 110 Myr ago. Using archival Chandra X-ray data, we compare the radio and hot gas emission. We find that the active radio source is contained within the innermost and X-ray brightest region, possibly a galactic corona. Alternatively, it could be the remnant of a larger cool core whose outer layers have been heated by the former epoch of activity that has generated the outer lobes.
      Citation: Galaxies
      PubDate: 2021-11-21
      DOI: 10.3390/galaxies9040108
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 109: Magnetogenesis and the Cosmic Web: A Joint
           Challenge for Radio Observations and Numerical Simulations

    • Authors: Franco Vazza, Nicola Locatelli, Kamlesh Rajpurohit, Serena Banfi, Paola Domínguez-Fernández, Denis Wittor, Matteo Angelinelli, Giannandrea Inchingolo, Marisa Brienza, Stefan Hackstein, Daniele Dallacasa, Claudio Gheller, Marcus Brüggen, Gianfranco Brunetti, Annalisa Bonafede, Stefano Ettori, Chiara Stuardi, Daniela Paoletti, Fabio Finelli
      First page: 109
      Abstract: The detection of the radio signal from filaments in the cosmic web is crucial to distinguish possible magnetogenesis scenarios. We review the status of the different attempts to detect the cosmic web at radio wavelengths. This is put into the context of the advanced simulations of cosmic magnetism carried out in the last few years by our MAGCOW project. While first attempts of imaging the cosmic web with the MWA and LOFAR have been encouraging and could discard some magnetogenesis models, the complexity behind such observations makes a definitive answer still uncertain. A combination of total intensity and polarimetric data at low radio frequencies that the SKA and LOFAR2.0 will achieve is key to removing the existing uncertainties related to the contribution of many possible sources of signal along deep lines of sight. This will make it possible to isolate the contribution from filaments, and expose its deep physical connection with the origin of extragalactic magnetism.
      Citation: Galaxies
      PubDate: 2021-11-23
      DOI: 10.3390/galaxies9040109
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 110: Hot Spots Drift in Synchronous and
           Asynchronous Polars: Results of Three-Dimensional Numerical Simulation

    • Authors: Dmitry Bisikalo, Andrey Sobolev, Andrey Zhilkin
      First page: 110
      Abstract: In this paper, the characteristics of hot spots on an accretor surface are investigated for two types of polars: the eclipsing synchronous polar V808 Aur and the non-eclipsing asynchronous polar CD Ind in configuration of an offset and non-offset magnetic dipole. The drift of hot spots is analyzed based on the results of numerical calculations and maps of the temperature distribution over the accretor surface. It is shown that a noticeable displacement of the spots is determined by the ratio of ballistic and magnetic parts of the jet trajectory. In the synchronous polar, the dominant influence on the drift of hot spots is exerted by variations in the mass transfer rate, which entail a change in the ballistic part of the trajectory. It was found that when the mass transfer rate changes within the range of 10−10M⊙/year to 10−7M⊙/year, the displacement of the hot spot in latitude and longitude can reach 30∘. In the asynchronous polar, a change in the position of hot spots is mainly defined by the properties of the white dwarf magnetosphere, and the displacement of hot spots in latitude and longitude can reach 20∘.
      Citation: Galaxies
      PubDate: 2021-11-28
      DOI: 10.3390/galaxies9040110
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 111: Modelling the Energy Spectra of Radio Relics

    • Authors: Denis Wittor, Matthias Hoeft, Marcus Brüggen
      First page: 111
      Abstract: Radio relics are diffuse synchrotron sources that illuminate shock waves in the intracluster medium. In recent years, radio telescopes have provided detailed observations about relics. Consequently, cosmological simulations of radio relics need to provide a similar amount of detail. In this methodological work, we include information on adiabatic compression and expansion, which have been neglected in the past in the modelling of relics. In a cosmological simulation of a merging galaxy cluster, we follow the energy spectra of shock accelerated cosmic-ray electrons using Lagrangian tracer particles. On board of each tracer particle, we compute the temporal evolution of the energy spectrum under the influence of synchrotron radiation, inverse Compton scattering, and adiabatic compression and expansion. Exploratory tests show that the total radio power and, hence, the integrated radio spectrum are not sensitive to the adiabatic processes. This is attributed to small changes in the compression ratio over time.
      Citation: Galaxies
      PubDate: 2021-12-01
      DOI: 10.3390/galaxies9040111
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 112: Spectral Index of the Filaments in the Abell
           523 Radio Halo

