Subjects -> METEOROLOGY (Total: 106 journals)
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 Monthly Notices of the Royal Astronomical SocietyJournal Prestige (SJR): 2.346 Citation Impact (citeScore): 4Number of Followers: 15      Hybrid journal (It can contain Open Access articles) ISSN (Print) 0035-8711 - ISSN (Online) 1365-2966 Published by Oxford University Press  [424 journals]
• Growing the first galaxies’ merger trees

Pages: 3201 - 3220
Abstract: ABSTRACTModelling the growth histories of specific galaxies often involves generating the entire population of objects that arise in a given cosmology and selecting systems with appropriate properties. This approach is highly inefficient when targeting rare systems such as the extremely luminous high-redshift galaxy candidates detected by JWST. Here, we present a novel framework for generating merger trees with branches that are guaranteed to achieve a desired halo mass at a chosen redshift. This method augments extended Press Schechter theory solutions with constrained random processes known as Brownian bridges and is implemented in the open-source semi-analytic model galacticus. We generate ensembles of constrained merger trees to predict the growth histories of seven high-redshift JWST galaxy candidates, finding that these systems most likely merge ≈2 Gyr after the observation epoch and occupy haloes of mass ≳1014 M⊙ today. These calculations are thousands of times more efficient than existing methods, are analytically controlled, and provide physical insights into the evolution of haloes with rapid early growth. Our constrained merger tree implementation is publicly available at https://github.com/galacticusorg/galacticus.
PubDate: Thu, 02 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Multipole expansion for 21 cm intensity mapping power spectrum:
Forecasted cosmological parameters estimation for the SKA observatory

Pages: 3221 - 3236
Abstract: ABSTRACTThe measurement of the large-scale distribution of neutral hydrogen in the late Universe, obtained with radio telescopes through the hydrogen 21 cm line emission, has the potential to become a key cosmological probe in the upcoming years. We explore the constraining power of 21 cm intensity mapping observations on the full set of cosmological parameters that describe the ΛCDM model. We assume a single-dish survey for the SKA Observatory and simulate the 21 cm linear power spectrum monopole and quadrupole within six redshift bins in the range $z$ = 0.25–3. Forecasted constraints are computed numerically through Markov Chain Monte Carlo techniques. We extend the sampler CosmoMC by implementing the likelihood function for the 21 cm power spectrum multipoles. We assess the constraining power of the mock data set alone and combined with Planck 2018 CMB observations. We find that 21 cm multipoles observations alone are enough to obtain constraints on the cosmological parameters comparable with other probes. Combining the 21 cm data set with CMB observations results in significantly reduced errors on all the cosmological parameters. The strongest effect is on Ωch2 and H0, for which the error is reduced by almost a factor four. The percentage errors we estimate are $\sigma _{\Omega _ch^2} = 0.25~{{\ \rm per\ cent}}$ and $\sigma _{H_0} = 0.16~{{\ \rm per\ cent}}$, to be compared with the Planck only results $\sigma _{\Omega _ch^2} = 0.99~{{\ \rm per\ cent}}$ and $\sigma _{H_0} = 0.79~{{\ \rm per\ cent}}$. We conclude that 21 cm SKAO observations will provide a competitive cosmological probe, complementary to CMB and, thus, pivotal for gaining statistical significance on the cosmological parameters constraints, allowing a stress test for the current cosmological model.
PubDate: Mon, 06 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Advection-dominated accretion flow for the varied transition luminosities
in black hole X-ray binaries

Pages: 3237 - 3246
Abstract: ABSTRACTObservationally, two main spectral states, i.e. the low/hard state and the high/soft state, are identified in black hole X-ray binaries (BH-XRBs). Meanwhile, the transitions between the two states are often observed. In this paper, we re-investigate the transition luminosities in the framework of the self-similar solution of the advection-dominated accretion flow (ADAF). Specifically, we search for the critical mass accretion rate $\dot{m}_{\rm crit}$ of ADAF for different radii r, respectively. It is found that $\dot{m}_{\rm crit}$ decreases with decreasing r. By testing the effects of BH mass m, the magnetic parameter β and the viscosity parameter α, it is found that only α has significant effects on $\dot{m}_{\rm crit}\text{--}r$ relation. We define the minimum $\dot{m}_{\rm crit}$ (roughly at the innermost stable circular orbit) as the hard-to-soft transition rate $\dot{m}_{\rm tr:H\text{--} S}$, above which BH will gradually transit from the low/hard state to the high/soft state, and $\dot{m}_{\rm crit}$ at 30 Schwarzschild radii as the soft-to-hard transition rate $\dot{m}_{\rm tr:S\rightarrow H}$, below which BH will gradually transit from the high/soft state to the low/hard state. We derive fitting formulae of $\dot{m}_{\rm tr:H\rightarrow S}$ and $\dot{m}_{\rm tr:S\rightarrow H}$ as functions of α, respectively. By comparing with observations, it is found that the mean value of α are α ∼ 0.85 and α ∼ 0.33 for the hard-to-soft transition and the soft-to-hard transition, respectively, which indicates that two classes of α are needed for explaining the hysteresis effect during the state transition. Finally, we argue that such a constrained α may provide valuable clues for further exploring the accretion physics in BH-XRBs.
PubDate: Mon, 13 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The connection between the escape of ionizing radiation and galaxy
properties at z ∼ 3 in the Keck Lyman continuum spectroscopic survey

Pages: 3247 - 3259
Abstract: ABSTRACTThe connection between the escape fraction of ionizing radiation (fesc) and the properties of galaxies, such as stellar mass ($\rm M_{\rm *}$), age, star-formation rate (SFR), and dust content, are key inputs for reionization models, but many of these relationships remain untested at high redshift. We present an analysis of a sample of 96 $z$ ∼ 3 galaxies from the Keck Lyman Continuum Spectroscopic Survey (KLCS). These galaxies have both sensitive Keck/LRIS spectroscopic measurements of the Lyman continuum (LyC) region, and multiband photometry that places constraints on stellar population parameters. We construct composite spectra from subsamples binned as a function of galaxy property and quantify the ionizing-photon escape for each composite. We find a significant anti-correlation between fesc and $\rm M_{\rm *}$, consistent with predictions from cosmological zoom-in simulations. We also find significant anti-correlation between fesc and E(B−V), encoding the underlying physics of LyC escape in our sample. We also find no significant correlation between fesc and either stellar age or specific SFR (= SFR/$\rm M_{\rm *}$), challenging interpretations that synchronize recent star formation and favorable conditions for ionizing escape. The galaxy properties now shown to correlate with fesc in the KLCS are Lyα equivalent width, UV Luminosity, $\rm M_{\rm *}$, SFR, and E(B−V), but not age or sSFR. This comprehensive analysis of galaxy properties and LyC escape at high redshift will be used to guide future models and observations of the reionization epoch.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Spatially resolved observations of outflows in the radio loud AGN of
UGC 8782

Pages: 3260 - 3272
Abstract: ABSTRACTWe use optical integral field spectroscopy (IFU) to study the gas emission structure and kinematics in the inner 3.4 × 4.9 kpc2 region of the galaxy UGC 8782 (3C 293), host of a radio loud active galactic nucleus (AGN). The observations were performed with the Gemini-North multi-object spectrograph (GMOS)-IFU on the Gemini North telescope, resulting in a spatial resolution of ∼725 pc at the distance of the galaxy. While the stars present ordered rotation following the orientation of the large-scale disc, the gas shows a disturbed kinematics. The emission-line profiles present two kinematic components: a narrow (σ ≲ 200 km s−1) component associated with the gas in the disc of the galaxy and a broad (σ ≳ 200 km s−1) component produced by gas outflows. Emission-line ratio diagrams indicate that the gas in the disc is excited by the AGN radiation field, while the emission of the outflow includes additional contribution of shock excitation due to the interaction of the radio jet with the environment gas. Deviations from pure rotation, of up to 30 km s−1, are observed in the disc component and likely produced by a previous merger event. The broad component is blueshifted by ∼150–500 km s−1 relative to the systemic velocity of the galaxy in all locations. We construct radial profiles of the mass outflow rate and kinetic power of the ionized gas outflows, which have the maximum values at ∼1 kpc from the nucleus with peak values of $\dot{M}_{\rm out,\Delta R} = 0.5\pm 0.1$ M⊙ yr−1 and $\dot{K}_{\rm out,\Delta R} = (6.8\pm 1.1)\times 10^{41}$ erg s−1. The kinetic coupling efficiency of these outflows are in the range of 1–3 per cent, indicating that they could be powerful enough to affect the star formation in the host galaxy as predicted by theoretical simulations.
PubDate: Thu, 16 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• A Bayesian approach to modelling spectrometer data chromaticity corrected
using beam factors – I. Mathematical formalism

Pages: 3273 - 3297
Abstract: ABSTRACTAccurately accounting for spectral structure in spectrometer data induced by instrumental chromaticity on scales relevant for detection of the 21-cm signal is among the most significant challenges in global 21-cm signal analysis. In the publicly available Experiment to Detect the Global Epoch of Reionization Signature low-band data set, this complicating structure is suppressed using beam-factor-based chromaticity correction (BFCC), which works by dividing the data by a sky-map-weighted model of the spectral structure of the instrument beam. Several analyses of these data have employed models that start with the assumption that this correction is complete. However, while BFCC mitigates the impact of instrumental chromaticity on the data, given realistic assumptions regarding the spectral structure of the foregrounds, the correction is only partial. This complicates the interpretation of fits to the data with intrinsic sky models (models that assume no instrumental contribution to the spectral structure of the data). In this paper, we derive a BFCC data model from an analytical treatment of BFCC and demonstrate using simulated observations that, in contrast to using an intrinsic sky model for the data, the BFCC data model enables unbiased recovery of a simulated global 21-cm signal from beam-factor chromaticity-corrected data in the limit that the data are corrected with an error-free beam-factor model.
PubDate: Fri, 10 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Abell 1201: detection of an ultramassive black hole in a strong
gravitational lens

Pages: 3298 - 3322
Abstract: ABSTRACTSupermassive black holes (SMBHs) are a key catalyst of galaxy formation and evolution, leading to an observed correlation between SMBH mass MBH and host galaxy velocity dispersion σe. Outside the local Universe, measurements of MBH are usually only possible for SMBHs in an active state: limiting sample size and introducing selection biases. Gravitational lensing makes it possible to measure the mass of non-active SMBHs. We present models of the $z$ = 0.169 galaxy-scale strong lens Abell 1201. A cD galaxy in a galaxy cluster, it has sufficient ‘external shear’ that a magnified image of a $z$ = 0.451 background galaxy is projected just ∼1 kpc from the galaxy centre. Using multiband Hubble Space Telescope imaging and the lens modelling software PYAUTOLENS, we reconstruct the distribution of mass along this line of sight. Bayesian model comparison favours a point mass with MBH = 3.27 ± 2.12 × 1010 M⊙ (3σ confidence limit); an ultramassive black hole. One model gives a comparable Bayesian evidence without an SMBH; however, we argue this model is nonphysical given its base assumptions. This model still provides an upper limit of MBH ≤ 5.3 × 1010 M⊙, because an SMBH above this mass deforms the lensed image ∼1 kpc from Abell 1201’s centre. This builds on previous work using central images to place upper limits on MBH, but is the first to also place a lower limit and without a central image being observed. The success of this method suggests that surveys during the next decade could measure thousands more SMBH masses, and any redshift evolution of the MBH−σe relation. Results are available at https://github.com/Jammy2211/autolens_abell_1201.
PubDate: Wed, 29 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The ALMOND survey: molecular cloud properties and gas density tracers
across 25 nearby spiral galaxies with ALMA

Pages: 3348 - 3383
Abstract: ABSTRACTWe use new HCN(1–0) data from the ACA Large-sample Mapping Of Nearby galaxies in Dense gas (ALMOND) survey to trace the kpc-scale molecular gas density structure and CO(2–1) data from the Physics at High Angular resolution in Nearby GalaxieS–Atacama Large Millimeter/submillimeter Array (PHANGS–ALMA) to trace the bulk molecular gas across 25 nearby star-forming galaxies. At 2.1 kpc scale, we measure the density-sensitive HCN/CO line ratio and the star formation rate (SFR)/HCN ratio to trace the star formation efficiency in the denser molecular medium. At 150 pc scale, we measure structural and dynamical properties of the molecular gas via CO(2–1) line emission, which is linked to the lower resolution data using an intensity-weighted averaging method. We find positive correlations (negative) of HCN/CO (SFR/HCN) with the surface density, the velocity dispersion, and the internal turbulent pressure of the molecular gas. These observed correlations agree with expected trends from turbulent models of star formation, which consider a single free-fall time gravitational collapse. Our results show that the kpc-scale HCN/CO line ratio is a powerful tool to trace the 150 pc scale average density distribution of the molecular clouds. Lastly, we find systematic variations of the SFR/HCN ratio with cloud-scale molecular gas properties, which are incompatible with a universal star formation efficiency. Overall, these findings show that mean molecular gas density, molecular cloud properties, and star formation are closely linked in a coherent way, and observations of density-sensitive molecular gas tracers are a useful tool to analyse these variations, linking molecular gas physics to stellar output across galaxy discs.
PubDate: Wed, 08 Feb 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The VST ATLAS quasar survey I: Catalogue of photometrically selected
quasar candidates

