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  Subjects -> METEOROLOGY (Total: 110 journals)
Showing 1 - 36 of 36 Journals sorted alphabetically
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 3)
Advances in Atmospheric Sciences     Hybrid Journal   (Followers: 43)
Advances in Climate Change Research     Open Access   (Followers: 28)
Advances in Meteorology     Open Access   (Followers: 24)
Advances in Statistical Climatology, Meteorology and Oceanography     Open Access   (Followers: 7)
Aeolian Research     Hybrid Journal   (Followers: 6)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 18)
American Journal of Climate Change     Open Access   (Followers: 27)
Atmósfera     Open Access   (Followers: 3)
Atmosphere     Open Access   (Followers: 25)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 14)
Atmospheric and Oceanic Science Letters     Open Access   (Followers: 10)
Atmospheric Chemistry and Physics (ACP)     Open Access   (Followers: 47)
Atmospheric Chemistry and Physics Discussions (ACPD)     Open Access   (Followers: 14)
Atmospheric Environment     Hybrid Journal   (Followers: 72)
Atmospheric Environment : X     Open Access   (Followers: 3)
Atmospheric Research     Hybrid Journal   (Followers: 69)
Atmospheric Science Letters     Open Access   (Followers: 36)
Boundary-Layer Meteorology     Hybrid Journal   (Followers: 31)
Bulletin of Atmospheric Science and Technology     Hybrid Journal   (Followers: 1)
Bulletin of the American Meteorological Society     Open Access   (Followers: 49)
Carbon Balance and Management     Open Access   (Followers: 4)
Change and Adaptation in Socio-Ecological Systems     Open Access   (Followers: 4)
Ciencia, Ambiente y Clima     Open Access   (Followers: 3)
Climate     Open Access   (Followers: 5)
Climate Change Economics     Hybrid Journal   (Followers: 14)
Climate Change Research Letters     Open Access   (Followers: 7)
Climate Change Responses     Open Access   (Followers: 8)
Climate Dynamics     Hybrid Journal   (Followers: 44)
Climate law     Hybrid Journal   (Followers: 7)
Climate of the Past (CP)     Open Access   (Followers: 5)
Climate of the Past Discussions (CPD)     Open Access  
Climate Policy     Hybrid Journal   (Followers: 36)
Climate Research     Hybrid Journal   (Followers: 6)
Climate Risk Management     Open Access   (Followers: 4)
Climate Services     Open Access   (Followers: 3)
Climate Summary of South Africa     Full-text available via subscription   (Followers: 2)
Climatic Change     Open Access   (Followers: 60)
Current Climate Change Reports     Hybrid Journal   (Followers: 4)
Developments in Atmospheric Science     Full-text available via subscription   (Followers: 27)
Dynamics and Statistics of the Climate System     Open Access   (Followers: 5)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 18)
Earth Perspectives - Transdisciplinarity Enabled     Open Access  
Economics of Disasters and Climate Change     Hybrid Journal   (Followers: 2)
Energy & Environment     Hybrid Journal   (Followers: 23)
Environmental and Climate Technologies     Open Access   (Followers: 4)
Environmental Dynamics and Global Climate Change     Open Access   (Followers: 6)
Frontiers in Climate     Open Access   (Followers: 2)
GeoHazards     Open Access   (Followers: 1)
Global Meteorology     Open Access   (Followers: 17)
International Journal of Atmospheric Sciences     Open Access   (Followers: 21)
International Journal of Biometeorology     Hybrid Journal   (Followers: 1)
International Journal of Climatology     Hybrid Journal   (Followers: 31)
International Journal of Environment and Climate Change     Open Access   (Followers: 3)
International Journal of Image and Data Fusion     Hybrid Journal   (Followers: 2)
Journal of Agricultural Meteorology     Open Access  
Journal of Applied Meteorology and Climatology     Hybrid Journal   (Followers: 35)
Journal of Atmospheric and Oceanic Technology     Hybrid Journal   (Followers: 33)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 200)
