Subjects -> METEOROLOGY (Total: 112 journals)
 Showing 1 - 36 of 36 Journals sorted alphabetically Acta Meteorologica Sinica       (Followers: 3) Advances in Atmospheric Sciences       (Followers: 43) Advances in Climate Change Research       (Followers: 29) Advances in Meteorology       (Followers: 24) Advances in Statistical Climatology, Meteorology and Oceanography       (Followers: 7) Aeolian Research       (Followers: 6) Agricultural and Forest Meteorology       (Followers: 18) American Journal of Climate Change       (Followers: 29) Atmósfera       (Followers: 3) Atmosphere       (Followers: 26) Atmosphere-Ocean       (Followers: 15) Atmospheric and Oceanic Science Letters       (Followers: 11) Atmospheric Chemistry and Physics (ACP)       (Followers: 48) Atmospheric Chemistry and Physics Discussions (ACPD)       (Followers: 15) Atmospheric Environment       (Followers: 73) Atmospheric Environment : X       (Followers: 3) Atmospheric Research       (Followers: 69) Atmospheric Science Letters       (Followers: 36) Boundary-Layer Meteorology       (Followers: 31) Bulletin of Atmospheric Science and Technology       (Followers: 1) Bulletin of the American Meteorological Society       (Followers: 51) Carbon Balance and Management       (Followers: 4) Change and Adaptation in Socio-Ecological Systems       (Followers: 5) Ciencia, Ambiente y Clima       (Followers: 3) Climate       (Followers: 6) Climate and Energy       (Followers: 3) Climate Change Economics       (Followers: 20) Climate Change Research Letters       (Followers: 7) Climate Change Responses       (Followers: 10) Climate Dynamics       (Followers: 44) Climate law       (Followers: 8) Climate of the Past (CP)       (Followers: 5) Climate of the Past Discussions (CPD) Climate Policy       (Followers: 42) Climate Research       (Followers: 6) Climate Resilience and Sustainability       (Followers: 9) Climate Risk Management       (Followers: 5) Climate Services       (Followers: 3) Climate Summary of South Africa       (Followers: 2) Climatic Change       (Followers: 64) Current Climate Change Reports       (Followers: 6) Developments in Atmospheric Science       (Followers: 28) Dynamics and Statistics of the Climate System       (Followers: 5) Dynamics of Atmospheres and Oceans       (Followers: 19) Earth Perspectives - 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Similar Journals
 Monthly Notices of the Royal Astronomical SocietyJournal Prestige (SJR): 2.346 Citation Impact (citeScore): 4Number of Followers: 13      Hybrid journal (It can contain Open Access articles) ISSN (Print) 0035-8711 - ISSN (Online) 1365-2966 Published by Oxford University Press  [415 journals]
• Neutron stars mergers in a stochastic chemical evolution model: impact of
time delay distributions
• Authors: Cavallo L; Cescutti G, Matteucci F.
Pages: 1 - 12
Abstract: ABSTRACTWe study the evolution of the [Eu/Fe] ratio in the Galactic halo by means of a stochastic chemical evolution model considering merging neutron stars as polluters of europium. We improved our previous stochastic chemical evolution model by adding a time delay distribution for the coalescence of the neutron stars, instead of constant delays. The stochastic chemical evolution model can reproduce the trend and the observed spread in the [Eu/Fe] data with neutron star mergers as unique producers if we assume: (i) a delay time distribution ∝t−1.5, (ii) an $M_{\boldsymbol{ Eu}}= 3 \times 10^{-6} \, \boldsymbol{M}_{\odot }$ per event, (iii) progenitors of neutron stars in the range $9\!-\!50\, \boldsymbol{M}_{\odot}$, and (iv) a constant fraction of massive stars in the initial mass function (0.02) that produce neutron star mergers. Our best model is obtained by relaxing point (iv) and assuming a fraction that varies with metallicity. We confirm that the mixed scenario with both merging neutron stars and supernovae as europium producers can provide a good agreement with the data relaxing the constraints on the distribution time delays for the coalescence of neutron stars. Adopting our best model, we also reproduce the dispersion of [Eu/Fe] at a given metallicity, which depends on the fraction of massive stars that produce neutron star mergers. Future high-resolution spectroscopic surveys, such as 4MOST and WEAVE, will produce the necessary statistics to constrain at best this parameter.
PubDate: Wed, 03 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab281
Issue No: Vol. 503, No. 1 (2021)

• The relationship between photometric and spectroscopic oscillation
amplitudes from 3D stellar atmosphere simulations
• Authors: Zhou Y; Nordlander T, Casagrande L, et al.
Pages: 13 - 27
Abstract: ABSTRACTWe establish a quantitative relationship between photometric and spectroscopic detections of solar-like oscillations using ab initio, 3D, hydrodynamical numerical simulations of stellar atmospheres. We present a theoretical derivation as a proof of concept for our method. We perform realistic spectral line formation calculations to quantify the ratio between luminosity and radial velocity amplitude for two case studies: the Sun and the red giant ϵ Tau. Luminosity amplitudes are computed based on the bolometric flux predicted by 3D simulations with granulation background modelled the same way as asteroseismic observations. Radial velocity amplitudes are determined from the wavelength shift of synthesized spectral lines with methods closely resembling those used in Birmingham Solar Oscillations Network (BiSON) and Stellar Oscillations Network Group (SONG) observations. Consequently, the theoretical luminosity to radial velocity amplitude ratios are directly comparable with corresponding observations. For the Sun, we predict theoretical ratios of 21.0 and 23.7 ppm [m s−1]−1 from BiSON and SONG, respectively, in good agreement with observations 19.1 and 21.6 ppm [m s−1]−1. For ϵ Tau, we predict K2 and SONG ratios of 48.4 ppm [m s−1]−1, again in good agreement with observations 42.2 ppm [m s−1]−1, and much improved over the result from conventional empirical scaling relations that give 23.2 ppm [m s−1]−1. This study thus opens the path towards a quantitative understanding of solar-like oscillations, via detailed modelling of 3D stellar atmospheres.
PubDate: Sat, 06 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab337
Issue No: Vol. 503, No. 1 (2021)

• Erratum: The host dark matter haloes of [O ii]  emitters at 0.5
&lt; z &lt; 1.5
• Authors: Gonzalez-Perez V; Comparat J, Norberg P, et al.
Pages: 28 - 30
Abstract: errata, addendamethods: analyticalmethods: numericalgalaxies: evolutiongalaxies: formationcosmology: theory
PubDate: Wed, 10 Mar 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab340
Issue No: Vol. 503, No. 1 (2021)

• The kinematics of globular cluster populations in the E-MOSAICS
simulations and their implications for the assembly history of the Milky
Way
• Authors: Trujillo-Gomez S; Diederik Kruijssen J, Reina-Campos M, et al.
Pages: 31 - 58
Abstract: ABSTRACTWe present a detailed comparison of the Milky Way (MW) globular cluster (GC) kinematics with the 25 MW-mass cosmological simulations from the E-MOSAICS project. While the MW falls within the kinematic distribution of GCs spanned by the simulations, the relative kinematics of its metal-rich ($[\rm {Fe}/\rm {H}]\textgreater -1.2$) versus metal-poor ($[\rm {Fe}/\rm {H}] \lt -1.2$) and inner (r < 8 kpc) versus outer (r > 8 kpc) populations are atypical for its mass. To understand the origins of these features, we perform a comprehensive statistical analysis of the simulations, and find 18 correlations describing the assembly of L* galaxies and their dark matter haloes based on their GC population kinematics. The correlations arise because the orbital distributions of accreted and in situ GCs depend on the masses and accretion redshifts of accreted satellites, driven by the combined effects of dynamical fraction, tidal stripping, and dynamical heating. Because the kinematics of in situ/accreted GCs are broadly traced by the metal-rich/metal-poor and inner/outer populations, the observed GC kinematics are a sensitive probe of galaxy assembly. We predict that relative to the population of L* galaxies, the MW assembled its dark matter and stellar mass rapidly through a combination of in situ star formation, more than a dozen low-mass mergers, and 1.4 ± 1.2 early ($z$ = 3.1 ± 1.3) major mergers. The rapid assembly period ended early, limiting the fraction of accreted stars. We conclude by providing detailed quantitative predictions for the assembly history of the MW.
PubDate: Sat, 06 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab341
Issue No: Vol. 503, No. 1 (2021)