Pages: 3384 - 3404
Abstract: ABSTRACTWe present the VST ATLAS Quasar Survey, consisting of ∼1229 000 quasar (QSO) candidates with 16 < g < 22.5 over ∼4700 deg2. The catalogue is based on VST ATLAS+NEOWISE imaging surveys and aims to reach a QSO sky density of 130 deg−2 for $z$ < 2.2 and ∼30 deg−2 for $z$ > 2.2. To guide our selection, we use X-ray/UV/optical/MIR data in the extended William Herschel Deep Field (WHDF) where we find a g < 22.5 broad-line QSO density of 269 ± 67 deg−2, roughly consistent with the expected ∼196 deg−2. We find that ∼25 per cent of our QSOs are morphologically classed as optically extended. Overall, we find that in these deep data, MIR, UV, and X-ray selections are ∼70–90 per cent complete while X-ray suffers less contamination than MIR and UV. MIR is however more sensitive than X-ray or UV to $z$ > 2.2 QSOs at g < 22.5 and the $S_X(0.5-10\, {\rm keV})\gt 1\times 10^{-14}$ ergs cm−2 s−1 limit of eROSITA. We adjust the selection criteria from our previous 2QDES pilot survey and prioritize VST ATLAS candidates that show both UV and MIR excess, also selecting candidates initially classified as extended. We test our selections using data from DESI (which will be released in DR1) and 2dF to estimate the efficiency and completeness, and we use ANNz2 to determine photometric redshifts. Applying over the ∼4700 deg2 ATLAS area gives us $\sim 917\,000\, z\lt 2.2$ QSO candidates of which 472 000 are likely to be $z$ < 2.2 QSOs, implying a sky density of ∼100 deg−2, which our WHDF analysis suggests will rise to at least 130 deg−2 when eROSITA X-ray candidates are included. At $z$ > 2.2, we find ∼310() 000 candidates, of which 169 000 are likely to be QSOs for a sky density of ∼36 deg−2.
PubDate: Mon, 20 Feb 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Revising the properties of low mass eclipsing binary stars using TESS
light curves

Pages: 3405 - 3420
Abstract: ABSTRACTPrecise measurements of stellar parameters are required in order to develop our theoretical understanding of stellar structure. These measurements enable errors and uncertainties to be quantified in theoretical models and constrain the physical interpretation of observed phenomena, such as the inflated radii of low-mass stars.We use newly-available TESS (Transiting Exoplanet Satellite Survey) light curves combined with published radial velocity measurements to improve the characterization of 12 low mass eclipsing binaries composed of an M dwarf accompanied by a brighter F/G star. We present and analyse ground-based simultaneous four-colour photometry for two targets. Our results include the first measurements of the fundamental properties of two of the systems. Light curve and radial velocity information were converted into the physical parameters of each component of the systems using an isochrone fitting method. We also derive the effective temperatures of the M dwarfs, almost tripling the number of such measurements.The results are discussed in the context of radius inflation. We find that exquisite precision in the age estimation of young objects is required to determine their inflation status. However, all but three of the objects are securely located among the main sequence, demonstrating radius inflation and the necessity to develop our understanding of the complex physical processes governing the evolution of low-mass stars. We investigated the hypothesis that luminosity is unaffected by the inflation problem but the findings were not conclusive.
PubDate: Mon, 20 Feb 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• On the gravitational lensing interpretation of three gravitational wave
detections in the mass gap by LIGO and Virgo

Pages: 3421 - 3430
Abstract: ABSTRACTWe search for gravitational wave (GW) events from LIGO-Virgo’s third run that may have been affected by gravitational lensing. Gravitational lensing delays the arrival of GWs, and alters their amplitude – thus biasing the inferred progenitor masses. This would provide a physically well-understood interpretation of GW detections in the ‘mass gap’ between neutron stars and black holes, as gravitationally lensed binary neutron star (BNS) mergers. We selected three GW detections in LIGO-Virgo’s third run for which the probability of at least one of the constituent compact objects being in the mass gap was reported as high with low latency – i.e. candidate lensed BNS mergers. Our observations of powerful strong lensing clusters located adjacent to the peak of their sky localization error maps reached a sensitivity $\rm AB\simeq 25.5$ in the z′ band with the GMOS instruments on the Gemini telescopes, and detected no candidate lensed optical counterparts. We combine recent kilonova light-curve models with recent predictions of the lensed BNS population and the properties of the objects that we followed up to show that realistic optical counterparts were detectable in our observations. Further detailed analysis of two of the candidates suggests that they are a plausible pair of images of the same low-mass binary black hole merger, lensed by a local galaxy or small group of galaxies. This further underlines that access to accurate mass information with low latency would improve the efficiency of candidate lensed BNS selection.
PubDate: Fri, 03 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Abundance analysis of a nitrogen-rich extreme-helium hot subdwarf from the
SALT survey

Pages: 3431 - 3440
Abstract: ABSTRACTWe have performed a detailed spectral analysis of the helium-rich hot subdwarf EC 20187−4939, using data obtained in the SALT survey of helium-rich hot subdwarfs. We have measured its effective temperature, surface gravity, and chemical abundances from the spectrum. Its radius has also been determined by fitting the spectral energy distribution using photometric data, from which a mass of 0.44$^{+0.32}_{-0.19}$ M⊙ has been inferred using the measurement of surface gravity. This star is particularly abundant in helium and nitrogen, whilst being both carbon and oxygen-weak. The surface abundances and mass have been found to be consistent with a helium white dwarf merger product. The abundance effects of alpha captures on nitrogen during the merger process and possible connections between EC 20187−4939, and other carbon-weak related objects are discussed.
PubDate: Tue, 07 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Estimating dynamical parameters of two interacting galaxies using deep
learning

Pages: 3441 - 3450
Abstract: ABSTRACTThe science behind Galaxy interaction and mergers has a fundamental role and gives us an insight into galaxy formation and its evolution. Fluctuating angular momentum is responsible for extraordinary events like polar rings, tidal tails, and ripples. Various parameters like the mass ratio of the interacting galaxy, orbital parameters, mass distribution, and morphologies are required to study different phenomena related to galaxy interactions. Convolutional neural networks (CNN) are widely used to predict image data. Thus, we used CNN as our approach to the problem. In this work, we will use data from state-of-the-art magnetohydrodynamic simulations of galaxy mergers from the GalMer database at different dynamical parameters using image snapshots of merging pairs of galaxies and feeding them to our Deep Learning model. The dynamical parameters we are aiming for would be spin, relative inclination (i), viewing angle (θ), and azimuthal angle (ϕ). We aim to download bulk data using the web scraping method. Here the model can predict the continuous and exact values of the dynamical parameters. We have achieved a 0.9986 R-squared value and a mean absolute error of 0.4348 on testing data. In the end, we used data from Sloan Digital Sky Survey to test our trained model on some real images.
PubDate: Tue, 07 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Gamma-ray flares and broad-band spectral study of PKS 0402-362

Pages: 3451 - 3474
Abstract: ABSTRACTWe study the long-term behaviour of the bright gamma-ray blazar PKS 0402-362. We collected approximately 13 yr of Fermi-LAT data between August 2008 to January 2021 and identified three bright γ-ray activity epochs. The second was found to be the brightest epoch ever seen in this source. We observed most of the γ-ray flare peaks to be asymmetric in profile suggesting a slow cooling time of particles or the varying Doppler factor as the main cause of these flares. The γ-ray spectrum is fitted with PL and LP spectral models, and in both cases, the spectral index is very steep. The γ-ray spectrum does not extend beyond 10 GeV energy suggesting the emission is produced within the BLR. The absence of time lags between optical-IR and γ-ray suggest one zone emission model. Using the above information, we have modelled the broad-band SED with a simple one-zone emission model using the publicly available code ‘GAMERA’. The particle distribution index is found to be the same as expected in diffusive shock acceleration suggesting it as the main mechanism of particle acceleration to very high energy up to 4–6 GeV. Throughout the various flux phases, we noticed that the optical emission is dominated by the thermal disc, suggesting it to be a good source to examine the disc-jet coupling. We postulate that the observed broad-band flares could be linked with perturbation produced in the disc, which propagates to the jet and interacts with the standing shock. However, a more detailed examination is required.
PubDate: Tue, 07 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Antenna source of radio-frequency emission in ion-proton pulsars

Pages: 3475 - 3479
Abstract: ABSTRACTThe growth of a longitudinal or quasi-longitudinal Langmuir mode in the outward-moving beam of ions and protons that forms the open sector of an ion-proton pulsar magnetosphere radiates as an analogue of an end-fed high-impedance horizontal straight-wire antenna an integral number of half-waves in length. The radiation has, broadly, the energy flux, linear polarization, and spectral index that are widely observed: also, the notch phenomenon seen in some integrated pulse profiles occurs naturally. The new field of pulsar observations below 100 MHz may lead to productive tests of the radio emission mechanism.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Surface structure of 45 Hercules: an otherwise unremarkable Ap star with a
surprisingly weak magnetic field

Pages: 3480 - 3499
Abstract: ABSTRACTThe origin of magnetic fields and their role in chemical spot formation on magnetic Ap stars is currently not understood. Here, we contribute to solving this problem with a detailed observational characterization of the surface structure of 45 Her, a weak-field Ap star. We find this object to be a long-period, single-lined spectroscopic binary and determine the binary orbit as well as fundamental and atmospheric parameters of the primary. We study magnetic field topology and chemical spot distribution of 45 Her with the help of the Zeeman Doppler imaging technique. Magnetic mapping reveals the stellar surface field to have a distorted dipolar topology with a surface-averaged field strength of 77 G and a dipolar component strength of 119 G – confirming it as one of the weakest well-characterized Ap-star fields known. Despite its feeble magnetic field, 45 Her shows surface chemical inhomogeneities with abundance contrasts of up to 6 dex. Of the four chemical elements studied, O concentrates at the magnetic equator, whereas Ti, Cr, and Fe avoid this region. Apart from this trend, the positions of Fe-peak element spots show no apparent correlation with the magnetic field geometry. No signs of surface differential rotation or temporal evolution of chemical spots on the time-scale of several years were detected. Our findings demonstrate that chemical spot formation does not require strong magnetic fields to proceed and that both the stellar structure and the global field itself remain stable for sub-100 G field strengths contrary to theoretical predictions.
PubDate: Thu, 09 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Exciting spiral arms in protoplanetary discs from flybys

Pages: 3500 - 3516
Abstract: ABSTRACTSpiral arms are observed in numerous protoplanetary discs. These spiral arms can be excited by companions, either on bound or unbound orbits. We simulate a scenario where an unbound perturber, i.e. a flyby, excites spiral arms during a periastron passage. We run three-dimensional hydrodynamical simulations of a parabolic flyby encountering a gaseous protoplanetary disc. The perturber mass ranges from $10\, \rm M_J$ to $1\, \rm {\rm M}_{\odot }$. The perturber excites a two-armed spiral structure, with a more prominent spiral feature for higher mass perturbers. The two arms evolve over time, eventually winding up, consistent with previous works. We focus on analysing the pattern speed and pitch angle of these spirals during the whole process. The initial pattern speed of the two arms are close to the angular velocity of the perturber at periastron, and then it decreases over time. The pitch angle also decreases over time as the spiral winds up. The spirals disappear after several local orbital times. An inclined prograde orbit flyby induces similar disc substructures as a coplanar flyby. A solar-mass flyby event causes increased eccentricity growth in the protoplanetary disc, leading to an eccentric disc structure which dampens over time. The spirals’ morphology and the disc eccentricity can be used to search for potential unbound stars or planets around discs where a flyby is suspected. Future disc observations at high resolution and dedicated surveys will help to constrain the frequency of such stellar encounters in nearby star-forming regions.
PubDate: Mon, 13 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• TESS shines light on the origin of the ambiguous nuclear transient
ASASSN-18el

Pages: 3517 - 3526
Abstract: ABSTRACTWe analyse high-cadence data from the Transiting Exoplanet Survey Satellite (TESS) of the ambiguous nuclear transient (ANT) ASASSN-18el. The optical changing-look phenomenon in ASASSN-18el has been argued to be due to either a drastic change in the accretion rate of the existing active galactic nucleus (AGN) or the result of a tidal disruption event (TDE). Throughout the TESS observations, short-time-scale stochastic variability is seen, consistent with an AGN. We are able to fit the TESS light curve with a damped-random-walk (DRW) model and recover a rest-frame variability amplitude of $\hat{\sigma } = 0.93 \pm 0.02$ mJy and a rest-frame time-scale of $\tau _{DRW} = 20^{+15}_{-6}$ d. We find that the estimated τDRW for ASASSN-18el is broadly consistent with an apparent relationship between the DRW time-scale and central supermassive black hole mass. The large-amplitude stochastic variability of ASASSN-18el, particularly during late stages of the flare, suggests that the origin of this ANT is likely due to extreme AGN activity rather than a TDE.
PubDate: Thu, 16 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Andromeda XXV – a dwarf galaxy with a low central dark matter
density