    • Authors: Valentina Vacca, Federica Govoni, Richard A. Perley, Matteo Murgia, Ettore Carretti, Francesca Loi, Luigina Feretti, Gabriele Giovannini
      First page: 112
      Abstract: The galaxy cluster Abell 523 hosts a radio halo characterized by the presence of two filaments transversely located with respect to the cluster merger axis. In this paper, we present a spectral index image of these filaments between 1.410 and 1.782 GHz obtained with Jansky Very Large Array observations. We find a steepening of the spectral index of the filaments at frequencies ≳1.4 GHz and an indication that bright patches are characterized by flat spectral indices. Our results are consistent with a scenario of highly-efficient turbulence induced by merger phenomena.
      Citation: Galaxies
      PubDate: 2021-12-04
      DOI: 10.3390/galaxies9040112
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 113: The SVOM Mission

    • Authors: Maria Grazia Bernardini, Bertrand Cordier, Jianyan Wei
      First page: 113
      Abstract: SVOM (Space-based multiband astronomical Variable Objects Monitor) is a sino-french mission that is dedicated to Gamma-Ray Burst (GRB) science, expected to be launched in mid 2023. The mission includes four space-based and three ground-based instruments that, working together, will discover GRBs and provide rapid multi-wavelength follow-up in order to obtain a complete coverage of the GRB emission over seven decades in energy, from the trigger up to the very late phases of the afterglow. Thanks to its characteristics, SVOM will play a crucial role in time-domain and multi-messenger astronomy.
      Citation: Galaxies
      PubDate: 2021-12-04
      DOI: 10.3390/galaxies9040113
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 114: The Nature of Micro-Variability in Blazars

    • Authors: James R. Webb, Viviana Arroyave, Douglas Laurence, Stephen Revesz, Gopal Bhatta, Hal Hollingsworth, Sarah Dhalla, Emily Howard, Michael Cioffi
      First page: 114
      Abstract: We present the results of a long-term study designed to investigate the nature of micro-variability in blazars carried out primarily at the Southeastern Association for Research in Astronomy (SARA) observatories. We analyzed micro-variability data of fifteen OVV quasars and BL Lac sources collected from 1995 to 2021. The data set consists of single-band light curves interspersed with multi-color and micro-variability observations. This paper reports over 900 nights of CCD observations. We also incorporated observations from other observers as well as observations gleaned from the literature into our analysis. We employed differential photometry to measure magnitudes and then construct the long-term and micro-variability light curves. Our results indicate that there is no correlation between the presence of micro-variations and the brightness of the source. We present a viable theory to explain the intermittent micro-variability as pulses of radiation emitted by individual turbulent cells in the relativistic jet, which are stimulated by a passing shock wave. We present model fits and test results for various data sets, including WEBT light curves, Kepler light curves and a TESS light curve. Although the consensus in the community is that blazar jets must be turbulent, the identification of micro-variations as manifestations of actual turbulent cells is important for modeling these turbulent jets. We can obtain estimates of cell sizes (assuming a shock speed), and the distribution of cell sizes derived from observations is consistent with numerical simulation predictions.
      Citation: Galaxies
      PubDate: 2021-12-04
      DOI: 10.3390/galaxies9040114
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 115: Multi-Wavelength Study of a Proto-BCG at z =