Journal of Atmospheric Chemistry     Hybrid Journal   (Followers: 21)
Journal of Climate     Hybrid Journal   (Followers: 54)
Journal of Climate Change     Full-text available via subscription   (Followers: 2)
Journal of Climatology     Open Access   (Followers: 3)
Journal of Hydrology and Meteorology     Open Access   (Followers: 29)
Journal of Hydrometeorology     Hybrid Journal   (Followers: 11)
Journal of Integrative Environmental Sciences     Hybrid Journal   (Followers: 4)
Journal of Meteorological Research     Full-text available via subscription   (Followers: 1)
Journal of Meteorology and Climate Science     Full-text available via subscription   (Followers: 14)
Journal of Space Weather and Space Climate     Open Access   (Followers: 27)
Journal of the Atmospheric Sciences     Hybrid Journal   (Followers: 79)
Journal of the Meteorological Society of Japan     Partially Free   (Followers: 6)
Journal of Weather Modification     Full-text available via subscription   (Followers: 2)
Large Marine Ecosystems     Full-text available via subscription   (Followers: 1)
Mathematics of Climate and Weather Forecasting     Open Access   (Followers: 6)
Mediterranean Marine Science     Open Access   (Followers: 1)
Meteorologica     Open Access   (Followers: 2)
Meteorological Applications     Hybrid Journal   (Followers: 4)
Meteorological Monographs     Hybrid Journal  
Meteorologische Zeitschrift     Full-text available via subscription   (Followers: 3)
Meteorology and Atmospheric Physics     Hybrid Journal   (Followers: 26)
Mètode Science Studies Journal : Annual Review     Open Access  
Michigan Journal of Sustainability     Open Access   (Followers: 1)
Modeling Earth Systems and Environment     Hybrid Journal  
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 14)
Monthly Weather Review     Hybrid Journal   (Followers: 34)
Nature Climate Change     Full-text available via subscription   (Followers: 125)
Nature Reports Climate Change     Full-text available via subscription   (Followers: 35)
Nīvār     Open Access  
npj Climate and Atmospheric Science     Open Access   (Followers: 3)
Open Atmospheric Science Journal     Open Access   (Followers: 2)
Open Journal of Modern Hydrology     Open Access   (Followers: 6)
Revista Brasileira de Meteorologia     Open Access  
Revista Iberoamericana de Bioeconomía y Cambio Climático     Open Access  
Russian Meteorology and Hydrology     Hybrid Journal   (Followers: 3)
Space Weather     Full-text available via subscription   (Followers: 24)
Studia Geophysica et Geodaetica     Hybrid Journal  
Tellus A     Open Access   (Followers: 22)
Tellus B     Open Access   (Followers: 21)
The Cryosphere (TC)     Open Access   (Followers: 5)
The Cryosphere Discussions (TCD)     Open Access   (Followers: 4)
The Quarterly Journal of the Royal Meteorological Society     Hybrid Journal   (Followers: 27)
Theoretical and Applied Climatology     Hybrid Journal   (Followers: 12)
Tropical Cyclone Research and Review     Open Access   (Followers: 1)
Urban Climate     Hybrid Journal   (Followers: 4)
Weather     Hybrid Journal   (Followers: 19)
Weather and Climate Dynamics     Open Access  
Weather and Climate Extremes     Open Access   (Followers: 16)
Weather and Forecasting     Hybrid Journal   (Followers: 28)
Weatherwise     Hybrid Journal   (Followers: 4)
气候与环境研究     Full-text available via subscription   (Followers: 1)

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Journal Cover
Monthly Notices of the Royal Astronomical Society
Journal Prestige (SJR): 2.346
Citation Impact (citeScore): 4
Number of Followers: 14  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0035-8711 - ISSN (Online) 1365-2966
Published by Oxford University Press Homepage  [413 journals]
  • Interactions of a shock with a molecular cloud at various stages of its
           evolution due to thermal instability and gravity
    • Authors: Kupilas M; Wareing C, Pittard J, et al.