Pages: 3527 - 3539
Abstract: ABSTRACTAndromeda (And) XXV has previously been reported as a dwarf spheroidal galaxy (dSph) with little-to-no dark matter. However, the uncertainties on this result were significant. In this study, we nearly double the number of member stars and re-derive the kinematics and mass of And XXV. We find that And XXV has a systemic velocity of νr = −107.7 ± 1.0 kms−1 and a velocity dispersion of $\sigma _{\rm \nu }=3.7^{+1.2}_{-1.1}$ kms−1. With this updated velocity dispersion and a new literature measurement of the radial surface brightness profile, we derive a mass contained within the half-light radius of $M(r\lt r_{\rm h})=4.7^{+3.0}_{-2.9}\times 10^6$ M⊙. This mass corresponds to a mass-to-light ratio of $\text{[M/L]}_{\rm r_{h}}=25^{+17}_{-16}$ M⊙/L⊙, demonstrating that And XXV is most-likely dark matter dominated. We also measure the metallicity of And XXV to be $\rm [Fe/H]=-1.9\pm 0.1$ dex, which is in agreement with previous results. Finally, we extend the analysis of And XXV to include mass modelling using GravSphere. We find that And XXV has a low central dark matter density, ρDM(150 pc) = $2.3^{+1.4}_{-1.1}\times 10^7$ M⊙ kpc−3, which makes And XXV a clear outlier when compared to other local group dSphs of the similar stellar mass. In a companion paper, we will explore whether some combination of dark matter cusp-core transformations and/or tides can explain And XXV’s low density.
PubDate: Tue, 14 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The LMC impact on the kinematics of the Milky Way satellites: clues from
the running solar apex

Pages: 3540 - 3552
Abstract: ABSTRACTDwarf galaxies provide a unique opportunity for studying the evolution of the Milky Way (MW) and the Local Group as a whole. Analysing the running solar apex based on the kinematics of the MW satellites, we discovered an unexpected behaviour of the dipole term of the radial velocity distribution as a function of the Galactocentric distance. The nearby satellites (<100 kpc) have a bulk motion with an amplitude of 140–230 km s−1, while the more distant ones show an isotropic distribution of the radial velocities. Such strong solar apex variations cannot be explained by the net rotation of the satellites, as it would require an enormously high rotation rate (≈970 km s−1). If we exclude the Large and Magellanic Clouds (LMC) and its most closely related members from our sample, this does not suppress the bulk motion of the nearby satellites strongly enough. Nevertheless, we have demonstrated that the observed peculiar kinematics of the MW satellites can be explained by a perturbation caused by the first infall of the LMC. First, we ‘undone’ the effect of the perturbation by integrating the orbits of the MW satellites backwards (forwards) with (without) massive LMC. It appears that the present-day peculiar enhancement of the solar apex in the inner halo is diminished the most in the case of 2 × 1011 M⊙ LMC. Next, in self-consistent high-resolution N-body simulations of the MW–LMC interaction, we found that the solar apex shows the observed behaviour only for the halo particles with substantial angular momentum, comparable to that of the MW satellites.
PubDate: Wed, 15 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Formation of supermassive stars in the first star clusters

Pages: 3553 - 3569
Abstract: ABSTRACTThe formation of supermassive stars is believed to be an essential intermediate step for the formation of the massive black hole seeds that become the supermassive black holes powering the quasars observed in the early Universe. Numerical simulations have shown that supermassive stars can form in atomic-cooling haloes when protostars reach accretion rates higher than ∼10−2 M⊙ yr−1 and fragmentation is suppressed on pc scales. It is, however, still uncertain if a supermassive star still emerges when fragmentation occurs at smaller scales and a cluster of stars is formed instead. In this work, we explore the problem of massive object formation due to the interplay of collisions and accretion in star clusters at low metallicity. We model a small embedded cluster of accreting protostars following subparsec scale fragmentation during the collapse of a primordial gas cloud, and follow its evolution by performing N-body plus hydrodynamical simulations. Our results show that supermassive stars with 103 and 104 M⊙ are always formed due to the interplay of collisions and accretion, and in some cases these objects are part of a binary system. The resulting supermassive star is surrounded by tens of smaller stars with typical masses in the range 1–100 M⊙.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Fast transitions of X-ray variability in the black hole transient GX
339−4: comparison with MAXI J1820+070 and MAXI J1348−630

Pages: 3570 - 3584
Abstract: ABSTRACTFast transitions between different types of power density spectra (PDS) happening over time-scales of several tens of seconds are rare phenomena in black hole X-ray binaries. In this paper, we report a broad-band spectral-timing analysis of the fast transitions observed in the 2021 outburst of GX 339−4 using NICER and Insight-HXMT observations. We observe transitions between band-limited noise-dominated PDS and type-B quasi-periodic oscillations (QPOs), and their rapid appearance or disappearance. We also make a detailed comparison between the fast transitions in GX 339−4 with those seen in MAXI J1820+070 and MAXI J1348−630. By comparing the spectra of the periods with and without type-B QPOs, we find that the spectral ratios above 10 keV are nearly constant or slightly decreasing, and the values are different between sources. Below 10 keV, the flux change of the Comptonization component is inversely proportional to the flux change of the thermal component, suggesting that the appearance of type-B QPOs is associated with a redistribution of the accretion power between the disc and the Comptonizing emission region. The spectral ratios between the periods with type-B QPO and those with broad-band noise are significantly different from that with type-B QPO and without type-B QPO, where the ratios (type-B QPO/broad-band noise) show a maximum at around 4 keV and then decrease gradually towards high energies. Finally, we discuss the possible change of the geometry of the inner accretion flow and/or jet during the transitions.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Solar wind interaction with Mars: electric field morphology and source
terms

Pages: 3597 - 3607
Abstract: ABSTRACTThe correlation between space environment conditions and the properties of escaping ions is a central topic of Mars research. Although empirical correlations have been visible in the data, a physics-based interpretation, rather than statistics-based pictures, has not been established yet. As a first effort, we investigate the electric field, the direct contributor to ion acceleration, in the Mars plasma environment from a hybrid plasma model (particle ions and fluid electrons). We use Amitis, a hybrid model combined with an observation-based ionospheric model, to simulate the Mars–solar wind interaction under nominal solar wind plasma conditions for perpendicular and Parker spiral directions of the interplanetary magnetic field (IMF). The simulations show following results: (1) the electric field morphology is structured by the IMF direction and the different plasma domains in the solar wind–Mars interaction; (2) asymmetry of the electric field between the hemispheres where the convective electric field points inward and outward, respectively, due to the mass loading and asymmetric draping of the magnetic field lines; (3) the motional electric field dominates in most regions, especially in the dayside magnetosheath; and (4) the Hall term is an order of magnitude weaker and significant in the magnetotail and plasma boundaries for a perpendicular IMF case. The Hall term is relatively stronger for the Parker spiral case. (5) The ambipolar electric field, in principle, agrees with Mars Atmosphere and Volatile Evolution measurements in the magnetosheath.
PubDate: Wed, 25 Jan 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• A catalogue of unusually long thermonuclear bursts on neutron stars

Pages: 3608 - 3624
Abstract: ABSTRACTRare, energetic (long) thermonuclear (Type I) X-ray bursts are classified either as intermediate-duration or ‘supern’ bursts, based on their duration. Intermediate-duration bursts lasting a few to tens of minutes are thought to arise from the thermonuclear runaway of a relatively thick (≈1010 g cm−2) helium layer, while superbursts lasting hours are attributed to the detonation of an underlying carbon layer. We present a catalogue of 84 long thermonuclear bursts from 40 low-mass X-ray binaries, and defined from a new set of criteria distinguishing them from the more frequent short bursts. The three criteria are: (1) a total energy release longer than 1040 erg, (2) a photospheric radius expansion phase longer than 10 s, and (3) a burst time-scale longer than 70 s. This work is based on a comprehensive systematic analysis of 70 bursts found with INTEGRAL, RXTE, Swift, BeppoSAX, MAXI, and NICER, as well as 14 long bursts from the literature that were detected with earlier generations of X-ray instruments. For each burst, we measure its peak flux and fluence, which eventually allows us to confirm the distinction between intermediate-duration bursts and superbursts. Additionally, we list 18 bursts that only partially meet the above inclusion criteria, possibly bridging the gap between normal and intermediate-duration bursts. With this catalogue, we significantly increase the number of long-duration bursts included in the MINBAR and thereby provide a substantial sample of these rare X-ray bursts for further study.
PubDate: Thu, 02 Feb 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Coherent and incoherent structures in fuzzy dark matter haloes

Pages: 3625 - 3647
Abstract: ABSTRACTWe show that fuzzy dark matter haloes exhibit spatial differentiation in the coherence of the field configuration, ranging from completely coherent in the central solitonic core to incoherent outside it, with a significant drop of the dimensionless phase-space density with increasing radius. The core is a pure condensate, overlapping perfectly with the Penrose-Onsager mode corresponding to the largest eigenvalue of the one-particle density matrix. The virialized outer halo exhibits no clear coherence as a whole upon radial and temporal averaging but can be described as a collection of local, short-lived quasi-condensate lumps, exhibiting suppressed fluctuations, which can be identified with the structures commonly referred to as granules. These localized regions are separated by vortices that form a dynamical web, inhibiting phase coherence across the entire halo. We further examine the core oscillations, finding that they are accurately described by two time-dependent parameters characterizing the size of the core, rc(t), and a crossover region, rt(t). For the haloes in our merger simulations, this feature is reflected in the (anti-)correlated oscillation of the peak value of the density power-spectrum. The halo’s turbulent vortex tangle appears to reach a quasi-equilibrium state over probed time-scales, with the incompressible component of the kinetic energy exhibiting a characteristic k−3 tail in its spectrum, indicative of a ρ ∼ r2 density profile around the quantum vortex cores. Comparison of the peak wavenumbers in the corresponding power-spectra shows the inter-vortex spacing and the granule length scale in the outer halo to be very similar and slightly above the core size.
PubDate: Fri, 24 Feb 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Cosmological Fisher forecasts for next-generation spectroscopic surveys

Pages: 3648 - 3662
Abstract: ABSTRACTNext-generation spectroscopic surveys such as the MegaMapper, MUltiplexed Survey Telescope (MUST), MaunaKea Spectroscopic Explorer (MSE), and WideField Spectroscopic Telescope (WST) are foreseen to increase the number of galaxy/quasar redshifts by an order of magnitude, with hundred millions of spectra that will be measured at z > 2. We perform a Fisher matrix analysis for these surveys on the baryonic acoustic oscillation (BAO), the redshift-space distortion (RSD) measurement, the non-Gaussianity (NG) amplitude fNL, and the total neutrino mass Mν. For BAO and RSD parameters, these surveys may achieve precision at sub-per cent level (<0.5 per cent), representing an improvement of factor 10 w.r.t. the latest data base. For NG, these surveys may reach an accuracy of σ(fNL) ∼ 1. They can also put a tight constraint on Mν with $\sigma (M_\nu) \sim 0.02\, \rm eV$ if we do joint analysis with Planck and even $0.01\, \rm eV$ if combined with other data. In addition, we introduce a general survey model to derive the cosmic volume and number density of tracers, given instrumental facilities and survey strategy. Using our Fisher formalism, we can explore (continuously) a wide range of survey observational parameters and propose different survey strategies that optimize the cosmological constraints. Fixing the fibre number and survey duration, we show that the best strategy for fNL and Mν measurement is to observe large volumes, despite the noise increase. However, the strategy differs for the apparent magnitude limit. Finally, we prove that increasing the fibre number improves Mν measurement but not significantly fNL.
PubDate: Thu, 23 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The occurrence rate of giant planets orbiting low-mass stars with TESS

Pages: 3663 - 3681
Abstract: ABSTRACTWe present a systematic search for transiting giant planets ($0.6 \mbox{$R_{\rm J}$}\le \mbox{$R_{\rm P}$}\le 2.0 \mbox{$R_{\rm J}$}$) orbiting nearby low-mass stars ($\mbox{$M_{*}$}\le 0.71 \mbox{${\rm M}_{\odot }$}$). The formation of giant planets around low-mass stars is predicted to be rare by the core-accretion planet formation theory. We search 91 306 low-mass stars in the TESS 30 min cadence photometry detecting fifteen giant planet candidates, including seven new planet candidates which were not known planets or identified as TOIs prior to our search. Our candidates present an exciting opportunity to improve our knowledge of the giant planet population around the lowest mass stars. We perform planet injection-recovery simulations and find that our pipeline has a high detection efficiency across the majority of our targeted parameter space. We measure the occurrence rates of giant planets with host stars in different stellar mass ranges spanning our full sample. We find occurrence rates of 0.137 ± 0.097  per cent (0.088–0.26 M⊙), 0.108 ± 0.083 per cent (0.26–0.42 M⊙), and 0.29 ± 0.15 per cent (0.42–0.71 M⊙). For our full sample (0.088–0.71 M⊙), we find a giant planet occurrence rate of 0.194 ± 0.072 per cent. We have measured for the first time the occurrence rate for giant planets orbiting stars with $\mbox{$M_{*}$}\le 0.4\, \mbox{${\rm M}_{\odot }$}$ and we demonstrate this occurrence rate to be non-zero. This result contradicts currently accepted planet formation models and we discuss some possibilities for how these planets could have formed.
PubDate: Fri, 03 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Characterising SMSS J2157–3602, the most luminous known quasar, with
accretion disc models