• Using GAMA to probe the impact of small-scale galaxy physics on nonlinear
redshift-space distortions
• Authors: Alam S; Peacock J, Farrow D, et al.
Pages: 59 - 76
Abstract: ABSTRACTWe present improved modelling of the redshift-space distortions (RSDs) of galaxy clustering that arise from peculiar velocities. We create mock galaxy catalogues in the framework of the halo model, using data from the Bolshoi project. These mock galaxy populations are inserted into the haloes with additional degrees of freedom that govern spatial and kinematical biases of the galaxy populations relative to the dark matter. We explore this generalized halo model with an Markov Chain Monte Carlo (MCMC) algorithm, comparing the predictions to data from the Galaxy And Mass Assembly survey, and thus derive one of the first constraints on the detailed kinematic degrees of freedom for satellite galaxies within haloes. With this approach, the distortions of the redshift-space galaxy autocorrelations can be accounted for down to spatial separations close to 10 kpc, opening the prospect of improved RSD measurements of the perturbation growth rate by the inclusion of data from nonlinear scales.
PubDate: Sat, 13 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab409
Issue No: Vol. 503, No. 1 (2021)

• Star formation in ‘the Brick’: ALMA reveals an active protocluster in
the Galactic centre cloud G0.253+0.016
• Authors: Walker D; Longmore S, Bally J, et al.
Pages: 77 - 95
Abstract: ABSTRACTG0.253+0.016, aka ‘the Brick’, is one of the most massive (>105 M⊙) and dense (>104 cm−3) molecular clouds in the Milky Way’s Central Molecular Zone. Previous observations have detected tentative signs of active star formation, most notably a water maser that is associated with a dust continuum source. We present ALMA Band 6 observations with an angular resolution of 0.13 arcsec (1000 AU) towards this ‘maser core’ and report unambiguous evidence of active star formation within G0.253+0.016. We detect a population of eighteen continuum sources (median mass ∼2 M⊙), nine of which are driving bi-polar molecular outflows as seen via SiO (5–4) emission. At the location of the water maser, we find evidence for a protostellar binary/multiple with multidirectional outflow emission. Despite the high density of G0.253+0.016, we find no evidence for high-mass protostars in our ALMA field. The observed sources are instead consistent with a cluster of low-to-intermediate-mass protostars. However, the measured outflow properties are consistent with those expected for intermediate-to-high-mass star formation. We conclude that the sources are young and rapidly accreting, and may potentially form intermediate- and high-mass stars in the future. The masses and projected spatial distribution of the cores are generally consistent with thermal fragmentation, suggesting that the large-scale turbulence and strong magnetic field in the cloud do not dominate on these scales, and that star formation on the scale of individual protostars is similar to that in Galactic disc environments.
PubDate: Sat, 13 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab415
Issue No: Vol. 503, No. 1 (2021)

• Pix2Prof: fast extraction of sequential information from galaxy imagery
via a deep natural language ‘captioning’ model
• Authors: Smith M; Arora N, Stone C, et al.
Pages: 96 - 105
Abstract: ABSTRACTWe present ‘Pix2Prof’, a deep learning model that can eliminate any manual steps taken when measuring galaxy profiles. We argue that a galaxy profile of any sort is conceptually similar to a natural language image caption. This idea allows us to leverage image captioning methods from the field of natural language processing, and so we design Pix2Prof as a float sequence ‘captioning’ model suitable for galaxy profile inference. We demonstrate the technique by approximating a galaxy surface brightness (SB) profile fitting method that contains several manual steps. Pix2Prof processes ∼1 image per second on an Intel Xeon E5-2650 v3 CPU, improving on the speed of the manual interactive method by more than two orders of magnitude. Crucially, Pix2Prof requires no manual interaction, and since galaxy profile estimation is an embarrassingly parallel problem, we can further increase the throughput by running many Pix2Prof instances simultaneously. In perspective, Pix2Prof would take under an hour to infer profiles for 105 galaxies on a single NVIDIA DGX-2 system. A single human expert would take approximately 2 yr to complete the same task. Automated methodology such as this will accelerate the analysis of the next generation of large area sky surveys expected to yield hundreds of millions of targets. In such instances, all manual approaches – even those involving a large number of experts – will be impractical.
PubDate: Sat, 13 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab424
Issue No: Vol. 503, No. 1 (2021)

• Physical and kinematic conditions of the local merging galaxy
NGC 1487
• Authors: Buzzo M; Ziegler B, Amram P, et al.
Pages: 106 - 123
Abstract: ABSTRACTWe present optical VLT/MUSE integral field spectroscopy data of the merging galaxy NGC 1487. We use fitting techniques to study the ionized gas emission of this merger and its main morphological and kinematical properties. We measured flat and sometimes inverted oxygen abundance gradients in the subsystems composing NGC 1487, explained by metal mixing processes common in merging galaxies. We also measured widespread star-forming bursts, indicating that photoionization by stars is the primary ionization source of the galaxy. The kinematic map revealed a rotating pattern in the gas in the northern tail of the system, suggesting that the galaxy may be in the process of rebuilding a disc. The gas located in the central region has larger velocity dispersion (σ ≈ 50 km s−1) than the remaining regions, indicating kinematic heating, possibly owing to the ongoing interaction. Similar trends were, however, not observed in the stellar velocity dispersion map, indicating that the galaxy has not yet achieved equilibrium, and the nebular and stellar components are still kinematically decoupled. Based on all our measurements and findings, and specially on the mass estimates, metallicity gradients, and velocity fields of the system, we propose that NGC 1487 is the result of an ongoing merger event involving smallish dwarf galaxies within a group, in a pre-merger phase, resulting in a relic with mass and physical parameters similar to a dwarf galaxy. Thus, we may be witnessing the formation of a dwarf galaxy by merging of smaller clumps at z = 0.
PubDate: Mon, 15 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab426
Issue No: Vol. 503, No. 1 (2021)

• The highly obscured Seyfert 2 nucleus in NGC 1448 observed with MUSE
• Authors: Menezes R; da Silva P, Steiner J.
Pages: 124 - 141
Abstract: ABSTRACTWe present the analysis of an optical data cube of the central region of NGC 1448, obtained with the Multi Unit Spectroscopic Explorer (MUSE). Chandra X-ray data indicate that the active galactic nucleus (AGN) is not located at the apparent stellar nucleus of the galaxy, but at a projected distance of $1.75\, \pm \, 0.22$ arcsec (139 ± 17 pc). This is probably caused by the high interstellar extinction in the surroundings of the AGN, which corresponds to the true nucleus of the galaxy, as also proposed by previous studies. The morphology and classification of the optical line-emitting regions indicate two ionization cones, around an axis with a position angle of PAcones = −50° ± 7°, with emission-line spectra characteristic of Seyfert galaxies. The stellar and gas kinematics are consistent with a stellar and gas rotating disc around the nucleus, with a velocity amplitude of 125 km s−1. Two probable outflows from the AGN were detected along the region of the two ionization cones. The AGN position does not coincide with the brightest line-emitting region at the centre of NGC 1448. That may be a consequence of the high obscuration from the AGN towards the observer (the AGN is actually Compton thick), mostly caused by a nearly edge-on torus. An additional hypothesis is that the AGN reduced its luminosity, during the last 440 yr, to nearly half of the value in the past. In this case, the brightest line-emitting region corresponds to a ‘light echo’ or a ‘fossil’ of the AGN in the past.
PubDate: Sat, 20 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab478
Issue No: Vol. 503, No. 1 (2021)