      Pages: 3137 - 3154
      Abstract: ABSTRACTUsing the adaptive mesh refinement code mg, we perform hydrodynamic simulations of the interaction of a shock with a molecular cloud evolving due to thermal instability (TI) and gravity. To explore the relative importance of these processes, three case studies are presented. The first follows the formation of a molecular cloud out of an initially quiescent atomic medium due to the effects of TI and gravity. The second case introduces a shock whilst the cloud is still in the warm atomic phase, and the third scenario introduces a shock once the molecular cloud has formed. The shocks accelerate the global collapse of the clouds with both experiencing local gravitational collapse prior to this. When the cloud is still atomic, the evolution is shock dominated and structures form due to dynamical instabilities within a radiatively cooled shell. While the transmitted shock can potentially trigger the TI, this is prevented as material is shocked multiple times on the order of a cloud-crushing time-scale. When the cloud is molecular, the post-shock flow is directed via the pre-existing structure through low-density regions in the inter-clump medium. The clumps are accelerated and deformed as the flow induces clump–clump collisions and mergers that collapse under gravity. For a limited period, both shocked cases show a mixture of Kolmogorov and Burgers turbulence-like velocity and logarithmic density power spectra, and strongly varying density spectra. The clouds presented in this work provide realistic conditions that will be used in future feedback studies.
      PubDate: Thu, 07 Jan 2021 00:00:00 GMT
      DOI: 10.1093/mnras/staa3889
      Issue No: Vol. 501, No. 3 (2021)
  • Erratum: Spectropolarimetric observations of the CIZA J2242.8+5301
           northern radio relic: no evidence of high-frequency steepening
    • Authors: Loi F; Murgia M, Vacca V, et al.
      Pages: 3183 - 3183
      Abstract: errata, addendapolarizationgalaxies: clusters: individual: CIZA J2242.8+5301radio continuum: general
      PubDate: Sat, 09 Jan 2021 00:00:00 GMT
      DOI: 10.1093/mnras/staa3947
      Issue No: Vol. 501, No. 3 (2021)
  • Shock-powered radio precursors of neutron star mergers from accelerating
           relativistic binary winds
    • Authors: Sridhar N; Zrake J, Metzger B, et al.
      Pages: 3184 - 3202
      Abstract: ABSTRACTDuring the final stages of a compact object merger, if at least one of the binary components is a magnetized neutron star (NS), then its orbital motion substantially expands the NS’s open magnetic flux – and hence increases its wind luminosity – relative to that of an isolated pulsar. As the binary orbit shrinks due to gravitational radiation, the power and speed of this binary-induced inspiral wind may (depending on pair loading) secularly increase, leading to self-interaction and internal shocks in the outflow beyond the binary orbit. The magnetized forward shock can generate coherent radio emission via the synchrotron maser process, resulting in an observable radio precursor to binary NS merger. We perform 1D relativistic hydrodynamical simulations of shock interaction in the accelerating binary NS wind, assuming that the inspiral wind efficiently converts its Poynting flux into bulk kinetic energy prior to the shock radius. This is combined with the shock maser spectrum from particle-in-cell simulations, to generate synthetic radio light curves. The precursor burst with a fluence of ∼1 Jy·ms at ∼GHz frequencies lasts ∼1–500 ms following the merger for a source at ∼3 Gpc (Bd/1012 G)8/9, where Bd is the dipole field strength of the more strongly magnetized star. Given an outflow geometry concentrated along the binary equatorial plane, the signal may be preferentially observable for high-inclination systems, that is, those least likely to produce a detectable gamma-ray burst.
      PubDate: Thu, 14 Jan 2021 00:00:00 GMT
      DOI: 10.1093/mnras/staa3794
      Issue No: Vol. 501, No. 3 (2021)
  • Measuring stellar atmosphere parameters using follow-up polarimetric
           microlensing observations
    • Authors: Khalouei E; Sajadian S, Rahvar S.