Pages: 3682 - 3698
Abstract: ABSTRACTWe develop an accretion disc (AD)-fitting method, utilizing thin and slim disc models and Bayesian inference with the Markov-Chain Monte Carlo approach, testing it on the most luminous known quasar, SMSS J215728.21-360215.1, at redshift z = 4.692. With a spectral energy distribution constructed from near-infrared spectra and broad-band photometry, the AD models find a black hole mass of $\log (M_{\rm {AD}}/{\rm M}_{\odot }) = 10.31^{+0.17}_{-0.14}$ with an anisotropy-corrected bolometric luminosity of $\log {(L_{\rm {bol}}/\rm {erg\, s^{-1}})} = 47.87 \pm 0.10$ and derive an Eddington ratio of $0.29^{+0.11}_{-0.10}$ as well as a radiative efficiency of $0.09^{+0.05}_{-0.03}$. Using the near-infrared spectra, we estimate the single-epoch virial black hole mass estimate to be log (MSE/M⊙) = 10.33 ± 0.08, with a monochromatic luminosity at 3000 Å of $\log {(L(\rm {3000{\AA}})/\rm {erg\, s^{-1}})} = 47.66 \pm 0.01$. As an independent approach, AD fitting has the potential to complement the single-epoch virial mass method in obtaining stronger constraints on properties of massive quasar black holes across a wide range of redshifts.
PubDate: Thu, 02 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• A search for chemical anomalies of seven A-type stars

Pages: 3699 - 3707
Abstract: ABSTRACTWe present a chemical abundance analysis of seven A-type stars with no detailed chemical abundance measurements in the literature. High-resolution spectra of the targets – HD 2924, HD 4321, HD 26553, HD 125658, HD 137928, HD 154713, and HD 159834 – were obtained using the Coudé Echelle Spectrograph at the TÜBİTAK National Observatory. We determined the atmospheric abundances of the samples and measured the elemental abundances of C, N, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu, and Gd. The masses of the stars were estimated based on their evolutionary tracks, and their ages were calculated using isochrones. We also calculated the radii of the stars. The abundance patterns of HD 4321, HD 125658, and HD 154713 were found to be in agreement with those of classical Am stars, with underabundant Ca and Sc, overabundant heavier elements, and moderate overabundance of iron-peak elements. We found that HD 137928 and HD 159834 have abundance characteristics similar to marginal Am-type stars. The elemental distributions of HD 2924 and HD 26553 are consistent with the pattern of normal A-type stars. The iron, nickel, and zinc abundances of HD 125658 and HD 137928 are significantly higher than those of other Am stars. These values suggest that they are among the most metal-rich Am stars.
PubDate: Fri, 03 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Spiral arms are metal freeways: azimuthal gas-phase metallicity variations
in flocculent discs in the FIRE-2 cosmological zoom-in simulations

Pages: 3708 - 3726
Abstract: ABSTRACTWe examine the azimuthal variations in gas-phase metallicity profiles in simulated Milky Way-mass disc galaxies from the Feedback in Realistic Environments (FIRE-2) cosmological zoom-in simulation suite, which includes a sub-grid turbulent metal mixing model. We produce spatially resolved maps of the discs at z ≈ 0 with pixel sizes ranging from 250 to 750 pc, analogous to modern integral field unit galaxy surveys, mapping the gas-phase metallicities in both the cold and dense gas and the ionized gas correlated with H ii regions. We report that the spiral arms alternate in a pattern of metal rich and metal poor relative to the median metallicity of the order of ≲0.1 dex, appearing generally in this sample of flocculent spirals. The pattern persists even in a simulation with different strengths of metal mixing, indicating that the pattern emerges from physics above the sub-grid scale. Local enrichment does not appear to be the dominant source of the azimuthal metallicity variations at z ≈ 0: there is no correlation with local star formation on these spatial scales. Rather, the arms are moving radially inwards and outwards relative to each other, carrying their local metallicity gradients with them radially before mixing into the larger-scale interstellar medium. We propose that the arms act as freeways channeling relatively metal poor gas radially inwards, and relatively enriched gas radially outwards.
PubDate: Mon, 06 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The GALAH survey: new diffuse interstellar bands found in residuals of
872 000 stellar spectra

Pages: 3727 - 3748
Abstract: ABSTRACTWe use more than 872 000 mid- to high-resolution (R ∼ 20 000) spectra of stars from the GALactic Archaeology with HERMES (GALAH) survey to discern the spectra of diffuse interstellar bands (DIBs). We use four windows with the wavelength ranges 4718–4903, 5649–5873, 6481–6739, and 7590–7890 Å, giving a total coverage of 967 Å. We produce ∼400 000 spectra of interstellar medium (ISM) absorption features and correct them for radial velocities of the DIB clouds. Ultimately, we combine the 33 115 best ISM spectra into six reddening bins with a range of 0.1 < E(B − V) < 0.7 mag. A total of 183 absorption features in these spectra qualify as DIBs, and their fitted model parameters are summarized in a detailed catalogue. From these, 64 are not reported in the literature, of which 17 are certain, 14 are probable and 33 are possible. We find that the broad DIBs can be fitted with a multitude of narrower DIBs. Finally, we create a synthetic DIB spectrum at unit reddening. This should allow us to narrow down the possible carriers of DIBs, to explore the composition of the ISM, and ultimately to model dust and star formation better as well as to correct Galactic and extragalactic observations. The majority of certain DIBs show a significant excess of equivalent width when compared with reddening. We explain this with observed lines of sight penetrating more uniform DIB clouds compared with clumpy dust clouds.
PubDate: Sat, 25 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The TESS Triple-9 Catalog II: a new set of 999 uniformly vetted exoplanet
candidates

Pages: 3749 - 3764
Abstract: ABSTRACTThe Transiting Exoplanet Survey Satellite (TESS) mission is providing the scientific community with millions of light curves of stars spread across the whole sky. Since 2018, the telescope has detected thousands of planet candidates that need to be meticulously scrutinized before being considered amenable targets for follow-up programs. We present the second catalog of the Planet Patrol citizen science project containing 999 uniformly vetted exoplanet candidates within the TESS ExoFOP archive. The catalog was produced by fully exploiting the power of the Citizen Science Planet Patrol project. We vetted TESS Objects of Interest (TOIs) based on the results of Discovery And Vetting of Exoplanets (dave) pipeline. We also implemented the automatic disposition generator, a custom procedure aimed at generating the final classification for each TOI that was vetted by at least three vetters. The majority of the candidates in our catalog, 752 TOIs, passed the vetting process and were labelled as planet candidates. We ruled out 142 candidates as false positives and flagged 105 as potential false positives. Our final dispositions and comments for all the planet candidates are provided as a publicly available supplementary table.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Census of gaseous satellites around local spiral galaxies

Pages: 3765 - 3783
Abstract: ABSTRACTWe present a search for gas-containing dwarf galaxies as satellite systems around nearby spiral galaxies using 21 cm neutral hydrogen (H i) data from the Arecibo Legacy Fast ALFA (ALFALFA) Survey. We have identified 15 spiral ‘primary’ galaxies in a local volume of 10 Mpc with a range of total masses, and have found 19 gas-containing dwarf satellite candidates within the primaries’ virial volumes (R200) and 46 candidates within 2R200. Our sensitivity using ALFALFA data converts to MH i ≈ 7.4 × 106 M⊙ at 10 Mpc, which includes 13 of the 26 gaseous dwarf galaxies in the Local Group, and the H i properties of our sample are overall similar to these 13. We found 0–3 gaseous satellites per host galaxy within R200 and 0–5 within 2R200, which agrees with the low numbers present for the Milky Way and M31. There is also agreement with the star-forming satellite numbers per host in the deep optical surveys SAGA and ELVES, and the Auriga cosmological simulations. When scaled to R200, the optical surveys do not show a trend of increasing quenched fraction with host mass; there is a slight increase in the total number of gaseous satellites with host mass for our sample. The low numbers of gaseous/star-forming satellites around spiral hosts are consistent with the idea that a universal and effective satellite quenching mechanism, such as ram pressure stripping by the host halo, is likely at play.
PubDate: Tue, 07 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Observations of two superfast rotator NEAs: 2021 NY1 and 2022 AB

Pages: 3784 - 3792
Abstract: ABSTRACTIn the framework of the visible NEAs observations survey (ViNOS) that uses several telescopes at the Canary Islands observatories since 2018, we observed two superfast rotator NEAs, 2021 NY1 and 2022 AB. We obtained photometry and spectrophotometry of both targets and visible spectroscopy of 2022 AB. Light curves of 2021 NY1 obtained in four different nights between 2021 September 30 and 2021 October 16 return a rotation period P = 13.3449 ± 0.0013 minutes and a light curve amplitude A = 1.00 mag. We found that 2021 NY1 is a very elongated superfast rotator with an axis ratio a/b ≥ 3.6. We also report colours (g − r) = 0.664 ± 0.013, (r − i) = 0.186 ± 0.013, and (i − zs) = −0.117 ± 0.012 mag. These are compatible with an S-type asteroid. The light curves of 2022 AB obtained on 2021 January 5 and 2021 January 8 show a rotation period P = 3.0304 ± 0.0008 min, with amplitudes A = 0.52 and A = 0.54 mag. 2022 AB is also an elongated object with axis ratio a/b ≥ 1.6. The obtained colours are (g − r) = 0.400 ± 0.017, (r − i) = 0.133 ± 0.017, and (i − zs) = 0.093 ± 0.016. These colours are similar to those of the X-types, but with an unusually high (g − r) value. Spectra obtained on 2022 January 12 and 2022 January 14 are consistent with the reported colours. The spectral upturn over the 0.4 - 0.6 $\mu \mathrm{m}$ region of 2022 AB does not fit with any known asteroid taxonomical class or meteorite spectrum, confirming its unusual surface properties.
PubDate: Thu, 09 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Detecting and characterizing pulsar haloes with the Cherenkov telescope
array

Pages: 3793 - 3809
Abstract: ABSTRACTThe recently identified source class of pulsar haloes may be numerous and bright enough in the TeV energy range to constitute a large fraction of the sources that will be observed with the Cherenkov Telescope Array (CTA). In this work, we quantify the prospects for detecting and characterizing pulsar haloes in observations of the projected Galactic Plane Survey (GPS), using a simple phenomenological diffusion model for individual pulsar haloes and their population in the Milky Way. Our ability to uncover pulsar haloes and constrain their main physical parameters in the CTA GPS is assessed in the framework of a full spatial-spectral likelihood analysis of simulated survey observations, using the most recent estimates for the instrument response function and prototypes for the science tools. For a model setup representative of the halo around Geminga, we find that about three hundred objects could give rise to detectable emission in the GPS survey. Yet, only a third of them could be identified through their energy-dependent morphology, and only one-tenth of them would allow the derivation of strong constraints on key physical parameters like the magnitude or extent of suppressed diffusion around the pulsar. We also provide a list of known pulsars that could be hosting a detectable (Geminga-like) halo in the GPS and assess the robustness of our findings against several systematic uncertainties.
PubDate: Thu, 09 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Multiple flares in the changing-look AGN NGC 5273

Pages: 3810 - 3829
Abstract: ABSTRACTNGC 5273 is a known optical and X-ray variable AGN. We analyse new and archival IR, optical, UV, and X-ray data in order to characterize its long-term variability from 2000–2022. At least one optical changing-look event occurred between 2011 and 2014 when the AGN changed from a Type 1.8/1.9 Seyfert to a Type 1. It then faded considerably at all wavelengths, followed by a dramatic but slow increase in UV/optical brightness between 2021 and 2022. Near-IR (NIR) spectra in 2022 show prominent broad Paschen lines that are absent in an archival spectrum from 2010, making NGC 5273 one of the few AGNs to be observed changing-look in the NIR. We propose that NGC 5273 underwent multiple changing-look events between 2000 and 2022 – starting as a Type 1.8/1.9, NGC 5273 changes-look to a Type 1 temporarily in 2002 and again in 2014, reverting back to a Type 1.8/1.9 by 2005 and 2017, respectively. In 2022, it is again a Type 1 Seyfert. We characterize the changing-look events and their connection to the dynamic accretion and radiative processes in NGC 5273 and propose that the variable luminosity (and thus, Eddington ratio) of the source is changing how the broad-line region (BLR) reprocesses the continuum emission.
PubDate: Sat, 11 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Relative alignment between magnetic fields and molecular gas structure in
molecular clouds

Pages: 3830 - 3846
Abstract: ABSTRACTWe compare the structure of synthetic dust polarization with synthetic molecular line emission from radiative transfer calculations using a three-dimensional, turbulent collapsing-cloud magnetohydrodynamics simulation. The histogram of relative orientation (HRO) technique and the projected Rayleigh statistic (PRS) are considered. In our trans-Alfvénic (more strongly magnetized) simulation, there is a transition to perpendicular alignment at densities above ∼4 × 103 cm−3. This transition is recovered in most of our synthetic observations of optically thin molecular tracers; however, for 12CO it does not occur and the PRS remains in parallel alignment across the whole observer space. We calculate the physical depth of the optical depth τ = 1 surface and find that for 12CO it is largely located in front of the cloud mid-plane, suggesting that 12CO is too optically thick and instead mainly probes low-volume density gas. In our super-Alfvénic simulation, the magnetic field becomes significantly more tangled, and all observed tracers tend towards no preference for perpendicular or parallel alignment. An observable difference in alignment between optically thin and optically thick tracers may indicate the presence of a dynamically important magnetic field, though there is some degeneracy with viewing angle. We convolve our data with a Gaussian beam and compare it with HRO results of the Vela C molecular cloud. We find good agreement between these results and our sub-Alfvénic simulations when viewed with the magnetic field in the plane of the sky (especially when sensitivity limitations are considered), though the observations are also consistent with an intermediately inclined magnetic field.
PubDate: Tue, 14 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The properties of RR Lyrae variable stars in the isolated Local Group
dwarf galaxy WLM