    • Authors: Quirino D’Amato, Isabella Prandoni, Marisa Brienza, Roberto Gilli, Cristian Vignali, Rosita Paladino, Francesca Loi, Marcella Massardi, Marco Mignoli, Stefano Marchesi, Alessandro Peca, Preshanth Jagannathan
      First page: 115
      Abstract: In this work we performed a spectral energy distribution (SED) analysis in the optical/infrared band of the host galaxy of a proto-brightest bluster galaxy (BCG, NVSS J103023 + 052426) in a proto-cluster at z = 1.7. We found that it features a vigorous star formation rate (SFR) of ∼570 M⊙/yr and a stellar mass of M*∼3.7×1011M⊙; the high corresponding specific SFR = 1.5±0.5Gyr−1 classifies this object as a starburst galaxy that will deplete its molecular gas reservoir in ∼3.5×108 yr. Thus, this system represents a rare example of a proto-BCG caught during the short phase of its major stellar mass assembly. Moreover, we investigated the nature of the host galaxy emission at 3.3 mm. We found that it originates from the cold dust in the interstellar medium, even though a minor non-thermal AGN contribution cannot be completely ruled out. Finally, we studied the polarized emission of the lobes at 1.4 GHz. We unveiled a patchy structure where the polarization fraction increases in the regions in which the total intensity shows a bending morphology; in addition, the magnetic field orientation follows the direction of the bendings. We interpret these features as possible indications of an interaction with the intracluster medium. This strengthens the hypothesis of positive AGN feedback, as inferred in previous studies of this object on the basis of X-ray/mm/radio analysis. In this scenario, the proto-BCG heats the surrounding medium and possibly enhances the SFR in nearby galaxies.
      Citation: Galaxies
      PubDate: 2021-12-07
      DOI: 10.3390/galaxies9040115
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 116: Role of Magnetic Fields in Ram Pressure
           Stripped Galaxies

    • Authors: Ancla Müller, Alessandro Ignesti, Bianca Poggianti, Alessia Moretti, Mpati Ramatsoku, Ralf-Jürgen Dettmar
      First page: 116
      Abstract: Ram-pressure stripping is a crucial evolutionary driver for cluster galaxies and jellyfish galaxies characterized by very extended tails of stripped gas, and they are the most striking examples of it in action. Recently, those extended tails are found to show ongoing star formation, raising the question of how the stripped, cold gas can survive long enough to form new stars outside the stellar disk. In this study, we summarize the most recent results achieved within the GASP collaboration to provide a holistic explanation for this phenomenon. We focus on two textbook examples of jellyfish galaxies, JO206 and JW100, for which, via multi-wavelength observations from radio to X-ray and numerical simulations, we have explored the different gas phases (neutral, molecular, diffuse-ionized, and hot). Based on additional multi-phase gas studies, we now propose a scenario of stripped tail evolution including all phases that are driven by a magnetic draping sheath, where the intracluster turbulent magnetized plasma condenses onto the galaxy disk and tail and produces a magnetized interface that protects the stripped galaxy tail gas from evaporation. In such a scenario, the accreted environmental plasma can cool down and eventually join the tail gas, hence providing additional gas to form stars. The implications of our findings can shed light on the more general scenario of draping, condensation, and cooling of hot gas surrounding cold clouds that is fundamental in many astrophysical phenomena.
      Citation: Galaxies
      PubDate: 2021-12-11
      DOI: 10.3390/galaxies9040116
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 117: A GMRT Narrowband vs. Wideband Analysis of
           the ACT-CL J0034.40225 Field Selected from the ACTPol Cluster Sample+

    • Authors: Sinenhlanhla P. Sikhosana, Kenda Knowles, C. H. Ishwara-Chandra, Matt Hilton, Kavilan Moodley, Neeraj Gupta
      First page: 117
      Abstract: Low frequency radio observations of galaxy clusters are a useful probe of the non-thermal intracluster medium (ICM), through observations of diffuse radio emission such as radio halos and relics. Current formation theories cannot fully account for some of the observed properties of this emission. In this study, we focus on the development of interferometric techniques for extracting extended, faint diffuse emissions in the presence of bright, compact sources in wide-field and broadband continuum imaging data. We aim to apply these techniques to the study of radio halos, relics and radio mini-halos using a uniformly selected and complete sample of galaxy clusters selected via the Sunyaev-Zel’dovich (SZ) effect by the Atacama Cosmology Telescope (ACT) project, and its polarimetric extension (ACTPol). We use the upgraded Giant Metrewave Radio Telescope (uGMRT) for targeted radio observations of a sample of 40 clusters. We present an overview of our sample, confirm the detection of a radio halo in ACT−CL J0034.4+0225, and compare the narrowband and wideband analysis results for this cluster. Due to the complexity of the ACT−CL J0034.4+0225 field, we use three pipelines to process the wideband data. We conclude that the experimental spam wideband pipeline produces the best results for this particular field. However, due to the severe artefacts in the field, further analysis is required to improve the image quality.
      Citation: Galaxies
      PubDate: 2021-12-12
      DOI: 10.3390/galaxies9040117
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 118: γ-Ray Flux and Spectral Variability of
           Blazar Ton 599 during Its 2021 Flare