• Self-similar adiabatic strong explosion in a medium gravitationally free
falling to a point mass
• Authors: Yalinewich A.
Pages: 142 - 151
Abstract: ABSTRACTWe develop a generalization to the classical Sedov–Taylor explosion where the medium free falls to a point mass at the centre of the explosion. To verify our analytic results, we compare them to a suite of numerical simulations. We find that there exists a critical energy below which, instead of propagating outward the shock stalls and collapses under gravity. Furthermore, we find that the value of the critical energy threshold decreases when the adiabatic index increases and material is more evenly distributed within the shocked region. We apply this model to the problem of a shock bounce in core collapse supernova, in which the proto-neutron star serves as the point mass. The relation between the threshold energy and the distribution of mass in the shock might help explain how turbulence prevents shock stalling and recession in a core-collapse supernova explosion.
PubDate: Fri, 19 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab483
Issue No: Vol. 503, No. 1 (2021)

• Observations of a radio-bright, X-ray obscured GRS 1915+105
• Authors: Motta S; Kajava J, Giustini M, et al.
Pages: 152 - 161
Abstract: ABSTRACTThe Galactic black hole transient GRS 1915+105 is famous for its markedly variable X-ray and radio behaviour, and for being the archetypal galactic source of relativistic jets. It entered an X-ray outburst in 1992 and has been active ever since. Since 2018 GRS 1915+105 has declined into an extended low-flux X-ray plateau, occasionally interrupted by multiwavelength flares. Here, we report the radio and X-ray properties of GRS 1915+105 collected in this new phase, and compare the recent data to historic observations. We find that while the X-ray emission remained unprecedentedly low for most of the time following the decline in 2018, the radio emission shows a clear mode change half way through the extended X-ray plateau in 2019 June: from low flux (∼3 mJy) and limited variability, to marked flaring with fluxes two orders of magnitude larger. GRS 1915+105 appears to have entered a low-luminosity canonical hard state, and then transitioned to an unusual accretion phase, characterized by heavy X-ray absorption/obscuration. Hence, we argue that a local absorber hides from the observer the accretion processes feeding the variable jet responsible for the radio flaring. The radio–X-ray correlation suggests that the current low X-ray flux state may be a signature of a super-Eddington state akin to the X-ray binaries SS433 or V404 Cyg.
PubDate: Wed, 24 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab511
Issue No: Vol. 503, No. 1 (2021)

• Dust transport in protoplanetary discs with wind-driven accretion
• Authors: Hu Z; Bai X.
Pages: 162 - 175
Abstract: ABSTRACTIt has recently been shown that the inner region of protoplanetary discs (PPDs) is governed by wind-driven accretion, and the resulting accretion flow showing complex vertical profiles. Such complex flow structures are further enhanced due to the Hall effect, especially when the background magnetic field is aligned with disc rotation. We investigate how such flow structures impact global dust transport via Monte Carlo simulations, focusing on two scenarios. In the first scenario, the toroidal magnetic field is maximized in the mid-plane, leading to accretion and decretion flows above and below. In the second scenario, the toroidal field changes sign across the mid-plane, leading to an accretion flow at the disc mid-plane, with decretion flows above and below. We find that in both cases, the contribution from additional gas flows can still be accurately incorporated into the advection-diffusion framework for vertically integrated dust transport, with enhanced dust radial (pseudo-)diffusion up to an effective αeff ∼ 10−2 for strongly coupled dust, even when background turbulence is weak α < 10−4. Dust radial drift is also modestly enhanced in the second scenario. We provide a general analytical theory that accurately reproduces our simulation results, thus establishing a framework to model global dust transport that realistically incorporates vertical gas flow structures. We also note that the theory is equally applicable to the transport of chemical species.
PubDate: Wed, 24 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab542
Issue No: Vol. 503, No. 1 (2021)

• Solo dwarfs II: the stellar structure of isolated Local Group dwarf
galaxies
• Authors: Higgs C; McConnachie A, Annau N, et al.
Pages: 176 - 199
Abstract: ABSTRACTThe Solo (Solitary Local) Dwarf Galaxy survey is a volume-limited, wide-field g- and i-band survey of all known nearby (<3 Mpc) and isolated (>300 kpc from the Milky Way or M31) dwarf galaxies. This set of 44 dwarfs is homogeneously analysed for quantitative comparisons to the satellite dwarf populations of the Milky Way and M31. In this paper, an analysis of the 12 closest Solo dwarf galaxies accessible from the Northern hemisphere is presented, including derivation of their distances, spatial distributions, morphology, and extended structures, including their inner integrated light properties and their outer resolved star distributions. All 12 galaxies are found to be reasonably well described by two-dimensional Sérsic functions, although UGC 4879 in particular shows tentative evidence of two distinct components. No prominent extended stellar substructures, which could be signs of either faint satellites or recent mergers, are identified in the outer regions of any of the systems examined.
PubDate: Sat, 09 Jan 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab002
Issue No: Vol. 503, No. 1 (2021)

• The ASAS-SN catalogue of variable stars IX: The spectroscopic properties
of Galactic variable stars
• Authors: Jayasinghe T; Kochanek C, Stanek K, et al.
Pages: 200 - 235
Abstract: ABSTRACTThe All-Sky Automated Survey for Supernovae provides long baseline (∼4 yr) V-band light curves for sources brighter than V≲ 17 mag across the whole sky. We produced V-band light curves for a total of ∼61.5 million sources and systematically searched these sources for variability. We identified ∼426 000 variables, including ∼219 000 new discoveries. Most (${\sim }74{ per\ cent}$) of our discoveries are in the Southern hemisphere. Here, we use spectroscopic information from LAMOST, GALAH, RAVE, and APOGEE to study the physical and chemical properties of these variables. We find that metal-poor eclipsing binaries have orbital periods that are shorter than metal-rich systems at fixed temperature. We identified rotational variables on the main-sequence, red giant branch, and the red clump. A substantial fraction (${\gtrsim }80{ per\ cent}$) of the rotating giants have large $v$rot or large near-ultraviolet excesses also indicative of fast rotation. The rotational variables have unusual abundances suggestive of analysis problems. Semiregular variables tend to be lower metallicity ($\rm [Fe/H]{\sim }-0.5$) than most giant stars. We find that the APOGEE DR16 temperatures of oxygen-rich semiregular variables are strongly correlated with the WRP − WJK colour index for $\rm T_{eff}\lesssim 3800$ K. Using abundance measurements from APOGEE DR16, we find evidence for Mg and N enrichment in the semiregular variables. We find that the Aluminum abundances of the semiregular variables are strongly correlated with the pulsation period, where the variables with $\rm P\gtrsim 60$ d are significantly depleted in Al.
PubDate: Fri, 15 Jan 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab114
Issue No: Vol. 503, No. 1 (2021)