Pages: 3847 - 3860
Abstract: ABSTRACTWe present an analysis of 50 F475W (≈B filter) and F814W (≈I filter) archival images taken with the Hubble Space Telescope (HST)/Advanced Camera for Surveys of one field in the isolated Local Group dwarf galaxy Wolf–Lundmark–Melotte (WLM). From point spread function fitting photometry of these images, we construct a colour–magnitude diagram and identify and characterize 90 RR Lyrae variables (76 ab-type and 14 c-type) determining their mean magnitudes, colours, periods, and amplitudes in the HST passbands. We have also uncovered 79 Cepheid-type variables, but because of the short time window of our observations (1.85 d), we are not confident in their period determinations. The mean period of the ab-type RR Lyraes is found to be 〈Pab〉 = 0.609 ± 0.058 (ran) corresponding to a mean metallicity of 〈[Fe/H]〉 = −1.74 ± 0.02 (ran) on the Carretta et al. scale. We also present a re-analysis of the Hodge et al. colour–magnitude diagram of the WLM globular cluster and conclude that it is much more metal-poor than Hodge et al. quote. Based on a comparison of the WLM RR Lyraes with those in the other seven ‘isolated’ dwarf galaxies of the Local Group (i.e. Leo A, LGS 3, Cetus, IC 1613, Aquarius, Tucana, and Phoenix), we conclude that there was one unique epoch of early star formation common to all of these isolated dwarfs.
PubDate: Thu, 16 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Identification of tidal features in deep optical galaxy images with
convolutional neural networks

Pages: 3861 - 3872
Abstract: ABSTRACTInteractions between galaxies leave distinguishable imprints in the form of tidal features, which hold important clues about their mass assembly. Unfortunately, these structures are difficult to detect because they are low surface brightness features, so deep observations are needed. Upcoming surveys promise several orders of magnitude increase in depth and sky coverage, for which automated methods for tidal feature detection will become mandatory. We test the ability of a convolutional neural network to reproduce human visual classifications for tidal detections. We use as training ∼6000 simulated images classified by professional astronomers. The mock Hyper Suprime Cam Subaru (HSC) images include variations with redshift, projection angle, and surface brightness (μlim = 26–35 mag arcsec−2). We obtain satisfactory results with accuracy, precision, and recall values of Acc = 0.84, P = 0.72, and R  = 0.85 for the test sample. While the accuracy and precision values are roughly constant for all surface brightness, the recall (completeness) is significantly affected by image depth. The recovery rate shows strong dependence on the type of tidal features: we recover all the images showing shell features and 87 per cent of the tidal streams; these fractions are below 75 per cent for mergers, tidal tails, and bridges. When applied to real HSC images, the performance of the model worsens significantly. We speculate that this is due to the lack of realism of the simulations, and take it as a warning on applying deep learning models to different data domains without prior testing on the actual data.
PubDate: Wed, 22 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Direct analysis of the broad-line SN 2019ein: connection with the
core-normal SN 2011fe

Pages: 3873 - 3881
Abstract: ABSTRACTType Ia supernovae (SNe Ia) are important cosmological probes and contributors to galactic nucleosynthesis, particularly of the iron group elements. To improve both their reliability as cosmological probes and to understand galactic chemical evolution, it is vital to understand the binary progenitor system and explosion mechanism. The classification of SNe Ia into Branch groups has led to some understanding of the similarities and differences among the varieties of observed SNe Ia. Branch groups are defined by the pseudo-equivalent widths of the two prominent Si ii lines, leading to four distinct groups: core-normal (CN), shallow-silicon, cool, and broad-line (BL). However, partly due to small sample size, little work has been done on the BL group. We perform direct spectral analysis on the pre-maximum spectra of the BL SN 2019ein, comparing and contrasting to the CN SN 2011fe. Both SN 2019ein and SN 2011fe were first observed spectroscopically within 2 d of discovery, allowing us to follow the spectroscopic evolution of both SNe in detail. We find that the optical depths of the primary features of both the CN and BL SNe are very similar, except that there is a Doppler shift between them. We further examine the BL group and show that for nine objects with pre-maximum spectra in the range (−6)–(−2) d with respect to B-maximum all the emission peaks of the Si ii λ6355 line of BL are blueshifted pre-maximum, suggesting a possible classification criterion.
PubDate: Thu, 16 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• A reconnection-driven magnetic flux cancellation and a quiet Sun Ellerman
bomb

Pages: 3882 - 3897
Abstract: ABSTRACTThe focus of this investigation is to quantify the conversion of magnetic to thermal energy initiated by a quiet Sun cancellation event and to explore the resulting dynamics from the interaction of the opposite-polarity magnetic features. We used imaging spectroscopy in the Hα line, along with spectropolarimetry in the Fe i 6173 Å and Ca ii 8542 Å lines from the Swedish Solar Telescope (SST) to study a reconnection-related cancellation and the appearance of a quiet Sun Ellerman bomb (QSEB). We observed, for the first time, QSEB signature in both the wings and core of the Fe i 6173 Å line. We also found that, at times, the Fe i line-core intensity reaches higher values than the quiet Sun continuum intensity. From FIRTEZ-dz inversions of the Stokes profiles in Fe i and Ca ii lines, we found enhanced temperature, with respect to the quiet Sun values, at the photospheric (log τc  = −1.5; ∼1000 K) and lower chromospheric heights (log τc  = −4.5; ∼360 K). From the calculation of total magnetic energy and thermal energy within these two layers, it was confirmed that the magnetic energy released during the flux cancellation can support heating in the aforesaid height range. Further, the temperature stratification maps enabled us to identify cumulative effects of successive reconnection on temperature pattern, including recurring temperature enhancements. Similarly, Doppler velocity stratification maps revealed impacts on plasma flow pattern, such as a sudden change in the flow direction.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Made-to-measure modelling of globular clusters

Pages: 3898 - 3908
Abstract: ABSTRACTWe present the first application of the made-to-measure method for modelling dynamical systems to globular clusters. Through the made-to-measure algorithm, the masses of individual particles within a model cluster are adjusted while the system evolves forward in time via a gravitational N-body code until the model cluster is able to reproduce select properties of an observed cluster. The method is first applied to observations of mock isotropic and anisotropic clusters while fitting against the cluster’s 3D or projected density profile, density weighted mean-squared velocity profile, or its density profile with individual mean-squared velocity profiles assuming $10 {{\ \rm per\ cent}}$ uncertainty in each of these observables. We find that a cluster’s 3D density profile can easily be reproduced by the made-to-measure method, with minor discrepancies in the outer regions if fitting against a cluster’s projected surface density or projected kinematic properties. If an observed cluster is anisotropic, only fitting against the cluster’s density profile and individual mean-squared velocity profiles will fully recover the full degree of anisotropy. Partial anisotropy can be recovered as long as two kinematic properties are included in the fit. We further apply the method to observations of the Galactic globular cluster M4 and generate a complete 6D representation of the cluster that reproduces observations of its surface density profile, mean-squared proper motion velocity profile, and mean-squared line of sight velocity profile. The M2M method predicts M4 is primarily isotropic with a mass of $9.2\pm 0.4\times 10^4\, \mathrm{ M}_{\odot }$ and a half-mass radius of 3.7 ± 0.1 pc.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Gamma-ray bursts, quasars, baryonic acoustic oscillations, and supernovae
Ia: new statistical insights and cosmological constraints

Pages: 3909 - 3924
Abstract: ABSTRACTThe recent $\sim 4 \, \sigma$ Hubble constant, H0, tension is observed between the value of H0 from the cosmic microwave background (CMB) and Type Ia supernovae (SNe Ia). It is a decade since this tension is excruciating the modern astrophysical community. To shed light on this problem is key to consider probes at intermediate redshifts between SNe Ia and CMB and reduce the uncertainty on H0. Toward these goals, we fill the redshift gap by employing gamma-ray bursts (GRBs) and quasars (QSOs), reaching z = 9.4 and z = 7.6, respectively, combined with baryonic acoustic oscillations (BAO), and SNe Ia. To this end, we employ the ‘Dainotti GRB 3D relation’ among the rest-frame end time of the X-ray plateau emission, its corresponding luminosity, and the peak prompt luminosity, and the ‘Risaliti–Lusso’ QSO relation between ultraviolet and X-ray luminosities. We inquire the commonly adopted Gaussianity assumption on GRBs, QSOs, and BAO. With the joint sample, we fit the flat Λ Cold Dark Matter model with both the Gaussian and the newly discovered likelihoods. We also investigate the impact of the calibration assumed for Pantheon and Pantheon  + SNe Ia on this analysis. Remarkably, we show that only GRBs fulfil the Gaussianity assumption. We achieve small uncertainties on the matter-density parameter ΩM and H0. We find H0 values compatible within 2σ with the one from the Tip of the Red Giant Branch. Finally, we show that the cosmological results are heavily biased against the arbitrary calibration choice for SNe Ia.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• A method of photometric data extraction for asteroids from time-domain
surveys

Pages: 3925 - 3938
Abstract: ABSTRACTThe lightcurves of asteroids are essential for determining their physical characteristics, including shape, spin, size, and surface composition. However, most asteroids are missing some of these basic physical parameters due to lack of photometric data. Although a few telescopes or surveys are specially designed for photometric lightcurve observations of asteroids, many ground-based and space-based sky surveys for hunting new exoplanets, transient events, etc., should capture numerous small Solar system objects. This will benefit the physical studies of these objects. In order to extract data of these moving objects from time-domain photometric surveys, we have developed a new method using the model tree algorithm in the field of machine learning. A dedicated module is built to automatically identify moving objects in data set and extract their photometric and astrometric data. As the first application of this novel method, we have analysed data in five fields of the Yunnan-Hong Kong wide field photometric (YNHK) survey, from which 538 lightcurves of 211 asteroids are successfully extracted. Meanwhile, we also tested the method based on the data from NASA’s Transiting Exoplanet Survey Satellite, and the result proves the reliability of our method. With derived lightcurves of 13 asteroids from the YNHK survey, we have determined their synodic spin periods, among which the periods of four asteroids are estimated for the first time. In future, we are going to apply this method to search for small objects in the outer part of the Solar system from the Chinese Space Station Telescope survey.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• A closer look at dark photon explanations of the excess radio background

Pages: 3939 - 3950
Abstract: ABSTRACTThe observed excess radio background has remained a puzzle for over a decade. A recent new physics solution involves dark matter that decays into dark photons in the presence of a thermal dark photon background. The produced non-thermal dark photon spectrum then converts into standard photons around the reionization era, yielding an approximate power-law radio excess with brightness temperature T(ν) ≃ ν−2.5 over a wide range of frequencies, ν. This simple power-law model comes intriguingly close to the current data, even if several ingredients are required to make it work. In this paper, we investigate some of the details of this model, showcasing the importance of individual effects. In particular, significant deviation from a power law is present at $\nu \lesssim 100\, {\rm MHz}$ and $\nu \gtrsim 1\, {\rm GHz}$. These effects result in improving the fit to data compared to a power-law spectrum, and may become testable in future observations. We also highlight independent signatures that can be tested with future cosmic microwave background spectral distortion experiments such as PIXIE. However, there are challenges for the model from the observed radio background anisotropies, as discussed here. We furthermore highlight a possible runaway process due to the finite width of the dark matter decay profile, which suggests that additional work might be required to obtain a viable model.
PubDate: Thu, 16 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• On the cyclotron absorption line and evidence of the spectral transition
in SMC X-2 during 2022 giant outburst

Pages: 3951 - 3961
Abstract: ABSTRACTWe report comprehensive spectral and temporal properties of the Be/X-ray binary pulsar SMC X-2 using X-ray observations during the 2015 and 2022 outbursts. The pulse profile of the pulsar is unique and strongly luminosity dependent. It evolves from a broad-humped into a double-peaked profile above luminosity 3 × 1038 erg s−1. The pulse fraction of the pulsar is found to be a linear function of luminosity as well as energy. We also studied the spectral evolution of the source during the latest 2022 outburst with NICER. The observed photon index shows a negative and positive correlation below and above the critical luminosity, respectively, suggesting evidence of spectral transition from the sub-critical to supercritical regime. The broad-band spectroscopy of four sets of NuSTAR and XRT/NICER data from both outbursts can be described using a cut-off power-law model with a blackbody component. In addition to the 6.4 keV iron fluorescence line, an absorption-like feature is clearly detected in the spectra. The cyclotron line energy observed during the 2015 outburst is below 29.5 keV, however latest estimates in the 2022 outburst suggest a value of 31.5 keV. Moreover, an increase of 3.4 keV is detected in the cyclotron line energy at equal levels of luminosity observed in 2022 with respect to 2015. The observed cyclotron line energy variation is explored in terms of accretion induced screening mechanism or geometrical variation in line forming region.
PubDate: Thu, 16 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Scattering of light in thin magnetized envelopes – II