      Pages: 3203 - 3214
      Abstract: ABSTRACTWe present an analysis of potential follow-up polarimetric microlensing observations to study the stellar atmospheres of distant stars. First, we produce synthetic microlensing events using the Galactic model, stellar population and interstellar dust toward the Galactic bulge. We simulate the polarization microlensing light curves and pass them through the instrument specifications of the FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at the Very Large Telescope (VLT), and then analyse them. We find that the accuracy of the VLT allows us to constrain the atmospheres of cool red giant branch (RGB) stars. Assuming that about 3000 microlensing events are detected per year by the Optical Gravitational Lensing Experiment (OGLE) telescope, we expect to detect almost 20, 10, 8 and 5 polarization microlensing events for the following four criteria: being three consecutive polarimetric data points above the baseline with 1σ, 2σ, 3σ and 4σ, respectively, in the polarimetric light curves. We generalize the covariance matrix formulation and present the combination of polarimetric and icinformation that leads us to measure the scattering optical depth of the atmosphere and the inner radius of the stellar envelope of RGB stars. These two parameters could determine the dust opacity of the atmosphere of cool RGB source stars and the radius where dust can be formed.
      PubDate: Thu, 14 Jan 2021 00:00:00 GMT
      DOI: 10.1093/mnras/staa3492
      Issue No: Vol. 501, No. 3 (2021)
  • Properties of polarized synchrotron emission from fluctuation-dynamo
           action – I. Application to galaxy clusters
    • Authors: Sur S; Basu A, Subramanian K.
      Pages: 3332 - 3349
      Abstract: ABSTRACTUsing magnetohydrodynamic simulations of fluctuation dynamos, we perform broad-bandwidth synthetic observations to investigate the properties of polarized synchrotron emission and the role that Faraday rotation plays in inferring the polarized structures in the intracluster medium (ICM) of galaxy clusters. In the saturated state of the dynamo, we find a Faraday depth (FD) dispersion σFD ≈ 100 rad m−2, in agreement with observed values in the ICM. Remarkably, the FD power spectrum is qualitatively similar to M(k)/k, where M(k) is the magnetic spectrum and k the wavenumber. However, this similarity is broken at high k when FD is obtained by applying rotation measure (RM) synthesis to polarized emission from the ICM due to poor resolution and complexities of spectrum in FD space. Unlike the Gaussian probability distribution function (PDF) obtained for FD, the PDF of the synchrotron intensity is lognormal. A relatively large σFD in the ICM gives rise to strong frequency-dependent variations of the pixel-wise mean and peak polarized intensities at low frequencies ($\lesssim 1.5 \, {\rm GHz}$). The mean fractional polarization 〈p〉 obtained at the resolution of the simulations increases from <0.1 at 0.5 GHz to its intrinsic value of ∼0.3 at 6 GHz. Beam smoothing significantly affects the polarization properties below $\lesssim 1.5\, {\rm GHz}$, reducing 〈p〉 to ≲ 0.01 at 0.5 GHz. At frequencies $\gtrsim 5\, {\rm GHz}$, polarization remains largely unaffected, even when recovered using RM synthesis. Thus, our results underline the need for high-frequency ($\gtrsim 5\, {\rm GHz}$) observations with future radio telescopes to effectively probe the properties of polarized emission in the ICM.
      PubDate: Tue, 12 Jan 2021 00:00:00 GMT
      DOI: 10.1093/mnras/staa3767
      Issue No: Vol. 501, No. 3 (2021)
  • Erratum: The tale of the tail – disentangling the high transverse
           velocity stars in Gaia DR2
    • Authors: Amarante J; Smith M, Boeche C.
      Pages: 3392 - 3392
      Abstract: errata, addendaGalaxy: discGalaxy: haloGalaxy: kinematics and dynamics
      PubDate: Tue, 12 Jan 2021 00:00:00 GMT
      DOI: 10.1093/mnras/staa3847
      Issue No: Vol. 501, No. 3 (2021)
  • The physical properties and evolution of the interacting system
           AM 1204−292
    • Authors: Rosa D; Rodrigues I, Krabbe A, et al.