    • Authors: Bhoomika Rajput, Ashwani Pandey
      First page: 118
      Abstract: Blazars are known to emit exceptionally variable non-thermal emission over the wide range (from radio to γ-rays) of electromagnetic spectrum. We present here the results of our γ-ray flux and spectral variability study of the blazar Ton 599, which has been recently observed in the γ-ray flaring state. Using 0.1−300 GeV γ-ray data from the Fermi Gamma-ray Space Telescope (hereinafter Fermi), we generated one-day binned light curve of Ton 599 for a period of about one-year from MJD 59,093 to MJD 59,457. During this one year period, the maximum γ-ray flux detected was 2.24 ± 0.25 ×10−6 ph cm−2 s−1 at MJD 59,399.50. We identified three different flux states, namely, epoch A (quiescent), epoch B (pre-flare) and epoch C (main-flare). For each epoch, we calculated the γ-ray flux variability amplitude (Fvar) and found that the source showed largest flux variations in epoch C with Fvar∼ 35%. We modelled the γ-ray spectra for each epoch and found that the Log-parabola model adequately describes the γ-ray spectra for all the three epochs. We estimated the size of the γ-ray emitting region as 1.03 ×1018 cm and determined that the origin of γ-ray radiation, during the main-flare, could be outside of the broad line region.
      Citation: Galaxies
      PubDate: 2021-12-13
      DOI: 10.3390/galaxies9040118
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 119: Lorentz Violation by the Preferred Frame
           Effects and Cosmic and Gamma Ray Propagation

    • Authors: Georgy I. Burde
      First page: 119
      Abstract: The ‘relativity with a preferred frame’, designed to reconcile the relativity principle with the existence of the cosmological preferred frame, incorporates the preferred frame at the level of special relativity (SR) while retaining the fundamental spacetime symmetry, which, in the standard SR, manifests itself as Lorentz invariance. In this paper, the processes, accompanying the propagation of cosmic rays and gamma rays through the background radiation from distant sources to Earth, are considered on the basis of particle dynamics and electromagnetic field dynamics developed within the framework of the ‘relativity with a preferred frame’. Applying the theory to the photopion-production and pair-production processes shows that the modified particle dynamics and electrodynamics lead to measurable signatures in the observed cosmic and gamma-ray spectra which can provide an interpretation of some puzzling features found in the observational data. Other processes responsible for gamma-ray attenuation are considered. It is found, in particular, that electromagnetic cascades, developing on cosmic microwave background and extragalactic background light, may be reduced or suppressed due to the preferred frame effects which should influence the shape of the very high-energy gamma-ray spectra. Other possible observational consequences of the theory, such as the birefringence of light propagating in vacuo and dispersion, are discussed.
      Citation: Galaxies
      PubDate: 2021-12-14
      DOI: 10.3390/galaxies9040119
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 120: Distributed Architectures and Constellations
           for γ-ray Burst Science

    • Authors: Fabrizio Fiore, Norbert Werner, Ehud Behar
      First page: 120
      Abstract: The gravitational wave/γ-ray burst GW/GRB170817 event marked the beginning of the era of multi-messenger astrophysics, in which new observations of Gravitational Waves (GW) are combined with traditional electromagnetic observations from the very same astrophysical source. In the next few years, Advanced LIGO/VIRGO and KAGRA in Japan and LIGO-India will reach their nominal/ultimate sensitivity. In the electromagnetic domain, the Vera C. Rubin Observatory and the Cherenkov Telescope Array (CTA) will come online in the next few years, and they will revolutionize the investigation of transient and variable cosmic sources in the optical and TeV bands. The operation of an efficient X-ray/γ-ray all-sky monitor with good localisation capabilities will play a pivotal role in providing the high-energy counterparts of the GW interferometers and Rubin Observatory, bringing multi-messenger astrophysics to maturity. To reach the required precision in localisation and timeliness for an unpredictable physical event in time and space requires a sensor distribution covering the whole sky. We discuss the potential of large-scale, small-platform-distributed architectures and constellations to build a sensitive X-ray/γ-ray all-sky monitor and the programmatic implications of this, including the set-up of an efficient assembly line for both hardware development and data analysis. We also discuss the potential of a constellation of small platforms operating at other wavelengths (UV/IR) that are capable of repointing quickly to follow-up high-energy transients.
      Citation: Galaxies
      PubDate: 2021-12-16
      DOI: 10.3390/galaxies9040120
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 121: Remnant Radio Galaxy Candidates of Small
           Angular Sizes