• UOCS – III. UVIT catalogue of open clusters with machine learning-based
membership using Gaia EDR3 astrometry
• Authors: Jadhav V; Pennock C, Subramaniam A, et al.
Pages: 236 - 253
Abstract: ABSTRACTWe present a study of six open clusters (Berkeley 67, King 2, NGC 2420, NGC 2477, NGC 2682, and NGC 6940), using the Ultra Violet Imaging Telescope (UVIT) aboard ASTROSAT and Gaia EDR3. We used combinations of astrometric, photometric, and systematic parameters to train and supervise a machine-learning algorithm along with a Gaussian mixture model for the determination of cluster membership. This technique is robust, reproducible, and versatile in various cluster environments. In this study, the Gaia EDR3 membership catalogues are provided along with classification of the stars as members, candidates, and field in the six clusters. We could detect 200–2500 additional members using our method with respect to previous studies, which helped estimate mean space velocities, distances, number of members and core radii. UVIT photometric catalogues, which include blue stragglers, main-sequence, and red giants are also provided. From UV–Optical colour–magnitude diagrams, we found that majority of the sources in NGC 2682 and a few in NGC 2420, NGC 2477, and NGC 6940 showed excess UV flux. NGC 2682 images have 10 white dwarf detection in far-UV. The far-UV and near-UV images of the massive cluster NGC 2477 have 92 and 576 members, respectively, which will be useful to study the UV properties of stars in the extended turn-off and in various evolutionary stages from main sequence to red clump. Future studies will carry out panchromatic and spectroscopic analysis of noteworthy members detected in this study.
PubDate: Wed, 27 Jan 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab213
Issue No: Vol. 503, No. 1 (2021)

• A tidally tilted sectoral dipole pulsation mode in the eclipsing binary
TIC 63328020
• Authors: Rappaport S; Kurtz D, Handler G, et al.
Pages: 254 - 269
Abstract: ABSTRACTWe report the discovery of the third tidally tilted pulsator, TIC 63328020. Observations with the TESS satellite reveal binary eclipses with an orbital period of 1.1057 d, and δ Scuti-type pulsations with a mode frequency of 21.09533 d−1. This pulsation exhibits a septuplet of orbital sidelobes as well as a harmonic quintuplet. Using the oblique pulsator model, the primary oscillation is identified as a sectoral dipole mode with l = 1, m  = 1. We find the pulsating star to have $M_1 \simeq 2.5 \, {\rm M}_\odot$, $R_1 \simeq 3 \, {\rm R}_\odot$, and Teff, 1 ≃ 8000 K, while the secondary has $M_2 \simeq 1.1 \, {\rm M}_\odot$, $R_2 \simeq 2 \, {\rm R}_\odot$, and Teff, 2 ≃ 5600 K. Both stars appear to be close to filling their respective Roche lobes. The properties of this binary as well as the tidally tilted pulsations differ from the previous two tidally tilted pulsators, HD74423 and CO Cam, in important ways. We also study the prior history of this system with binary evolution models and conclude that extensive mass transfer has occurred from the current secondary to the primary.
PubDate: Tue, 09 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab336
Issue No: Vol. 503, No. 1 (2021)

• Principal component analysis tomography in near-infrared integral field
spectroscopy of young stellar objects – I. Revisiting the high-mass
protostar W33A
• Authors: Navarete F; Damineli A, Steiner J, et al.
Pages: 270 - 291
Abstract: ABSTRACTW33A is a well-known example of a high-mass young stellar object showing evidence of a circumstellar disc. We revisited the K-band NIFS/Gemini North observations of the W33A protostar using principal components analysis tomography and additional post-processing routines. Our results indicate the presence of a compact rotating disc based on the kinematics of the CO absorption features. The position–velocity diagram shows that the disc exhibits a rotation curve with velocities that rapidly decrease for radii larger than 0.1 arcsec (∼250 au) from the central source, suggesting a structure about four times more compact than previously reported. We derived a dynamical mass of 10.0$^{+4.1}_{-2.2}$ $\rm {M}_\odot$ for the ‘disc + protostar’ system, about ∼33 per cent smaller than previously reported, but still compatible with high-mass protostar status. A relatively compact H2 wind was identified at the base of the large-scale outflow of W33A, with a mean visual extinction of ∼63 mag. By taking advantage of supplementary near-infrared maps, we identified at least two other point-like objects driving extended structures in the vicinity of W33A, suggesting that multiple active protostars are located within the cloud. The closest object (Source B) was also identified in the NIFS field of view as a faint point-like object at a projected distance of ∼7000 au from W33A, powering extended K-band continuum emission detected in the same field. Another source (Source C) is driving a bipolar $\rm {H}_2$ jet aligned perpendicular to the rotation axis of W33A.
PubDate: Tue, 09 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab358
Issue No: Vol. 503, No. 1 (2021)

• High-contrast and resolution near-infrared photometry of the core of R136
• Authors: Khorrami Z; Langlois M, Clark P, et al.
Pages: 292 - 311
Abstract: ABSTRACTWe present the sharpest and deepest near-infrared photometric analysis of the core of R136, a newly formed massive star cluster at the centre of the 30 Doradus star-forming region in the Large Magellanic Cloud. We used the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode for the second time with longer exposure time in the H and K filters. Our aim was to (i) increase the number of resolved sources in the core of R136, and (ii) to compare with the first epoch to classify the properties of the detected common sources between the two epochs. Within the field of view (FOV) of 10.8″ × 12.1″ ($2.7\,\text {pc}\times 3.0\, \text {pc}$), we detected 1499 sources in both H and K filters, for which 76 per cent of these sources have visual companions closer than 0.2″. The larger number of detected sources enabled us to better sample the mass function (MF). The MF slopes are estimated at ages of 1, 1.5, and 2 Myr, at different radii, and for different mass ranges. The MF slopes for the mass range of 10–300 M⊙ are about 0.3 dex steeper than the mass range of 3–300 M⊙, for the whole FOV and different radii. Comparing the JHK colours of 790 sources common in between the two epochs, 67 per cent of detected sources in the outer region (r > 3″) are not consistent with evolutionary models at 1–2 Myr and with extinctions similar to the average cluster value, suggesting an origin from ongoing star formation within 30 Doradus, unrelated to R136.
PubDate: Thu, 11 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab388
Issue No: Vol. 503, No. 1 (2021)

• RINGO3 polarimetry of very young ZTF supernovae
• Authors: Maund J; Yang Y, Steele I, et al.
Pages: 312 - 323
Abstract: ABSTRACTThe early phases of the observed evolution of the supernovae (SNe) are expected to be dominated by the shock breakout and ‘flash’ ionization of the surrounding circumstellar medium. This material arises from the last stages of the evolution of the progenitor, such that photometry and spectroscopy of SNe at early times can place vital constraints on the latest and fastest evolutionary phases leading up to stellar death. These signatures are erased by the expansion of the ejecta within ∼5 d after explosion. Here we present the earliest constraints, to date, on the polarization of 10 transients discovered by the Zwicky Transient Facility (ZTF), between 2018 June and 2019 August. Rapid polarimetric follow-up was conducted using the Liverpool Telescope RINGO3 instrument, including three SNe observed within <1 d of detection by the ZTF. The limits on the polarization within the first 5 d of explosion, for all SN types, is generally $\lt 2{ per\ cent}$, implying early asymmetries are limited to axial ratios >0.65 (assuming an oblate spheroidal configuration). We also present polarimetric observations of the Type I Superluminous SN 2018bsz and Type II SN 2018hna, observed around and after maximum light.
PubDate: Sat, 13 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab391
Issue No: Vol. 503, No. 1 (2021)

• Dust entrainment in galactic winds
• Authors: Kannan R; Vogelsberger M, Marinacci F, et al.
Pages: 336 - 343
Abstract: ABSTRACTWinds driven by stellar feedback are an essential part of the galactic ecosystem and are the main mechanism through which low-mass galaxies regulate their star formation. These winds are generally observed to be multiphase with detections of entrained neutral and molecular gas. They are also thought to enrich the circumgalactic medium around galaxies with metals and dust. This ejected dust encodes information about the integrated star formation and outflow history of the galaxy. Therefore it is important to understand how much dust is entrained and driven out of the disc by galactic winds. Here, we demonstrate that stellar feedback is efficient in driving dust-enriched winds and eject enough material to account for the amount of extraplanar dust observed in nearby galaxies. The amount of ejected dust depends on the sites from where they are launched, with dustier galaxies launching more dust-enriched outflows. Moreover, the outflowing cold and dense gas is significantly more dust enriched than the volume filling hot and tenuous material. These results provide an important new insight into the dynamics, structure, and composition of galactic winds and their role in determining the dust content of the extragalactic gas in galaxies.
PubDate: Fri, 12 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab416
Issue No: Vol. 503, No. 1 (2021)