Pages: 3962 - 3971
Abstract: ABSTRACTWe consider optically thin spherical stellar envelopes with dipole magnetic field. The source of magnetic dipole field is assumed point like and emits the non-polarized monochromatic radiation. This paper carry on the previous paper of authors, where the general theory is presented and the circular polarization of scattered radiation is calculated for small values of magnetic fields corresponding to parameter x ≪ 1 (x = ωB/ω ≃ 0.933 × 10−8λ(μm)B(G)). The Stokes parameters of scattered radiation mutually transform into each other due to interference. Here we obtained the explicit formulas describing the transformation of all Stokes parameters for any value of parameter x. The qualitative discussion of these formulas is presented. These formulas show that for x ∼ 1 the transformation leads to large variations of all Stokes parameters. The linear and circular polarizations acquire oscillating dependence on the propagation path. For x ≫ 1 the single scattered radiation has very small circular polarization of the order ∼1/x ≪ 1 and large linear polarization. In this case the transformation gives rise to additional value of observed circular polarization, which is proportional to initial single scattered value. The observed linear polarization acquires small inclination angle relative to the plane ‘line of sight–direction of magnetic dipole’ due to existence of small circular polarization. The Stokes parameters of single scattered radiation from all envelope without taking into account the interference effects are given for x ≫ 1.
PubDate: Thu, 16 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The physical origin of supercompetitive accretion during the formation of
the first supermassive black holes

Pages: 3972 - 3980
Abstract: ABSTRACTNumerical simulations have shown the occurrence of a scenario termed ‘supercompetitive accretion’, a term that describes a situation where only the central few objects grow supermassive while a larger number of stars compete for the reservoir, with significant accretion flows of ≳0.1 M⊙ yr−1. This scenario particularly implies that the presence of fragmentation will not necessarily impeed the formation of a central massive object. We, here, explore this phenomenon using analytical estimates for growth via collisions and accretion, considering accretion due to self-gravity as well as Bondi–Hoyle accretion. Particularly, we explore under what conditions the accretion on to the central massive object breaks down, and derive a criterion that depends on the mass of the most massive object and the mass in fragments. For compact clusters with sizes about 0.1 pc, we further find that the mass growth by collisions is comparable to the growth via accretion. Our results are validated through the comparison with numerical simulations, and we overall conclude that supercompetitive accretion is a valid mechanism for the formation of very massive objects in the early Universe.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Accurate model of the projected velocity distribution of galaxies in dark
matter haloes

Pages: 3981 - 3990
Abstract: ABSTRACTWe present a per cent-level accurate model of the line-of-sight velocity distribution of galaxies around dark matter haloes as a function of projected radius and halo mass. The model is developed and tested using synthetic galaxy catalogues generated with the UniverseMachine run on the Multi-Dark Planck 2 N-body simulations. The model decomposes the galaxies around a cluster into three kinematically distinct classes: orbiting, infalling, and interloping galaxies. We demonstrate that: (1) we can statistically distinguish between these three types of galaxies using only projected line-of-sight velocity information; (2) the halo edge radius inferred from the line-of-sight velocity dispersion is an excellent proxy for the three-dimensional halo edge radius; and (3) we can accurately recover the full velocity dispersion profile for each of the three populations of galaxies. Importantly, the velocity dispersion profiles of the orbiting and infalling galaxies contain five independent parameters – three distinct radial scales and two velocity dispersion amplitudes – each of which is correlated with mass. Thus, the velocity dispersion profile of galaxy clusters has inherent redundancies that allow us to perform non-trivial systematics checks from a single data set. We discuss several potential applications of our new model for detecting the edge radius and constraining cosmology and astrophysics using upcoming spectroscopic surveys.
PubDate: Fri, 24 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Evidence for a bottom-light initial mass function in massive star clusters

Pages: 3991 - 4008
Abstract: ABSTRACTWe have determined stellar mass functions of 120 Milky Way globular clusters and massive Large Magellanic Cloud/Small Magellanic Cloud star clusters based on a comparison of archival Hubble Space Telescope photometry with a large grid of direct N-body simulations. We find a strong correlation of the global mass function slopes of star clusters with both their internal relaxation times and their lifetimes. Once dynamical effects are being accounted for, the mass functions of most star clusters are compatible with an initial mass function described by a broken power-law distribution N(m) ∼ mα with break masses at 0.4 and 1.0 M⊙ and mass function slopes of αLow = −0.3 for stars with masses m < 0.4 M⊙, αHigh = −2.30 for stars with m > 1.0 M⊙, and αMed = −1.65 for intermediate-mass stars. Alternatively, a lognormal mass function with a characteristic mass log MC = −0.36 and width σC = 0.28 for low-mass stars and a power-law mass function for stars with m > 1 M⊙ also fit our data. We do not find a significant environmental dependence of the initial mass function on cluster mass, density, global velocity dispersion, or metallicity. Our results lead to a larger fraction of high-mass stars in globular clusters compared to canonical Kroupa/Chabrier mass functions, increasing the efficiency of self-enrichment in clusters and helping to alleviate the mass budget problem of multiple stellar populations in globular clusters. By comparing our results with direct N-body simulations, we finally find that only simulations in which most black holes are ejected by natal birth kicks correctly reproduce the observed correlations.
PubDate: Wed, 01 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• New dwarf galaxy candidates in the sphere of influence of the Local Volume
spiral galaxy NGC2683

Pages: 4009 - 4023
Abstract: ABSTRACTWe present initial results of a survey of host L* galaxies environments in the Local Volume ($D\lt 10\,$ Mpc) searching for satellite dwarf galaxy candidates using the wide-field Hyper Suprime-Cam imager on the 8 m Subaru Telescope. This paper presents complete results on NGC2683 ($M_{B_T,0}=-19.62$, $D=9.36\, \mathrm{ Mpc}$, $v_{\odot }=411\, \mathrm{ km\, s}^{-1}$), an isolated Sc spiral galaxy in the Leo Spur. At the distance of NGC2683, we image the complete volume out to projected radii of $380\, \mathrm{ kpc}$ using a hexagonal arrangement of 7 pointings. Direct inspection of the images is complete down to Mg ∼ −11 and has revealed four new satellite galaxy candidates, two of which have been independently discovered by other researchers. Assuming the distance of NGC2683, these candidates span luminosities −12 < Mg < −9 and effective radii 150 pc <re < 1100 pc and are found to be morphologically reminiscent of satellite galaxies in the Local Group. These four new candidates add to the eight already known. A principle component analysis of the 2D projected distribution of the 12 satellite galaxies of NGC2683 reveals a flattened projected disc of satellites, with axis ratio b/a = 0.23. This flattening in the 2D projected system of satellites is a 1 per cent outlier of simulated isotropic satellite systems but is mostly consistent with satellite distributions of comparable galaxy environments in the IllustrisTNG simulation. This indicates the possible presence of a satellite plane, which will need to be investigated with follow-up observations.
PubDate: Thu, 09 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Stellar prospects for FRB gravitational lensing

Pages: 4024 - 4038
Abstract: ABSTRACTGravitational lensing of fast radio bursts (FRBs) offers an exciting avenue for several cosmological applications. However, it is not yet clear how many such events future surveys will detect nor how to optimally find them. We use the known properties of FRBs to forecast detection rates of gravitational lensing on delay time-scales from microseconds to years, corresponding to lens masses spanning 15 orders of magnitude. We highlight the role of the FRB redshift distribution on our ability to observe gravitational lensing. We consider cosmological lensing of FRBs by stars in foreground galaxies and show that strong stellar lensing will dominate on microsecond time-scales. Upcoming surveys such as DSA-2000 and CHORD will constrain the fraction of dark matter in compact objects (e.g. primordial black holes) and may detect millilensing events from intermediate mass black holes (IMBHs) or small dark matter halos. Coherent all-sky monitors will be able to detect longer-duration lensing events from massive galaxies, in addition to short time-scale lensing. Finally, we propose a new application of FRB gravitational lensing that will measure directly the circumgalactic medium of intervening galaxies.
PubDate: Thu, 09 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Population III X-ray binaries and their impact on the early universe

Pages: 4039 - 4055
Abstract: ABSTRACTThe first population of X-ray binaries (XRBs) is expected to affect the thermal and ionization states of the gas in the early Universe. Although these X-ray sources are predicted to have important implications for high-redshift observable signals, such as the hydrogen 21-cm signal from cosmic dawn and the cosmic X-ray background, their properties are poorly explored, leaving theoretical models largely uninformed. In this paper we model a population of X-ray binaries arising from zero metallicity stars. We explore how their properties depend on the adopted initial mass function (IMF) of primordial stars, finding a strong effect on their number and X-ray production efficiency. We also present scaling relations between XRBs and their X-ray emission with the local star formation rate, which can be used in sub-grid models in numerical simulations to improve the X-ray feedback prescriptions. Specifically, we find that the uniformity and strength of the X-ray feedback in the intergalactic medium is strongly dependant on the IMF. Bottom-heavy IMFs result in a smoother distribution of XRBs, but have a luminosity orders of magnitude lower than more top-heavy IMFs. Top-heavy IMFs lead to more spatially uneven, albeit strong, X-ray emission. An intermediate IMF has a strong X-ray feedback while sustaining an even emission across the intergalactic medium. These differences in X-ray feedback could be probed in the future with measurements of the cosmic dawn 21-cm line of neutral hydrogen, which offers us a new way of constraining population III IMF.
PubDate: Fri, 10 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Forecasting constraints on the mean free path of ionizing photons at z ≥
5.4 from the Lyman-α forest flux autocorrelation function

Pages: 4056 - 4073
Abstract: ABSTRACTFluctuations in Lyman-α (Ly α) forest transmission towards high-z quasars are partially sourced from spatial fluctuations in the ultraviolet background, the level of which are set by the mean free path of ionizing photons (λmfp). The autocorrelation function of Ly α forest flux characterizes the strength and scale of transmission fluctuations and, as we show, is thus sensitive to λmfp. Recent measurements at z ∼ 6 suggest a rapid evolution of λmfp at z > 5.0 which would leave a signature in the evolution of the autocorrelation function. For this forecast, we model mock Ly α forest data with properties similar to the XQR-30 extended data set at 5.4 ≤ z ≤ 6.0. At each z, we investigate 100 mock data sets and an ideal case where mock data matches model values of the autocorrelation function. For ideal data with λmfp = 9.0 cMpc at z = 6.0, we recover $\lambda _{\text{mfp}}=12^{+6}_{-3}$ cMpc. This precision is comparable to direct measurements of λmfp from the stacking of quasar spectra beyond the Lyman limit. Hypothetical high-resolution data leads to a $\sim 40~{{\ \rm per\ cent}}$ reduction in the error bars over all z. The distribution of mock values of the autocorrelation function in this work is highly non-Gaussian for high-z, which should caution work with other statistics of the high-z Ly α forest against making this assumption. We use a rigorous statistical method to pass an inference test, however future work on non-Gaussian methods will enable higher precision measurements.
PubDate: Tue, 07 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Can radial motions in the stellar halo constrain the rate of change of
mass in the Galaxy'

Pages: 4074 - 4084
Abstract: ABSTRACTA change in the mass of the Galaxy with time will leave its imprint on the motions of the stars, with stars having radially outward (mass-loss) or inward (mass accretion) bulk motions. Here, we test the feasibility of using the mean radial motion of stars in the stellar halo to constrain the rate of change of mass in the Galaxy, e.g. due to decay of dark matter. In the lambda cold dark matter (ΛCDM) paradigm, the stellar halo is formed by accretion of satellites on to the host galaxy and its mean radial motion 〈VR〉 is eventually expected to be close to zero. But due to incomplete mixing most haloes have substructures and this can lead to non-zero 〈VR〉 in them. Using simulations, we measure the mean radial motion of stars in 13 ΛCDM stellar haloes lying in a spherical shell of radius 30 kpc. For most haloes, the shell motion is quite small, with 75 per cent of haloes having $\langle V_\text{R}\rangle \lesssim 1.2 \:{\rm km}\, {\rm s}^{-1}$. When substructures are removed by using a clustering algorithm, 〈VR〉 is reduced even further, with 75 per cent of haloes having $\langle V_\text{R}\rangle \lesssim 0.6 \:{\rm km}\, {\rm s}^{-1}$. A value of $\langle V_\text{R}\rangle \approx 0.6 \:{\rm km}\, {\rm s}^{-1}$ can be attained corresponding to a galactic mass-loss rate of 2 per cent per Gyr. We show that this can place constraints on dark matter decay parameters such as the decay lifetime and the kick velocity that is imparted to the daughter particle. The advent of all-sky stellar surveys involving millions to billions of stars is encouraging for detecting signatures of dark matter decay.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The strong effect of electron thermal conduction on the global structure
of the heliosphere