    • Authors: Veeresh Singh, Sushant Dutta, Yogesh Wadadekar, C. H. Ishwara-Chandra
      First page: 121
      Abstract: Remnant radio galaxies (RRGs), characterized by the cessation of AGN activity, represent a short-lived last phase of radio galaxy’s life-cycle. Hitherto, searches for RRGs, mainly based on the morphological criteria, have identified large angular size sources resulting into a bias towards the remnants of powerful FR-II radio galaxies. In this study we make the first attempt to perform a systematic search for RRGs of small angular sizes (<30′′) in the XMM−LSS field. By using spectral curvature criterion we discover 48 remnant candidates exhibiting strong spectral curvature i.e.,  α150MHz325MHz−α325MHz1.4GHz≥ 0.5. Spectral characteristics at higher frequency regime (>1.4 GHz) indicate that some of our remnant candidates can depict recurrent AGN activity with an active core. We place an upper limit on the remnant fraction (frem) to be 3.9%, which increases to 5.4% if flux cutoff limit of S150MHz≥ 10 mJy is considered. Our study unveils, hitherto unexplored, a new population of small-size (<200 kpc) remnant candidates that are often found to reside in less dense environments and at higher redshifts (z) > 1.0. We speculate that a relatively shorter active phase and/or low jet power can be plausible reasons for the small size of remnant candidates.
      Citation: Galaxies
      PubDate: 2021-12-16
      DOI: 10.3390/galaxies9040121
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 122: The Photometric and Spectroscopic Properties
           of Remnant and Restarted Radio Galaxies in the Lockman Hole Field

    • Authors: Nika Jurlin, Raffaella Morganti, Natasha Maddox, Marisa Brienza
      First page: 122
      Abstract: Radio galaxies are known to undergo phases of activity, where the stage after the jets have switched off is referred to as the remnant phase. This state can be followed by a restarted phase when the activity reignites. Remnant and restarted radio sources are important for testing models of the evolution of radio active galactic nuclei (AGN) and for understanding the impact the recurrent jet activity has on their host galaxies. Although we now have statistical samples of radio sources in various stages of their life cycle, how this intermittent radio activity is reflected in the optical properties in this sample has not yet been addressed, and is overall a much less studied aspect in the literature. In this work, we use the Wide-field Infrared Survey Explorer and the Sloan Digital Sky Survey (SDSS) photometry, and SDSS spectra to study these properties in a sample of the remnant, candidate restarted, and active radio galaxies selected using the LOw Frequency ARray at 150 MHz in the Lockman Hole extragalactic field. Within the range of radio luminosities and stellar masses studied in this work, we find no difference between the properties of the host galaxy and of the optical emission lines for objects in different phases of their radio life cycle. The vast majority of our radio sources (either remnant, candidate restarted, or comparison sample) are associated with radiatively inefficient optical AGN and red galaxies dominated by old stellar populations. Thus, the radio and emission-line AGN activity appears to be independent and regulated by different mechanisms. This suggests that, at least for the radio luminosities of our sample, the life cycle of the radio may depend on intrinsic reasons, such as the stability of the accretion disc, more than variation in the accretion rate and fuelling of the central black hole.
      Citation: Galaxies
      PubDate: 2021-12-17
      DOI: 10.3390/galaxies9040122
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 9, Pages 123: Review of Solutions to the Cusp-Core Problem
           of the \({\Lambda}\)CDM Model