• Quantifying ionospheric effects on global 21-cm observations
• Authors: Shen E; Anstey D, de Lera Acedo E, et al.
Pages: 344 - 353
Abstract: ABSTRACTWe modelled the two major layer of Earth’s ionosphere, the F-layer and the D-layer, by a simplified spatial model with temporal variance to study the chromatic ionospheric effects on global 21-cm observations. From the analyses, we found that the magnitude of the ionospheric disruptions due to ionospheric refraction and absorption can be greater than the expected global 21-cm signal, and the variation of its magnitude can differ, depending on the ionospheric conditions. Within the parameter space adopted in the model, the shape of the global 21-cm signal is distorted after propagating through the ionosphere, while its amplitude is weakened. It is observed that the ionospheric effects do not cancel out over time, and thus should be accounted for in the foreground calibration at each timestep to account for the chromaticity introduced by the ionosphere.
PubDate: Fri, 19 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab429
Issue No: Vol. 503, No. 1 (2021)

• The nearby spiral density-wave structure of the Galaxy: line-of-sight
velocities of the Gaia DR2 OB stars
• Authors: Griv E; Gedalin M, Jiang I.
Pages: 354 - 361
Abstract: ABSTRACTDistances and line-of-sight velocities of 964 Gaia Data Release 2 (DR2) OB stars of Xu et al. within 3 kpc from the Sun and 500 pc from the Galactic mid-plane with accuracies of <50 per cent are selected. The data are used to find small systematic departures of velocities from the mean circular motion for the stars in the solar neighborhood due to the spiral compression-type (Lin–Shu-type) waves, or spiral density waves, e.g. those produced by real instabilities of spontaneous gravity disturbances, a central bar or a companion system. A key point of the study is that our results are consistent with the ones extracted from the asymptotic density-wave theory. Revised parameters of density waves in the solar vicinity of the Galaxy are also provided.
PubDate: Tue, 23 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab455
Issue No: Vol. 503, No. 1 (2021)

• On the dynamical interaction between overshooting convection and an
underlying dipole magnetic field – I. The non-dynamo regime
• Authors: Korre L; Brummell N, Garaud P, et al.
Pages: 362 - 375
Abstract: ABSTRACTMotivated by the dynamics in the deep interiors of many stars, we study the interaction between overshooting convection and the large-scale poloidal fields residing in radiative zones. We have run a suite of 3D Boussinesq numerical calculations in a spherical shell that consists of a convection zone with an underlying stable region that initially compactly contains a dipole field. By varying the strength of the convective driving, we find that, in the less turbulent regime, convection acts as turbulent diffusion that removes the field faster than solely molecular diffusion would do. However, in the more turbulent regime, turbulent pumping becomes more efficient and partially counteracts turbulent diffusion, leading to a local accumulation of the field below the overshoot region. These simulations suggest that dipole fields might be confined in underlying stable regions by highly turbulent convective motions at stellar parameters. The confinement is of large-scale field in an average sense and we show that it is reasonably modelled by mean-field ideas. Our findings are particularly interesting for certain models of the Sun, which require a large-scale, poloidal magnetic field to be confined in the solar radiative zone in order to explain simultaneously the uniform rotation of the latter and the thinness of the solar tachocline.
PubDate: Thu, 18 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab477
Issue No: Vol. 503, No. 1 (2021)

• Did Sgr cause the vertical waves in the solar neighbourhood'
• Authors: Bennett M; Bovy J.
Pages: 376 - 393
Abstract: ABSTRACTThe vertical distribution of stars in the solar neighbourhood is not in equilibrium but contains a wave signature in both density and velocity space originating from a perturbation. With the discovery of the phase-space spiral in Gaia data release (DR) 2, determining the origin of this perturbation has become even more urgent. We develop and test a fast method for calculating the perturbation from a passing satellite on the vertical component of a part of a disc galaxy. This fast method allows us to test a large variety of possible perturbations to the vertical disc very quickly. We apply our method to the range of possible perturbations to the solar neighbourhood stemming from the recent passage of the Sagittarius dwarf galaxy (Sgr), varying its mass, mass profile, and present-day position within their observational uncertainties, and its orbit within different realistic models for the Milky Way’s gravitational potential. We find that we are unable to reproduce the observed asymmetry in the vertical number counts and its concomitant breathing mode in velocity space for any plausible combination of Sgr and Milky Way properties. In all cases, either the amplitude or the perturbation wavelength of the number-count asymmetry and of the oscillations in the mean vertical velocity produced by the passage of Sgr are in large disagreement with the observations from Gaia DR2. We conclude that Sgr cannot have caused the observed oscillations in the vertical disc or the Gaia phase-space spiral.
PubDate: Wed, 24 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab524
Issue No: Vol. 503, No. 1 (2021)

• Compact groups from semi-analytical models of galaxy formation – II.
Different assembly channels
• Authors: Díaz-Giménez E; Zandivarez A, Mamon G.
Pages: 394 - 405
Abstract: ABSTRACTWe study the formation of over 6000 compact groups (CGs) of galaxies identified in mock redshift-space galaxy catalogues built from semi-analytical models of galaxy formation (SAMs) run on the Millennium Simulations. We select CGs of four members in our mock SDSS galaxy catalogues and, for each CG, we trace back in time the real-space positions of the most massive progenitors of their four galaxies. By analysing the evolution of the distance of the galaxy members to the centre of mass of the group, we identify four channels of CG formation. The classification of these assembly channels is performed with an automatic recipe inferred from a preliminary visual inspection and based on the orbit of the galaxy with the fewest number of orbits. Most CGs show late assembly, with the last galaxy arriving on its first or second passage, while only 10–20 per cent form by the gradual contraction of their orbits by dynamical friction, and only a few per cent forming early with little subsequent contraction. However, a SAM from a higher resolution simulation leads to earlier assembly. Assembly histories of CGs also depend on cosmological parameters. At similar resolution, CGs assemble later in SAMs built on parent cosmological simulations of high density parameter. Several observed properties of mock CGs correlate with their assembly history: early-assembling CGs are smaller, with shorter crossing times, and greater magnitude gaps between their brightest two members, and their brightest galaxies have smaller spatial offsets and are more passive.
PubDate: Wed, 24 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab535
Issue No: Vol. 503, No. 1 (2021)

• Multiwavelength monitoring of NGC 1275 over a decade: evidence of a shift
in synchrotron peak frequency and long-term multiband flux increase
• Authors: Gulati S; Bhattacharya D, Bhattacharyya S, et al.
Pages: 446 - 457
Abstract: ABSTRACTWe carried out a detailed study of the temporal and broad-band spectral behaviour of one of the brightest misaligned active galaxies in γ-rays, NGC 1275, utilizing 11 years of Fermi data and the available Swift and AstroSat observations. Based on the cumulative flux distribution of the γ-ray light curve, we identified four distinct activity states and noticed an increase in the baseline flux during the first three states. A similar nature of increase in the average flux was also noticed in the X-ray and UV bands. Strong flaring activity in γ-rays was noticed in the fourth state. The source was observed twice by AstroSat for shorter intervals (∼days) during longer observing (∼years) states 3 and 4. During the AstroSat observing periods, the source γ-ray flux was higher than the average flux observed during longer duration states. The increase in average baseline flux from state 1 to state 3 can be explained by considering a corresponding increase of jet particle normalization. The inverse Comptonization of synchrotron photons explained the average X-ray and γ-ray emission by jet electrons during the first three longer duration states. However, during the shorter duration AstroSat observing periods, a shift of synchrotron peak frequency was noticed, and the synchrotron emission of jet electrons explained the observed X-ray flux well.
PubDate: Sat, 13 Mar 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab244
Issue No: Vol. 503, No. 1 (2021)