Pages: 4085 - 4090
Abstract: ABSTRACTVoyager 1 and 2 crossed the heliopause at ∼122 au in 2012 and ∼119 au in 2018, respectively. It was quite a surprise because the thickness of the inner heliosheath obtained at that time by the existing time models of the global heliosphere was significantly larger (by 20–40 au). Until now, the problem of the heliosheath thickness has not been fully resolved. Earlier, in the frame of an oversimplified toy model of nearly isothermal solar wind plasma, it has been shown that the effect of electron thermal conduction may significantly reduce the thickness of the inner heliosheath. In this paper, we present the first results of our 3D kinetic-magnetohydrodynamic (MHD) model of the global heliosphere, where the effect of thermal electron conduction has been considered rigorously. The thermal conduction acts mainly along the magnetic field lines. Classical and saturated thermal fluxes are employed when appropriate. It is shown that the effects of thermal conduction are significant. The thickness of the inner heliospheric is reduced. It is a desired effect since it helps to reconcile the thickness obtained in the model with Voyager data. The other effects are the strong depletion of the heliosheath plasma temperature towards the heliopause and the increase of the plasma temperature in the supersonic solar wind upstream of the termination shock.
PubDate: Sat, 11 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Phase synchronization of epicyclic motion due to gravitational scattering
by wakes

Pages: 4091 - 4099
Abstract: ABSTRACTThe swing amplification is one of the mechanisms for spiral arm formation and gravitational scattering of stellar orbits by a high-density region in a disc galaxy is considered as its elementary process. During the swing amplification, the epicycle phases of stars are synchronized. We previously showed that gravitational scattering by a softened point mass can synchronize the epicycle phases. Here, we expand upon our previous work to consider gravitational scattering by a finite-sized wake, which we model by using a prolate body. We numerically simulate the stellar motion under the influence of the wake gravity, and we investigate the dependence of the orbital evolution on the wake properties. We find that phase synchronization is more effective for a wake with a pitch angle around π/2, and that the phase synchronization depends on the wake shape. Even for realistic pitch angles i ≲ π/4 the phase synchronization can be more effective than that by the softened point mass. Increasing the impact parameter of stars and decreasing the wake pitch angle are shown to increase the axis ratio at which synchronization occurs. Linear trailing high-density patterns form around the wake and enlarge the wake itself.
PubDate: Tue, 14 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Nested sampling statistical errors

Pages: 4100 - 4108
Abstract: ABSTRACTNested sampling (NS) is a popular algorithm for Bayesian computation. We investigate statistical errors in NS both analytically and numerically. We show two analytic results. First, we show that the leading terms in Skilling’s expression using information theory match the leading terms in Keeton’s expression from an analysis of moments. This approximate agreement was previously only known numerically and was somewhat mysterious. Second, we show that the uncertainty in single NS runs approximately equals the standard deviation in repeated NS runs. While intuitive, this was previously taken for granted. We close by investigating our results and their assumptions in several numerical examples, including cases in which NS uncertainties increase without bound.
PubDate: Wed, 15 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Contrasting X-ray/UV time-lags in Seyfert 1 galaxies NGC 4593 and NGC 7469
using AstroSat observations

Pages: 4109 - 4121
Abstract: ABSTRACTWe study accretion disc–corona connection in Seyfert 1 galaxies using simultaneous UV/X-ray observations of NGC 4593 (2016 July 14–18) and NGC 7469 (2017 October 15–19) performed with AstroSat. We use the X-ray (0.5–7.0 keV) data acquired with the Soft X-ray Telescope (SXT) and the UV (FUV: 130–180 nm, NUV: 200–300 nm) data obtained with the Ultra-Violet Imaging Telescope (UVIT). We also use the contemporaneous Swift observations of NGC 4593 and demonstrate AstroSat’s capability for X-ray/UV correlation studies. We performed UV/X-ray cross-correlation analysis using the interpolated and the discrete cross-correlation functions and found similar results. In the case of NGC 4593, we found that the variations in the X-rays lead to those in the FUV and NUV bands by ∼38 ks and ∼44 ks, respectively. These UV lags favour the disc-reprocessing model; they are consistent with the previous results within uncertainties. In contrast, we found an opposite trend in NGC 7469 where the soft X-ray variations lag those in the FUV and NUV bands by ∼41 ks and ∼49 ks, respectively. The hard lags in NGC 7469 favour the thermal Comptonization model. Our results may provide direct observational evidence for the variable intrinsic UV emission from the accretion disk, which acts as the seed for thermal Comptonization in a hot corona in a lamp-post-like geometry. The non-detection of disk reverberation photons in NGC 7469, using AstroSat data, is most likely due to a high accretion rate resulting in a hot accretion disc and large intrinsic emission.
PubDate: Wed, 15 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Constraining the rotation profile in a low-luminosity subgiant with a
surface rotation measurement

Pages: 4122 - 4130
Abstract: ABSTRACTRotationally induced mode splitting frequencies of low-luminosity subgiants suggest that angular momentum transport mechanisms are 1–2 orders of magnitude more efficient in these stars than predicted by theory. Constraints on the rotation profile of low-luminosity subgiants could be used to identify the dominant mechanism for angular momentum transport. We develop a forward model for the rotation profile given observed rotational splittings, assuming a step-like rotation profile. We identify a consistent degeneracy between the position of the profile discontinuity and the surface rotation rate. We perform mock experiments that show the discontinuity position can be better constrained with a prior on the surface rotation rate, which is informed by star spot modulations. We finally apply this approach to KIC 12508433, a well-studied low-luminosity subgiant, as an example case. With the observed surface rotation prior, we obtain a factor of 2 increase in precision of the position of strong rotation gradient. We recover the literature values of the core and surface rotation rates and find the highest support for a discontinuity in the radiative zone. Auxiliary measurements of surface rotation could substantially improve inferences on the rotation profile of low-luminosity subgiants with already available data.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Study with WhoSGlAd of the acoustic depth of the helium glitch across the
seismic HR diagram and its impact on the inferred helium abundance

Pages: 4131 - 4139
Abstract: ABSTRACTThe acoustic glitches’ signature present in solar-like stars holds invaluable information. Indeed, it is caused by a sharp variation in the sound speed, therefore carrying localized information. One such glitch is the helium glitch caused by the hydrogen and first and second partial helium ionization region, allowing us to constrain the surface helium abundance. However, the function adjusted to the glitch signature depends non-linearly on the acoustic depth at which it occurs, He. Retrieving the faint glitch signature and estimating τHe are difficult but crucial tasks to accurately measure the glitch parameters and, ultimately, accurately infer the helium abundance. In this paper, we aim at providing a way to estimate τHe using precise seismic indicators, independent of stellar modelling. Consequently, we aim at improving the WhoSGlAd (Whole Spectrum and Glitches Adjustment) method by automatically providing a model-independent measure of the glitch’s parameters. We compute the evolution of THe, a dimensionless form of the acoustic depth, along a grid of models and adjust an empirical linear relation between THe and the mean large separation and frequency ratio as defined in WhoSGlAd. We further optimize over the value of this estimate to ensure the stability and accuracy of the approach. The proposed approach provides an excellent estimate of the acoustic depth and allows us to swiftly retrieve the glitch signature of observed spectra. We demonstrate that the we can accurately model the helium abundance of four Kepler targets by comparing model (both versions of WhoSGlAd) and literature values.
PubDate: Thu, 16 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Efficient exploration of reionization parameters for the upcoming 21 cm
observations using a photon-conserving seminumerical model SCRIPT

Pages: 4140 - 4155
Abstract: ABSTRACTOne of the most promising probes to constrain the reionization history of the universe is the power spectrum of neutral hydrogen 21 cm emission fluctuations. The corresponding analyses require computationally efficient modelling of reionization, usually achieved through seminumerical simulations. We investigate the capability of one such seminumerical code, SCRIPT, to constrain the reionization parameters. Our study involves creating a mock data set corresponding to the upcoming SKA-Low, followed by a Bayesian inference method to constrain the model parameters. In particular, we explore in detail whether the inferred parameters are unbiased with respect to the inputs used for the mock and also if the inferences are insensitive to the resolution of the simulation. We find that the model is successful on both fronts. We also develop a simple template model of reionization that can mimic the complex physical processes like inhomogeneous recombinations and radiative feedback and show that it can recover the global reionization history reliably with a moderate computational cost. However, such simple models are not suitable for constraining the properties of the ionizing sources. Our results are relevant for constraining reionization using high-quality data expected in the future telescopes.
PubDate: Thu, 16 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Redshift prediction of Fermi-LAT gamma-ray sources using catboost gradient
boosting decision trees

Pages: 4156 - 4161
Abstract: ABSTRACTThe determination of distance is fundamental in astrophysics. Gamma-ray sources are poorly characterized in this sense, as the limited angular resolution and poor photon-count statistics in gamma-ray astronomy makes it difficult to associate them to a multiwavelength object with known redshift. Taking the 1794 active galactic nuclei (AGNs) with known redshift from the Fermi-LAT latest AGN catalogue, 4LAC–DR3, we employ machine learning techniques to predict the distance of the rest of AGNs based on their spectral and spatial properties. The state-of-the-art catboost algorithm reaches an average 0.56 R2 score with 0.46 root-mean-squared error, predicting an average redshift value of zavg = 0.63, with a maximum zmax = 1.97. We use the shap explainer package to gain insights into the variables influence on the outcome, and also study the extragalactic background light implications. In a second part, we use this regression model to predict the redshift of the unassociated sample of the latest LAT point-source catalogue, 4FGL–DR3, using the results of a previous paper to determine the possible AGNs within them.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Collision excitation of nitrous acid (HONO) by helium: isomerization
effect

Pages: 4162 - 4172
Abstract: ABSTRACTWe generated new 3D-potential energy surfaces (3D-PESs) for the cis-HONO–He and trans-HONO–He weakly bound complexes along the intermonomer coordinates. We used the explicitly correlated Coupled Clusters with single, double, and perturbative triple excitations (CCSD(T)-F12) approach for the electronic structure computations, where the atoms were described using the aug-cc-pVTZ basis set. Then, we derived analytical forms for each PES. These PESs exhibit different shapes and present strong anisotropies. After quantum close-coupling scattering calculations for the lower rotational levels (up to ${9}_{2,7}$), and the coupled-states approximation for higher levels (up to ${22}_{1,22}$) using these PESs, we derived the collisional excitation cross sections of cis-HONO and trans-HONO by He for total energies 0.1 ≤ E ≤ 900 cm−1 and the rate coefficients for kinetic temperatures T ≤ 100 K. Our work shows that the collision data of cis-HONO and trans-HONO are different mainly because of the different 3D-PESs since the rotational energy structures of both isomers are very similar. Also, computations show that the data of the non-detected cis-HONO are as large as those of the detected trans-HONO isomer. They confirm the large values for the detected transition 52,4 → 41,3 of trans-HONO. Therefore, our work strongly suggests revisiting radiative transfer calculations to determine accurately the population of the rotational levels of these isomers. Our work should help astrophysicists for the detectability of such nitrogen oxide molecules and for the possible formation mechanisms and isomerization pathways specificities.
PubDate: Wed, 22 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Stellar mass, not dynamical mass nor gravitational potential, drives the
mass–metallicity relationship

Pages: 4173 - 4179
Abstract: ABSTRACTThe widely known relation between stellar mass and gas metallicity [mass–metallicity relation (MZR)] in galaxies is often ascribed to the higher capability of more massive systems to retain metals against the action of galactic outflows. In this scenario the stellar mass would simply be an indirect proxy of the dynamical mass or of the gravitational potential. We test this scenario by using a sample of more than 1000 star-forming galaxies from the MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) survey for which dynamical masses have been accurately determined. By using three different methods (average dispersion, partial correlation coefficients, and random forest), we unambiguously find that the gas metallicity depends primarily and fundamentally on the stellar mass. Once the dependence on stellar mass is taken into account, there is little or no dependence on either dynamical mass or gravitational potential (and, if anything, the metallicity dependence on the latter quantities is inverted). Our result indicates that the MZR is not caused by the retention of metals in more massive galaxies. The direct, fundamental dependence of metallicity on stellar mass suggests the much simpler scenario in which the MZR is just a consequence of the stellar mass being proportional to the integral of metals production in the galaxy.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Radio emission of tidal disruption events from wind–cloud
interaction

Pages: 4180 - 4189
Abstract: ABSTRACTWinds can be launched in tidal disruption event (TDE). It has been proposed that the winds can interact with the cloud surrounding the black hole, produce bow shocks, accelerate electrons, and produce radio emission. We restudy the wind–cloud interaction model. We employ the properties of winds found by the radiation hydrodynamic simulations of super-Eddington circularized accretion flow in TDEs. We can calculate the peak radio emission frequency, the luminosity at the peak frequency, and their time-evolution based on the TDEs wind–cloud interaction model. We find that the model predicted peak radio emission frequency, the luminosity at peak frequency, and their time evolution can be well consistent with those in TDEs AT2019dsg and ASASSN-14li. This indicates that in these two radio TDEs, the wind–cloud interaction mechanism may be responsible for the radio emission.
PubDate: Fri, 17 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The origin of optical emission lines in the soft state of X-ray binary
outbursts: the case of MAXI J1820+070