      Pages: 3750 - 3766
      Abstract: ABSTRACTWe investigate interaction effects in the stellar and gas kinematics, stellar population, and ionized gas properties of the interacting galaxy pair AM 1204−292,composed of NGC 4105 and NGC 4106. The data consist of long-slit spectra in the range 3000–7050 Å. The massive E3 galaxy NGC 4105 presents a flat stellar velocity profile, while the ionized gas is in strong rotation, suggesting an external origin. Its companion, NGC 4106, shows asymmetries in the radial velocity field, likely due to the interaction. The dynamics of the interacting pair were modelled using the P-Gadget3 treepm/sph code, from which we show that the system has just passed the first perigalacticum, which triggered an outbreak of star formation, currently at full maximum. We characterized the stellar population properties using the stellar population synthesis code starlight and, on average, both galaxies are predominantly composed of old stellar populations. NGC 4105 has a slightly negative age gradient, comparable with that of the most massive elliptical galaxies, but a steeper metallicity gradient. The SB0 galaxy NGC 4106 presents smaller radial variations in both age and metallicity in comparison with intermediate-mass early-type galaxies. These gradients have not been disturbed by interaction, since the star formation happened very recently and was not extensive in mass. Electron density estimates for the pair are systematically higher than those obtained in isolated galaxies. The central O/H abundances were obtained from photoionization models in combination with emission-line ratios, which resulted in 12 + log(O/H) = 9.03 ± 0.02 and 12 + log(O/H) = 8.69 ± 0.05 for NGC 4105 and NGC 4106, respectively.
      PubDate: Wed, 13 Jan 2021 00:00:00 GMT
      DOI: 10.1093/mnras/staa3850
      Issue No: Vol. 501, No. 3 (2021)
  • Retraction Notice: Revised instellation patterns for close-in exoplanets
    • Authors: Sadh M.
      Pages: 3846 - 3846
      Abstract: MNRAS is retracting the following article
      PubDate: Thu, 14 Jan 2021 00:00:00 GMT
      DOI: 10.1093/mnras/staa3930
      Issue No: Vol. 501, No. 3 (2021)
  • Feedback-limited accretion: variable luminosity from growing planets
    • Authors: Gárate M; Cuadra J, Montesinos M, et al.
      Pages: 3113 - 3121
      Abstract: ABSTRACTPlanets form in discs of gas and dust around stars, and continue to grow by accretion of disc material while available. Massive planets clear a gap in their protoplanetary disc, but can still accrete gas through a circumplanetary disc. For high enough accretion rates, the planet should be detectable at infrared wavelengths. As the energy of the gas accreted on to the planet is released, the planet surroundings heat up in a feedback process. We aim to test how this planet feedback affects the gas in the coorbital region and the accretion rate itself. We modified the 2D code FARGO-AD to include a prescription for the accretion and feedback luminosity of the planet and use it to model giant planets on 10 au circular and eccentric orbits around a solar mass star. We find that this feedback reduces but does not halt the accretion on to the planet, although this result might depend on the near-coincident radial ranges where both recipes are implemented. Our simulations also show that the planet heating gives the accretion rate a stochastic variability with an amplitude $\Delta \dot{M}_p \sim 0.1 \dot{M}_p$. A planet on an eccentric orbit (e = 0.1) presents a similar variability amplitude, but concentrated on a well-defined periodicity of half the orbital period and weaker broad-band noise, potentially allowing observations to discriminate between both cases. Finally, we find that the heating of the co-orbital region by the planet feedback alters the gas dynamics, reducing the difference between its orbital velocity and the Keplerian motion at the edge of the gap, which can have important consequences for the formation of dust rings.