• Capture rate of weakly interacting massive particles (WIMPs) in binary
star systems
• Authors: Hassani E; Ebadi H, Pazhouhesh R, et al.
Pages: 458 - 471
Abstract: ABSTRACTThe distribution of dark matter (DM) inside galaxies is not uniform. Near the central regions, its density is the highest. Then, it is logical to suppose that, inside galaxies, DM affects the physics of stars in central regions more than outer regions. Besides, current stellar evolutionary models did not consider DM effects in their assumptions. To consider DM effects, at first one must estimate how much DM a star contains. The capture rate (CR) of DM particles by individual stars was investigated already in the literature. In this work, we discuss how CR can be affected when stars are members of binary star systems (BSSs; instead of studying them individually). When a star is a member of a BSS, its speed changes periodically due to the elliptical motion around its companion star. In this work, we investigated CR by BSSs in different BSS configurations. In the end, we discussed observational signatures that can be attributed to the DM effects in BSSs.
PubDate: Fri, 29 Jan 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab256
Issue No: Vol. 503, No. 1 (2021)

• Multiwavelength observations of the Galactic X-ray binaries IGR
J20155+3827 and Swift J1713.4−4219
• Authors: Onori F; Fiocchi M, Masetti N, et al.
Pages: 472 - 483
Abstract: ABSTRACTIn recent years, thanks to the continuous surveys performed by INTEGRAL and Swift satellites, our knowledge of the hard X-ray/soft gamma-ray sky has greatly improved. As a result it is now populated with about 2000 sources, both Galactic and extra-galactic, mainly discovered by IBIS and BAT instruments. Many different follow-up campaigns have been successfully performed by using a multiwavelength approach, shedding light on the nature of a number of these new hard X-ray sources. However, a fraction are still of an unidentified nature. This is mainly due to the lack of lower energy observations, which usually deliver a better constrained position for the sources, and the unavailability of the key observational properties, needed to obtain a proper physical characterization. Here, we report on the classification of two poorly studied Galactic X-ray transients IGR J20155+3827 and Swift J1713.4−4219, for which the combination of new and/or archival X-ray and optical/NIR (near-infrared) observations have allowed us to pinpoint their nature. In particular, thanks to XMM–Newton archival data together with new optical spectroscopic and archival optical/NIR photometric observations, we have been able to classify IGR J20155+3827 as a distant HMXB (high-mass X-ray binaries). The new INTEGRAL and Swift data collected during the 2019 X-ray outburst of Swift J1713.4−4219, in combination with the archival optical/NIR observations, suggest an LMXB (low-mass X-ray binaries) classification for this source.
PubDate: Fri, 05 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab315
Issue No: Vol. 503, No. 1 (2021)

• Informative Bayesian model selection for RR Lyrae star classifiers
• Authors: Pérez-Galarce F; Pichara K, Huijse P, et al.
Pages: 484 - 497
Abstract: ABSTRACTMachine learning has achieved an important role in the automatic classification of variable stars, and several classifiers have been proposed over the last decade. These classifiers have achieved impressive performance in several astronomical catalogues. However, some scientific articles have also shown that the training data therein contain multiple sources of bias. Hence, the performance of those classifiers on objects not belonging to the training data is uncertain, potentially resulting in the selection of incorrect models. Besides, it gives rise to the deployment of misleading classifiers. An example of the latter is the creation of open-source labelled catalogues with biased predictions. In this paper, we develop a method based on an informative marginal likelihood to evaluate variable star classifiers. We collect deterministic rules that are based on physical descriptors of RR Lyrae stars, and then, to mitigate the biases, we introduce those rules into the marginal likelihood estimation. We perform experiments with a set of Bayesian logistic regressions, which are trained to classify RR Lyraes, and we found that our method outperforms traditional non-informative cross-validation strategies, even when penalized models are assessed. Our methodology provides a more rigorous alternative to assess machine learning models using astronomical knowledge. From this approach, applications to other classes of variable stars and algorithmic improvements can be developed.
PubDate: Fri, 05 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab320
Issue No: Vol. 503, No. 1 (2021)

• Formation of counter-rotating and highly eccentric massive black hole
binaries in galaxy mergers
• Authors: Nasim I; Petrovich C, Nasim A, et al.
Pages: 498 - 510
Abstract: ABSTRACTSupermassive black hole (SMBH) binaries represent the main target for missions such as the Laser Interferometer Space Antenna and Pulsar Timing Arrays. The understanding of their dynamical evolution prior to coalescence is therefore crucial to improving detection strategies and for the astrophysical interpretation of the gravitational wave data. In this paper, we use high-resolution N-body simulations to model the merger of two equal-mass galaxies hosting a central SMBH. In our models, all binaries are initially prograde with respect to the galaxy sense of rotation. But, binaries that form with a high eccentricity, e ≳ 0.7, quickly reverse their sense of rotation and become almost perfectly retrograde at the moment of binary formation. The evolution of these binaries proceeds towards larger eccentricities, as expected for a binary hardening in a counter-rotating stellar distribution. Binaries that form with lower eccentricities remain prograde and at comparatively low eccentricities. We study the origin of the orbital flip by using an analytical model that describes the early stages of binary evolution. This model indicates that the orbital plane flip is due to the torque from the triaxial background mass distribution that naturally arises from the galactic merger process. Our results imply the existence of a population of SMBH binaries with a high eccentricity and could have significant implications for the detection of the gravitational wave signal emitted by these systems.
PubDate: Tue, 09 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab351
Issue No: Vol. 503, No. 1 (2021)

• Dust evolution in zoom-in cosmological simulations of galaxy formation
• Authors: Granato G; Ragone-Figueroa C, Taverna A, et al.
Pages: 511 - 532
Abstract: ABSTRACTWe present cosmological zoom-in hydrodynamical simulations for the formation of disc galaxies, implementing dust evolution and dust promoted cooling of hot gas. We couple an improved version of our previous treatment of dust evolution, which adopts the two-size approximation to estimate the grain-size distribution, with the MUPPI star formation and feedback subresolution model. Our dust evolution model follows carbon and silicate dust separately. To distinguish differences induced by the chaotic behaviour of simulations from those genuinely due to different simulation set-up, we run each model six times, after introducing tiny perturbations in the initial conditions. With this method, we discuss the role of various dust-related physical processes and the effect of a few possible approximations adopted in the literature. Metal depletion and dust cooling affect the evolution of the system, causing substantial variations in its stellar, gas, and dust content. We discuss possible effects on the Spectral Energy Distribution of the significant variations of the size distribution and chemical composition of grains, as predicted by our simulations during the evolution of the galaxy. We compare dust surface density, dust-to-gas ratio, and small-to-large grain mass ratio as a function of galaxy radius and gas metallicity predicted by our fiducial run with recent observational estimates for three disc galaxies of different masses. The general agreement is good, in particular taking into account that we have not adjusted our model for this purpose.
PubDate: Tue, 09 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab362
Issue No: Vol. 503, No. 1 (2021)