    • Authors: Antonino Del Popolo, Morgan Le Delliou
      First page: 123
      Abstract: This review aims at proposing to the field an overview of the Cusp-core problem, including a discussion of its advocated solutions, assessing how each can satisfactorily provide a description of central densities. Whether the Cusp-core problem reflects our insufficient grasp on the nature of dark matter, of gravity, on the impact of baryonic interactions with dark matter at those scales, as included in semi-analytical models or fully numerical codes, the solutions to it can point either to the need for a paradigm change in cosmology, or to to our lack of success in ironing out the finer details of the ΛCDM paradigm.
      Citation: Galaxies
      PubDate: 2021-12-18
      DOI: 10.3390/galaxies9040123
      Issue No: Vol. 9, No. 4 (2021)
  • Galaxies, Vol. 10, Pages 1: Promise of Persistent Multi-Messenger
           Astronomy with the Blazar OJ 287

    • Authors: Mauri J. Valtonen, Lankeswar Dey, Achamveedu Gopakumar, Staszek Zola, S. Komossa, Tapio Pursimo, Jose L. Gomez, Rene Hudec, Helen Jermak, Andrei V. Berdyugin
      First page: 1
      Abstract: Successful observations of the seven predicted bremsstrahlung flares from the unique bright blazar OJ 287 firmly point to the presence of a nanohertz gravitational wave (GW) emitting supermassive black hole (SMBH) binary central engine. We present arguments for the continued monitoring of the source in several electromagnetic windows to firmly establish various details of the SMBH binary central engine description for OJ 287. In this article, we explore what more can be known about this system, particularly with regard to accretion and outflows from its two accretion disks. We mainly concentrate on the expected impact of the secondary black hole on the disk of the primary on 3 December 2021 and the resulting electromagnetic signals in the following years. We also predict the times of exceptional fades, and outline their usefulness in the study of the host galaxy. A spectral survey has been carried out, and spectral lines from the secondary were searched for but were not found. The jet of the secondary has been studied and proposals to discover it in future VLBI observations are mentioned. In conclusion, the binary black hole model explains a large number of observations of different kinds in OJ 287. Carefully timed future observations will be able to provide further details of its central engine. Such multi-wavelength and multidisciplinary efforts will be required to pursue multi-messenger nanohertz GW astronomy with OJ 287 in the coming decades.
      Citation: Galaxies
      PubDate: 2021-12-22
      DOI: 10.3390/galaxies10010001
      Issue No: Vol. 10, No. 1 (2021)
  • Galaxies, Vol. 10, Pages 2: Finding Rare Quasars: VLA Snapshot Continuum
           Survey of FRI Quasar Candidates Selected from the LOFAR Two-Metre Sky
           Survey (LoTSS)

    • Authors: Gülay Gürkan, Judith Croston, Martin J. Hardcastle, Vijay Mahatma, Beatriz Mingo, Wendy L. Williams
      First page: 2
      Abstract: The radiative and jet power in active galactic nuclei is generated by accretion of material on to supermassive galactic-centre black holes. For quasars, where the radiative power is by definition very high, objects with high radio luminosities form ∼10 per cent of the population, although it is not clear whether this is a stable phase. Traditionally, quasars with high radio luminosities have been thought to present jets with edge-brightened morphology (Fanaroff-Riley II−FR II) due to the limitations of previous radio surveys (i.e., FRIs were not observed as part of the quasar population). The LOw Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) with its unprecedented sensitivity and resolution covering wide sky areas has enabled the first systematic selection and investigation of quasars with core-brightened morphology (Fanaroff-Riley I−FR). We carried out a Very Large Array (VLA) snapshot survey to reveal inner structures of jets in selected quasar candidates; 15 (25 per cent) out of 60 sources show clear inner jet structures that are diagnostic of FRI jets and 13 quasars (∼22 per cent) show extended structures similar to those of FRI jets. Black hole masses and Eddington ratios do not show a clear difference between FRI and FRII quasars. FRII quasars tend to have higher jet powers than FRI quasars. Our results show that the occurrence of FRI jets in powerful radiatively efficient systems is not common, probably mainly due to two factors: galaxy environment and jet power.
      Citation: Galaxies
      PubDate: 2021-12-22
      DOI: 10.3390/galaxies10010002
      Issue No: Vol. 10, No. 1 (2021)
  • Galaxies, Vol. 10, Pages 3: A Stringent Test of Magnetic Models of Stellar