      PubDate: Wed, 16 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3860
      Issue No: Vol. 501, No. 3 (2020)
  • The delay time distribution of supernovae from integral-field spectroscopy
           of nearby galaxies
    • Authors: Castrillo A; Ascasibar Y, Galbany L, et al.
      Pages: 3122 - 3136
      Abstract: ABSTRACTConstraining the delay time distribution (DTD) of different supernova (SN) types can shed light on the time-scales of galaxy chemical enrichment and feedback processes affecting galaxy dynamics, and SN progenitor properties. Here, we present an approach to recover SN DTDs based on integral-field spectroscopy (IFS) of their host galaxies. Using a statistical analysis of a sample of 116 SNe in 102 galaxies, we evaluate different DTD models for SN types Ia (73), II (28), and Ib/c (15). We find the best SN Ia DTD fit to be a power law with an exponent α = −1.1 ± 0.3 (50 per cent confidence interval (C.I.)), and a time delay (between star formation and the first SNe) $\Delta = 50^{+100}_{-35}~\mathrm{Myr}$ (50 per cent C.I.). For core collapse (CC) SNe, both of the Zapartas et al. DTD models for single and binary stellar evolution are consistent with our results. For SNe II and Ib/c, we find a correlation with a Gaussian DTD model with $\sigma = 82^{+129}_{-23}~\mathrm{Myr}$ and $\sigma = 56^{+141}_{-9}~\mathrm{Myr}$ (50 per cent C.I.), respectively. This analysis demonstrates that IFS opens a new way of studying SN DTD models in the local Universe.
      PubDate: Thu, 17 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3876
      Issue No: Vol. 501, No. 3 (2020)
  • Galactic and cosmological fast radio bursts as scaled-up solar radio
    • Authors: Wang F; Zhang G, Dai Z.
      Pages: 3155 - 3161
      Abstract: ABSTRACTFast radio bursts (FRBs) are bright milliseconds radio transients with large dispersion measures. Recently, FRB 200428 was detected in temporal coincidence with a hard X-ray flare from the Galactic magnetar SGR 1935+2154, which supports that at least some FRBs are from magnetar activity. Interestingly, a portion of X-ray flares from magnetar XTE J1810−197 and the Sun are also accompanied by radio bursts. Many features of Galactic FRB 200428 and cosmological FRBs resemble solar radio bursts. However, a common physical origin among FRBs, magnetar radio pulses, and solar radio bursts has not yet been established. Here, we report a universal correlation between X-ray luminosity and radio luminosity over 20 orders of magnitude among solar type III radio bursts, XTE J1810−197 and Galactic FRB 200428. This universal correlation reveals that the energetic electrons that produce the X-ray flares and those that cause radio emissions have a common origin, which can give stringent limits on the generation process of radio bursts. Moreover, we find similar occurrence frequency distributions of energy, duration, and waiting time for solar radio bursts, SGR 1935+2154 and repeating FRB 121102, which also support the tight correlation and the X-ray flares temporally associated with radio bursts. All of these distributions can be understood by avalanche models of self-organized criticality systems. The universal correlation and statistical similarities indicate that the Galactic FRB 200428 and FRBs seen at cosmological distances can be treated as scaled-up solar radio bursts.
      PubDate: Wed, 23 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3912
      Issue No: Vol. 501, No. 3 (2020)
  • Testing the intrinsic scatter of the asteroseismic scaling relations with
           Kepler red giants
    • Authors: Li Y; Bedding T, Stello D, et al.