• The phenomenology of dynamical neutron star tides
• Authors: Andersson N; Pnigouras P.
Pages: 533 - 539
Abstract: ABSTRACTWe introduce a phenomenological, physically motivated, model for the effective tidal deformability of a neutron star, adding the frequency dependence (associated with the star’s fundamental mode of oscillation) that comes into play during the late stages of the binary inspiral. Testing the model against alternative descriptions, we demonstrate that it provides an accurate representation of the dynamical tide up to close to merger. The simplicity of the prescription makes it an attractive alternative for a gravitational-wave data analysis implementation, facilitating an inexpensive construction of a large number of templates covering the relevant parameter space.
PubDate: Wed, 10 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab371
Issue No: Vol. 503, No. 1 (2021)

• Extended fast action minimization method: application to SDSS-DR12
combined sample
• Authors: Sarpa E; Veropalumbo A, Schimd C, et al.
Pages: 540 - 556
Abstract: ABSTRACTWe present the first application of the extended Fast Action Minimization method (eFAM) to a real data set, the SDSS-DR12 Combined Sample, to reconstruct galaxies orbits back-in-time, their two-point correlation function (2PCF) in real-space, and enhance the baryon acoustic oscillation (BAO) peak. For this purpose, we introduce a new implementation of eFAM that accounts for selection effects, survey footprint, and galaxy bias. We use the reconstructed BAO peak to measure the angular diameter distance, $D_\mathrm{A}(z)r^\mathrm{fid}_\mathrm{s}/r_\mathrm{s}$, and the Hubble parameter, $H(z)r_\mathrm{s}/r^\mathrm{fid}_\mathrm{s}$, normalized to the sound horizon scale for a fiducial cosmology $r^\mathrm{fid}_\mathrm{s}$, at the mean redshift of the sample z = 0.38, obtaining $D_\mathrm{A}(z=0.38)r^\mathrm{fid}_\mathrm{s}/r_\mathrm{s}=1090\pm 29$(Mpc)−1, and $H(z=0.38)r_\mathrm{s}/r^\mathrm{fid}_\mathrm{s}=83\pm 3$(km s−1 Mpc−1), in agreement with previous measurements on the same data set. The validation tests, performed using 400 publicly available SDSS-DR12 mock catalogues, reveal that eFAM performs well in reconstructing the 2PCF down to separations of ∼25h−1Mpc, i.e. well into the non-linear regime. Besides, eFAM successfully removes the anisotropies due to redshift-space distortion (RSD) at all redshifts including that of the survey, allowing us to decrease the number of free parameters in the model and fit the full-shape of the back-in-time reconstructed 2PCF well beyond the BAO peak. Recovering the real-space 2PCF, eFAM improves the precision on the estimates of the fitting parameters. When compared with the no-reconstruction case, eFAM reduces the uncertainty of the Alcock-Paczynski distortion parameters α⊥ and α∥ of about 40 per cent and that on the non-linear damping scale Σ∥ of about 70 per cent. These results show that eFAM can be successfully applied to existing redshift galaxy catalogues and should be considered as a reconstruction tool for next-generation surveys alternative to popular methods based on the Zel’dovich approximation.
PubDate: Wed, 10 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab378
Issue No: Vol. 503, No. 1 (2021)

• Smooth stochastic density field reconstruction
• Authors: Aragon-Calvo M.
Pages: 557 - 562
Abstract: ABSTRACTWe introduce a method for generating a continuous, mass-conserving and high-order differentiable density field from a discrete point distribution such as particles or haloes from an N-body simulation or galaxies from a spectroscopic survey. The method consists on generating an ensemble of point realizations by perturbing the original point set following the geometric constraints imposed by the Delaunay tessellation in the vicinity of each point in the set. By computing the mean field of the ensemble we are able to significantly reduce artefacts arising from the Delaunay tessellation in poorly sampled regions while conserving the features in the point distribution. Our implementation is based on the Delaunay Tessellation Field Estimation (DTFE) method; however, other tessellation techniques are possible. The method presented here shares the same advantages of the DTFE method such as self-adaptive scale, mass conservation, and continuity, while being able to reconstruct even the faintest structures of the point distribution usually dominated by artefacts in Delaunay-based methods.Additionally, we also present preliminary results of an application of this method to image denoising and artefact removal, highlighting the broad applicability of the technique introduced here.
PubDate: Thu, 11 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab403
Issue No: Vol. 503, No. 1 (2021)

• The tune of the Universe: the role of plasma in tests of strong-field
gravity
• Authors: Cardoso V; Guo W, Macedo C, et al.
Pages: 563 - 573
Abstract: ABSTRACTGravitational-wave (GW) astronomy, together with precise pulsar timing and long baseline interferometry, is changing our ability to perform tests of fundamental physics with astrophysical observations. Some of these tests are based on electromagnetic (EM) probes or electrically charged bodies, and assume an empty Universe. However, the cosmos is filled with plasma, a dilute medium which prevents the propagation of low-frequency, small-amplitude EM waves. We show that the plasma hinders our ability to perform some strong-field gravity tests, in particular: (i) nonlinear plasma effects dramatically quench plasma-driven super-radiant instabilities; (ii) the contribution of EM emission to the inspiral of charged black-hole binaries is strongly suppressed; (iii) EM-driven secondary modes, although present in the spectrum of charged black holes, are excited to negligible amplitude in the GW ringdown signal. The last two effects are relevant also in the case of massive fields that propagate in vacuum and can jeopardize tests of modified theories of gravity containing massive degrees of freedom.
PubDate: Thu, 11 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab404
Issue No: Vol. 503, No. 1 (2021)

• A self-supervised, physics-aware, Bayesian neural network architecture for
modelling galaxy emission-line kinematics
• Authors: Dawson J; Davis T, Gomez E, et al.
Pages: 574 - 585
Abstract: ABSTRACTIn the upcoming decades, large facilities, such as the SKA, will provide resolved observations of the kinematics of millions of galaxies. In order to assist in the timely exploitation of these vast data sets, we explore the use of a self-supervised, physics-aware neural network capable of Bayesian kinematic modelling of galaxies. We demonstrate the network’s ability to model the kinematics of cold gas in galaxies with an emphasis on recovering physical parameters and accompanying modelling errors. The model is able to recover rotation curves, inclinations and disc scale lengths for both CO and H i data which match well with those found in the literature. The model is also able to provide modelling errors over learned parameters, thanks to the application of quasi-Bayesian Monte Carlo dropout. This work shows the promising use of machine learning, and in particular, self-supervised neural networks, in the context of kinematically modelling galaxies. This work represents the first steps in applying such models for kinematic fitting and we propose that variants of our model would seem especially suitable for enabling emission-line science from upcoming surveys with e.g. the SKA, allowing fast exploitation of these large data sets.
PubDate: Sat, 13 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab427
Issue No: Vol. 503, No. 1 (2021)

• Radiative shocks around super-eddington accreting black holes
• Authors: Okuda T; Singh C.
Pages: 586 - 593
Abstract: ABSTRACTWe examine radiative standing shocks in advective accretion flows around stellar-mass black holes by 2D radiation hydrodynamic simulations, focusing on the super-Eddington accreting flow. Under a set of input flow parameters responsible for the standing shock, the shock location on the equator decreases towards the event horizon with an increasing accretion rate. The optically thin and hot gas in the narrow funnel region along the rotational axis changes gradually into a dense and optically thick state with the increasingly dense gas transported from the base of the radiative shock near the equator. As a result, the luminosity becomes as high as ∼1040 erg s−1, and the radiation shows a strongly anisotropic distribution around the rotational axis and then very low edge-on luminosity as ∼1036 erg s−1. The mass outflow rate from the outer boundary is high as ∼10−5 and $10^{-4} \, \mathrm{M}_{\odot }$ yr−1 but most of the outflow is originated through the radial outer boundary and may be observed over a wide wind region. The models show approximately blackbody spectra with a temperature of 5 × 106–3 × 107 K at the vertical outer boundary surface. The radiative shock models with the super-Eddington luminosities show a possible model for the superaccretor SS 433 and ultraluminous X-ray sources with stellar-mass black holes.
PubDate: Sat, 13 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab428
Issue No: Vol. 503, No. 1 (2021)