Pages: 4190 - 4206
Abstract: ABSTRACTThe optical emission line spectra of X-ray binaries (XRBs) are thought to be produced in an irradiated atmosphere, possibly the base of a wind, located above the outer accretion disc. However, the physical nature of – and physical conditions in – the line-forming region remain poorly understood. Here, we test the idea that the optical spectrum is formed in the transition region between the cool geometrically thin part of the disc near the mid-plane and a hot vertically extended atmosphere or outflow produced by X-ray irradiation. We first present a VLT X-Shooter spectrum of XRB MAXI J1820+070 in the soft state associated with its 2018 outburst, which displays a rich set of double-peaked hydrogen and helium recombination lines. Aided by ancillary X-ray spectra and reddening estimates, we then model this spectrum with the Monte Carlo radiative transfer code python, using a simple biconical disc wind model inspired by radiation-hydrodynamic simulations of irradiation-driven outflows from XRB discs. Such a model can qualitatively reproduce the observed features; nearly all of the optical emission arising from the transonic ‘transition region’ near the base of the wind. In this region, characteristic electron densities are on the order of 1012–13 cm−3, in line with the observed flat Balmer decrement (H $\alpha$/H $\beta$ ≈ 1.3). We conclude that strong irradiation can naturally give rise to both the optical line-forming layer in XRB discs and an overlying outflow/atmosphere that produces X-ray absorption lines.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Age-divided mean stellar populations from full spectrum fitting as the
simplified star formation and chemical evolution history of a galaxy:
methodology and reliability

Pages: 4207 - 4232
Abstract: ABSTRACTWe introduce a practical methodology for investigating the star formation and chemical evolution history of a galaxy: age-divided mean stellar populations (ADPs) from full spectrum fitting. In this method, the mass-weighted mean stellar populations and mass fractions (fmass) of young and old stellar components in a galaxy are separately estimated, which are divided with an age cut (selected to be 109.5 yr ≈3.2 Gyr in this paper). To examine the statistical reliability of ADPs, we generate 10 000 artificial galaxy spectra, each of which consists of five random simple stellar population components. Using the Penalized PiXel-Fitting (ppxf) package, we conduct full spectrum fitting to the artificial spectra with noise as a function of wavelength, imitating the real noise of Sydney-Australian Astronomical Observatory Multi-object Integral field spectrograph (SAMI) galaxies. As a result, the Δ (= output − input) of age and metallicity appears to significantly depend on not only signal-to-noise ratio (S/N), but also luminosity fractions (flum) of young and old components. At given S/N and flum, Δ of young components tends to be larger than Δ of old components; e.g. σ(Δ[M/H]) ∼ 0.40 versus 0.23 at S/N = 30 and flum = 50 per cent. The age-metallicity degeneracy appears to be insignificant, but Δlog(age/yr) shows an obvious correlation with Δfmass for young stellar components ($\mathcal {R}\sim 0.6$). The impact of dust attenuation and emission lines appears to be mostly insignificant. We discuss how this methodology can be applied to spectroscopic studies of the formation histories of galaxies, with a few examples of SAMI galaxies.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The effects of time-variable absorption due to gamma-ray bursts in active
galactic nucleus accretion discs

Pages: 4233 - 4245
Abstract: ABSTRACTBoth long and short gamma-ray bursts (GRBs) are expected to occur in the dense environments of active galactic nucleus (AGN) accretion discs. As these bursts propagate through the discs they live in, they photoionize the medium causing time-dependent opacity that results in transients with unique spectral evolution. In this paper, we use a line-of-sight radiation transfer code coupling metal and dust evolution to simulate the time-dependent absorption that occurs in the case of both long and short GRBs. Through these simulations, we investigate the parameter space in which dense environments leave a potentially observable imprint on the bursts. Our numerical investigation reveals that time-dependent spectral evolution is expected for central supermassive black hole masses between 105 and 5 × 107 solar masses in the case of long GRBs, and between 104 and 107 solar masses in the case of short GRBs. Our findings can lead to the identification of bursts exploding in AGN disc environments through their unique spectral evolution coupled with a central location. In addition, the study of the time-dependent evolution would allow for studying the disc structure, once the identification with an AGN has been established. Finally, our findings lead to insight into whether GRBs contribute to the AGN emission, and which kind, thus helping to answer the question of whether GRBs can be the cause of some of the as-of-yet unexplained AGN time variability.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Correction to: PINION: physics-informed neural network for accelerating
radiative transfer simulations for cosmic reionization

Pages: 4246 - 4246
Abstract: This is a correction to: Damien Korber, Michele Bianco, Emma Tolley, Jean-Paul Kneib, PINION: physics-informed neural network for accelerating radiative transfer simulations for cosmic reionization, Monthly Notices of the Royal Astronomical Society, Volume 521, Issue 1, May 2023, Pages 902–915, https://doi.org/10.1093/mnras/stad615.
PubDate: Tue, 28 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The vertex coordinates of the Galaxy’s stellar systems according to
the Gaia DR3 catalogue

Pages: 4247 - 4256
Abstract: ABSTRACTWe present the results of determining the coordinates of the vertices of various stellar systems, the centroids of which are located in the Galactic plane. To do this, the positions, parallaxes, proper motions, and radial velocities of red giants and subgiants contained in the Gaia DR3 catalogue have been used. When determining the components of the deformation velocity tensors in local coordinate systems, we found the coordinates of the vertices of the stellar systems under study. It turned out that there is a complex dependence of vertex deviations lxy in Galactocentric cylindrical (R, θ) and Galactic rectangular (X, Y) coordinates. Based on the approach proposed in this paper, heliocentric distances to vertices have been determined for the first time. The results obtained show that in addition to the fact that the angular coordinates of the Galactic Centre and the vertices of stellar systems do not coincide, their heliocentric distances do not coincide as well. This presumably indicates that there are structures in the Galaxy that noticeably affect its axisymmetry.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Periodic X-ray sources in the massive globular cluster 47 Tucanae:
Evidence for dynamically formed cataclysmic variables

Pages: 4257 - 4276
Abstract: ABSTRACTWe present a systematic study of periodic X-ray sources in the massive globular cluster 47 Tuc, utilizing deep archival Chandra observations that resolve the cluster core and recently available eROSITA observations that cover the cluster outskirt. By applying the Gregory-Loredo algorithm, we detect 20 periodic signals among 18 X-ray sources, ranging between 205–95731 s. Fourteen periods are newly discovered in the X-ray band. We classify these periodic sources into four quiescent low-mass X-ray binaries, 1 ms pulsar, two coronally-active binaries, and eleven cataclysmic variables (CVs) based on their X-ray temporal and spectral properties, as well as multiband information. Despite a small sample subject to potential selection bias against faint and non-magnetic CVs, the 11 CVs together define an orbital period distribution significantly different from that of the CVs previously found in the solar neighbourhood and the Galactic bulge. In particular, there exists in 47 Tuc an apparent paucity of short-period CVs below the period gap, which might be attributed to a high occupation fraction of non-magnetic CVs. Also characteristic of the 47 Tuc CVs are an overabundance of long-period CVs with a subgiant donor, a substantial fraction of CVs within the period gap, and a steep radial surface density profile. These are best understood as a group of CVs having recently formed via dynamical interactions in the dense cluster core. Despite sufficient sensitivity of the X-ray data, only one periodic source is found between one-third of the half-light radius and the tidal radius, the nature of which is unclear.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Wind-fed GRMHD simulations of Sagittarius A*: tilt and alignment of jets
and accretion discs, electron thermodynamics, and multiscale modelling of
the rotation measure

Pages: 4277 - 4298
Abstract: ABSTRACTWind-fed models offer a unique way to form predictive models of the accretion flow surrounding Sagittarius A*. We present 3D wind-fed magnetohydrodynamic (MHD) and general relativistic magnetohydrodynamic (GRMHD) simulations spanning the entire dynamic range of accretion from parsec scales to the event horizon. We expand on previous work by including non-zero black hole spin and dynamically evolved electron thermodynamics. Initial conditions for these simulations are generated from simulations of the observed Wolf–Rayet stellar winds in the Galactic Centre. The resulting flow tends to be highly magnetized (β ≈ 2) with an ∼r−1 density profile independent of the strength of magnetic fields in the winds. Our simulations reach the magnetically arrested disc (MAD) state for some, but not all cases. In tilted flows, standard and normal evolution (SANE) jets tend to align with the angular momentum of the gas at large scales, even if that direction is perpendicular to the black hole spin axis. Conversely, MAD jets tend to align with the black hole spin axis. The gas angular momentum shows similar behaviour: SANE flows tend to only partially align while MAD flows tend to fully align. With a limited number of dynamical free parameters, our models can produce accretion rates, 230 GHz flux, and unresolved linear polarization fractions roughly consistent with observations for several choices of electron heating fraction. Absent another source of large-scale magnetic field, winds with a higher degree of magnetization (e.g. where the magnetic pressure is 1/100 of the ram pressure in the winds) may be required to get a sufficiently large rotation measure with consistent sign.
PubDate: Mon, 20 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• Conditions for clump survival in High-z disc galaxies

Pages: 4299 - 4322
Abstract: ABSTRACTWe study the survival of giant clumps in high-redshift disc galaxies, short-lived (S) versus long-lived (L), and two L subtypes, via analytic modelling and simulations. We develop a criterion for clump survival, with/without gas, based on a survivability parameter S. It compares the energy sources by supernova feedback and gravitational contraction to the clump binding energy and losses by outflows and turbulence dissipation. The clump properties are derived from Toomre instability, approaching virial/Jeans equilibrium, and the supernova energy deposit uses an up-to-date bubble analysis. For moderate feedback, we find L clumps with circular velocities ${\sim}50\, {\rm km}\, {\rm s}^{-1}$ and masses ≥108 M⊙. They favour galaxies with circular velocities ${\ge}200\, {\rm km\,s}^{-1}$, consistent at z ∼ 2 with the typical disc stellar mass, ≥109.3 M⊙. L clumps favour disc gas fractions ≥0.3, low-mass bulges, and z ∼ 2. They disfavour more effective feedback due to, e.g. supernova clustering, very strong radiative feedback, top-heavy stellar mass function, or particularly high star-formation-rate (SFR) efficiency. A subtype of L clumps (LS), which lose their gas in several free-fall times but retain bound stellar components, may be explained by less contraction and stronger gravitational effects, where clump mergers increase the SFR efficiency. These may give rise to globular clusters. The more massive L clumps (LL) retain most of their baryons for tens of free-fall times with a roughly constant star-formation rate.
PubDate: Tue, 21 Mar 2023 00:00:00 GMT
Issue No: Vol. 521, No. 3 (2023)

• The impact of time-dependent stellar activity on exoplanet atmospheres

Pages: 3333 - 3347
Abstract: ABSTRACTM-dwarfs are thought to be hostile environments for exoplanets. Stellar events are very common on such stars. These events might cause the atmospheres of exoplanets to change significantly over time. It is not only the major stellar flare events that contribute to this disequilibrium, but the smaller flares might also affect the atmospheres in an accumulating manner. In this study, we aim to investigate the effects of time-dependent stellar activity on the atmospheres of known exoplanets. We simulate the chemistry of GJ 876c, GJ 581c, and GJ 832c that go from H2-dominated to N2-dominated atmospheres using observed stellar spectra from the MUSCLES collaboration. We make use of the chemical kinetics code vulcan and implement a flaring routine that stochastically generates synthetic flares based on observed flare statistics. Using the radiative transfer code petitradtrans, we also simulate the evolution of emission and transmission spectra. We investigate the effect of recurring flares for a total of 11 d covering 515 flares. Results show a significant change in abundance for some relevant species such as H, OH, and CH4, with factors going up to three orders of magnitude difference with respect to the pre-flare abundances. We find a maximum change of ∼12 ppm for CH4 in transmission spectra on GJ 876c. These changes in the spectra remain too small to observe. We also find that the change in abundance and spectra of the planets accumulates throughout time, causing permanent changes in the chemistry. We conclude that this small but gradual change in chemistry arises due to the recurring flares.
PubDate: Fri, 28 Oct 2022 00:00:00 GMT
DOI: 10.1093/mnras/stac1220
Issue No: Vol. 521, No. 3 (2022)

• Origins of the UV/X-ray relation in Arakelian 120

Pages: 3585 - 3596
Abstract: ABSTRACTWe explore the accretion geometry in Arakelian 120 using intensive UV and X-ray monitoring from Swift. The hard X-rays (1–10 keV) show large amplitude, fast (few-day) variability, so we expect reverberation from the disc to produce UV variability from the varying hard X-ray illumination. We model the spectral energy distribution (SED) including an outer standard disc (optical), an intermediate warm-Comptonization region (UV and soft X-ray), and a hot corona (hard X-rays). Unlike the lower Eddington fraction AGN (NGC 4151 and NGC 5548 at L/LEdd ∼ 0.02 and 0.03, respectively), the SED of Akn 120 (L ∼ 0.05LEdd) is dominated by the UV, restricting the impact of reverberating hard X-rays by energetics alone. Illumination from a hard X-ray corona with height ∼10 Rg produces minimal UV variability. Increasing the coronal scale height to ∼100 Rg improves the match to the observed amplitude of UV variability as the disc subtends a larger solid angle, but results in too much fast variability to match the UV data. The soft X-rays (connected to the UV in the warm-Comptonization model) are more variable than the hard, but again contain too much fast variability to match the observed smoother variability seen in the UV. Results on lower Eddington fraction AGN have emphasized the contribution from reverberation from larger scales (the broad-line region), but reverberation induces lags on similar time-scales to the smoothing, producing a larger delay than is compatible with the data. We conclude that the majority of the UV variability is therefore intrinsic, connected to mass-accretion rate fluctuations in the warm-Comptonization region.
PubDate: Tue, 22 Feb 2022 00:00:00 GMT
DOI: 10.1093/mnras/stac3809
Issue No: Vol. 521, No. 3 (2022)

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