    • Authors: Guillermo Torres, Gregory A. Feiden, Andrew Vanderburg, Jason L. Curtis
      First page: 3
      Abstract: Main-sequence stars with convective envelopes often appear larger and cooler than predicted by standard models of stellar evolution for their measured masses. This is believed to be caused by stellar activity. In a recent study, accurate measurements were published for the K-type components of the 1.62-day detached eclipsing binary EPIC 219511354, showing the radii and temperatures for both stars to be affected by these discrepancies. This is a rare example of a system in which the age and chemical composition are known, by virtue of being a member of the well-studied open cluster Ruprecht 147 (age~3 Gyr, [Fe/H] = +0.10). Here, we report a detailed study of this system with nonstandard models incorporating magnetic inhibition of convection. We show that these calculations are able to reproduce the observations largely within their uncertainties, providing robust estimates of the strength of the magnetic fields on both stars: 1600 ± 130 G and 1830 ± 150 G for the primary and secondary, respectively. Empirical estimates of the magnetic field strengths based on the measured X-ray luminosity of the system are roughly consistent with these predictions, supporting this mechanism as a possible explanation for the radius and temperature discrepancies.
      Citation: Galaxies
      PubDate: 2021-12-24
      DOI: 10.3390/galaxies10010003
      Issue No: Vol. 10, No. 1 (2021)
  • Galaxies, Vol. 10, Pages 4: Numerical Study of Colliding Winds in Massive

    • Authors: Amit Kashi, Amir Michaelis
      First page: 4
      Abstract: We run a numerical experiment ejecting stellar winds in a very massive binary system measuring the properties of the resulting colliding wind structure and accreted mass onto the companion under different conditions. Colliding massive binaries interact and create a colliding wind structure with a shape that depends on the momentum ratio, orbital motion, distance between the stars, and other factors. We run simulations of a static LBV-WR binary and in each simulation abruptly varying the mass loss rate of the LBV from the fiducial value. The modified wind front propagates and interacts with the previous colliding wind structure, and modifies its shape. We calculate the emitted X-ray from the interaction and investigate the proprieties of the new shape. We derive the mass accretion rate onto the secondary, and find that it depends on the momentum ratio of the winds. We then add orbital velocity that reduces the mass accretion rate, a similar behaviour as the analytical estimates based on modified Bondi–Hoyle–Lyttleton. Creating a large set of simulations like those presented here can allow constraining parameters for specific colliding wind binaries and derive their stellar parameters and orbital solution.
      Citation: Galaxies
      PubDate: 2021-12-28
      DOI: 10.3390/galaxies10010004
      Issue No: Vol. 10, No. 1 (2021)
  • Galaxies, Vol. 10, Pages 5: The Cusp–Core Problem in Gas-Poor
           Dwarf Spheroidal Galaxies

    • Authors: Pierre Boldrini
      First page: 5
      Abstract: This review deals with the inconsistency of inner dark matter density profiles in dwarf galaxies, known as the cusp–core problem. In particular, we aim to focus on gas-poor dwarf galaxies. One of the most promising solutions to this cold dark matter small-scale issue is the stellar feedback, but it seems to be only designed for gas-rich dwarfs. However, in the regime of classical dwarfs, this core mechanism becomes negligible. Therefore, it is required to find solutions without invoking these baryonic processes as dark matter cores tend to persist even for these dwarfs, which are rather dark-matter-dominated. Here, we have presented two categories of solutions. One consists of creating dark matter cores from cusps within cold dark matter by altering the dark matter potential via perturbers. The second category gathers solutions that depict the natural emergence of dark matter cores in alternative theories. Given the wide variety of solutions, it becomes necessary to identify which mechanism dominates in the central region of galaxies by finding observational signatures left by them in order to highlight the true nature of dark matter.
      Citation: Galaxies
      PubDate: 2021-12-30
      DOI: 10.3390/galaxies10010005
      Issue No: Vol. 10, No. 1 (2021)
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