• Are we observing an NSC in course of formation in the NGC 4654
galaxy'
• Authors: Schiavi R; Capuzzo-Dolcetta R, Georgiev I, et al.
Pages: 594 - 602
Abstract: ABSTRACTWe use direct N-body simulations to explore some possible scenarios for the future evolution of two massive clusters observed towards the centre of NGC 4654, a spiral galaxy with mass similar to that of the Milky Way. Using archival HST data, we obtain the photometric masses of the two clusters, M = 3 × 105 M⊙ and M = 1.7 × 106 M⊙, their half-light radii, Reff ∼ 4 pc and Reff ∼ 6 pc, and their projected distances from the photometric centre of the galaxy (both <22 pc). The knowledge of the structure and separation of these two clusters (∼24 pc) provides a unique view for studying the dynamics of a galactic central zone hosting massive clusters. Varying some of the unknown cluster orbital parameters, we carry out several N-body simulations showing that the future evolution of these clusters will inevitably result in their merger. We find that, mainly depending on the shape of their relative orbit, they will merge into the galactic centre in less than 82 Myr. In addition to the tidal interaction, a proper consideration of the dynamical friction braking would shorten the merging times up to few Myr. We also investigate the possibility to form a massive nuclear star cluster (NSC) in the centre of the galaxy by this process. Our analysis suggests that for low-eccentricity orbits, and relatively long merger times, the final merged cluster is spherical in shape, with an effective radius of few parsecs and a mass within the effective radius of the order of $10^5\, \mathrm{M_{\odot }}$. Because the central density of such a cluster is higher than that of the host galaxy, it is likely that this merger remnant could be the likely embryo of a future NSC.
PubDate: Thu, 18 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab458
Issue No: Vol. 503, No. 1 (2021)

• The former companion of hyper-velocity star S5-HVS1
• Authors: Lu W; Fuller J, Raveh Y, et al.
Pages: 603 - 613
Abstract: ABSTRACTThe hyper-velocity star S5-HVS1, ejected 5 Myr ago from the Galactic Centre at 1800 km s−1, was most likely produced by tidal break-up of a tight binary by the supermassive black hole SgrA*. Taking a Monte Carlo approach, we show that the former companion of S5-HVS1 was likely a main-sequence star between 1.2 and 6 M⊙ and was captured into a highly eccentric orbit with pericentre distance in the range of 1–10 au and semimajor axis about 103 au. We then explore the fate of the captured star. We find that the heat deposited by tidally excited stellar oscillation modes leads to runaway disruption if the pericentre distance is smaller than about $3\rm \, au$. Over the past 5 Myr, its angular momentum has been significantly modified by orbital relaxation, which may stochastically drive the pericentre inwards below $3\rm \, au$ and cause tidal disruption. We find an overall survival probability in the range 5 per cent to 50 per cent, depending on the local relaxation time in the close environment of the captured star, and the initial pericentre at capture. The pericentre distance of the surviving star has migrated to 10–100 au, making it potentially the most extreme member of the S-star cluster. From the ejection rate of S5-HVS1-like stars, we estimate that there may currently be a few stars in such highly eccentric orbits. They should be detectable (typically $K_{\rm s}\lesssim 18.5\,$ mag) by the GRAVITY instrument and by future Extremely Large Telescopes and hence provide an extraordinary probe of the spin of SgrA*.
PubDate: Wed, 17 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab459
Issue No: Vol. 503, No. 1 (2021)

• Fast infrared variability from the black hole candidate MAXI J1535−571
and tight constraints on the modelling
• Authors: Vincentelli F; Casella P, Russell D, et al.
Pages: 614 - 624
Abstract: ABSTRACTWe present the results regarding the analysis of the fast X-ray/infrared (IR) variability of the black hole transient MAXI J1535−571. The data studied in this work consist of two strictly simultaneous observations performed with XMM–Newton (X-rays: 0.7–10 keV), VLT/HAWK-I (Ks band, 2.2 μm) and VLT/VISIR (M and PAH2_2 bands, 4.85 and 11.88 μm, respectively). The cross-correlation function between the X-ray and near-IR light curves shows a strong asymmetric anticorrelation dip at positive lags. We detect a near-IR QPO (2.5σ) at 2.07 ± 0.09 Hz simultaneously with an X-ray QPO at approximately the same frequency (f0 = 2.25 ± 0.05). From the cross-spectral analysis, a lag consistent with zero was measured between the two oscillations. We also measure a significant correlation between the average near-IR and mid-IR fluxes during the second night, but find no correlation on short time-scales. We discuss these results in terms of the two main scenarios for fast IR variability (hot inflow and jet powered by internal shocks). In both cases, our preliminary modelling suggests the presence of a misalignment between the disc and jet.
PubDate: Fri, 19 Feb 2021 00:00:00 GMT
DOI: 10.1093/mnras/stab475
Issue No: Vol. 503, No. 1 (2021)

• Cosmological perturbations for two cold fluids in ΛCDM
• Authors: Rampf C; Uhlemann C, Hahn O.
Pages: 406 - 425
Abstract: ABSTRACTThe cosmic large-scale structure of our Universe is comprised of baryons and cold dark matter (CDM). Yet it is customary to treat these two components as a combined single-matter fluid with vanishing pressure, which is justified only for sufficiently large scales and late times. Here, we go beyond the single-fluid approximation and develop the perturbation theory for two gravitationally coupled fluids while still assuming vanishing pressure. We mostly focus on perturbative expansions in powers of D (or D+), the linear structure growth of matter in a ΛCDM Universe with cosmological constant Λ. We derive in particular (1) explicit recursion relations for the two fluid densities, (2) complementary all-order results in the Lagrangian-coordinates approach, as well as (3) the associated component wavefunctions in a semiclassical approach to cosmic large-scale structure. In our companion paper, we apply these new theoretical results to generate novel higher order initial conditions for cosmological hydrodynamical simulations.
PubDate: Fri, 11 Dec 2020 00:00:00 GMT
DOI: 10.1093/mnras/staa3605
Issue No: Vol. 503, No. 1 (2020)

• Higher order initial conditions for mixed baryon–CDM simulations
• Authors: Hahn O; Rampf C, Uhlemann C.
Pages: 426 - 445
Abstract: ABSTRACTWe present a novel approach to generate higher order initial conditions (ICs) for cosmological simulations that take into account the distinct evolution of baryons and dark matter. We focus on the numerical implementation and the validation of its performance, based on both collisionless N-body simulations and full hydrodynamic Eulerian and Lagrangian simulations. We improve in various ways over previous approaches that were limited to first-order Lagrangian perturbation theory (LPT). Specifically, we (1) generalize nth-order LPT to multifluid systems, allowing 2LPT or 3LPT ICs for two-fluid simulations, (2) employ a novel propagator perturbation theory to set up ICs for Eulerian codes that are fully consistent with 1LPT or 2LPT, (3) demonstrate that our ICs resolve previous problems of two-fluid simulations by using variations in particle masses that eliminate spurious deviations from expected perturbative results, (4) show that the improvements achieved by going to higher order PT are comparable to those seen for single-fluid ICs, and (5) demonstrate the excellent (i.e. few per cent level) agreement between Eulerian and Lagrangian simulations, once high-quality initial conditions are used. The rigorous development of the underlying perturbation theory is presented in a companion paper. All presented algorithms are implemented in the monofonic music-2 package that we make publicly available.
PubDate: Fri, 11 Dec 2020 00:00:00 GMT
DOI: 10.1093/mnras/staa3773
Issue No: Vol. 503, No. 1 (2020)

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