      Pages: 3162 - 3172
      Abstract: ABSTRACTAsteroseismic scaling relations are often used to derive stellar masses and radii, particularly for stellar, exoplanet, and Galactic studies. It is therefore important that their precisions are known. Here we measure the intrinsic scatter of the underlying seismic scaling relations for Δν and νmax, using two sharp features that are formed in the H–R diagram (or related diagrams) by the red giant populations. These features are the edge near the zero-age core-helium-burning phase, and the strong clustering of stars at the so-called red giant branch bump. The broadening of those features is determined by factors including the intrinsic scatter of the scaling relations themselves, and therefore it is capable of imposing constraints on them. We modelled Kepler stars with a Galaxia synthetic population, upon which we applied the intrinsic scatter of the scaling relations to match the degree of sharpness seen in the observation. We found that the random errors from measuring Δν and νmax provide the dominating scatter that blurs the features. As a consequence, we conclude that the scaling relations have intrinsic scatter of $\sim 0.5$ (Δν), $\sim 1.1$ (νmax), $\sim 1.7$ (M), and $\sim 0.4{{\ \rm per\ cent}}$ (R), for the SYD pipeline measured Δν and νmax. This confirms that the scaling relations are very powerful tools. In addition, we show that standard evolution models fail to predict some of the structures in the observed population of both the HeB and RGB stars. Further stellar model improvements are needed to reproduce the exact distributions.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3932
      Issue No: Vol. 501, No. 3 (2020)
  • A two-component Comptonization model for the type-B QPO in MAXI
    • Authors: García F; Méndez M, Karpouzas K, et al.
      Pages: 3173 - 3182
      Abstract: ABSTRACTSpectral-timing analysis of the fast variability observed in X-rays is a powerful tool to study the physical and geometrical properties of the accretion/ejection flows in black hole (BH) binaries. The origin of type-B quasi-periodic oscillations (QPO), predominantly observed in BH candidates in the soft-intermediate state, has been linked to emission arising from the relativistic jet. In this state, the X-ray spectrum is characterized by a soft-thermal blackbody-like emission due to the accretion disc, an iron emission line (in the 6–7 keV range), and a power-law-like hard component due to inverse-Compton scattering of the soft-photon source by hot electrons in a corona or the relativistic jet itself. The spectral-timing properties of MAXI J1348−630 have been recently studied using observations obtained with the NICER observatory. The data show a strong type-B QPO at ∼4.5 Hz with increasing fractional rms amplitude with energy and positive lags with respect to a reference band at 2–2.5 keV. We use a variable-Comptonization model that assumes a sinusoidal coherent oscillation of the Comptonized X-ray flux and the physical parameters of the corona at the QPO frequency, to fit simultaneously the energy-dependent fractional rms amplitude and phase lags of this QPO. We show that two physically connected Comptonization regions can successfully explain the radiative properties of the QPO in the full 0.8–10 keV energy range.
      PubDate: Sat, 26 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3944
      Issue No: Vol. 501, No. 3 (2020)
  • emerge: empirical predictions of galaxy merger rates since z ∼ 6
    • Authors: O’Leary J; Moster B, Naab T, et al.
      Pages: 3215 - 3237
      Abstract: ABSTRACTWe explore the galaxy–galaxy merger rate with the empirical model for galaxy formation, emerge. On average, we find that between 2 per cent and 20 per cent of massive galaxies (log10(m*/M⊙) ≥ 10.3) will experience a major merger per Gyr. Our model predicts galaxy merger rates that do not scale as a power law with redshift when selected by descendant stellar mass, and exhibit a clear stellar mass and mass-ratio dependence. Specifically, major mergers are more frequent at high masses and at low redshift. We show mergers are significant for the stellar mass growth of galaxies log10(m*/M⊙) ≳ 11.0. For the most massive galaxies major mergers dominate the accreted mass fraction, contributing as much as 90 per cent of the total accreted stellar mass. We reinforce that these phenomena are a direct result of the stellar-to-halo mass relation, which results in massive galaxies having a higher likelihood of experiencing major mergers than low-mass galaxies. Our model produces a galaxy pair fraction consistent with recent observations, exhibiting a form best described by a power-law exponential function. Translating these pair fractions into merger rates results in an inaccurate prediction compared to the model intrinsic values when using published observation time-scales. We find the pair fraction can be well mapped to the intrinsic merger rate by adopting an observation time-scale that decreases linearly with redshift as Tobs = −0.36(1 + z) + 2.39 [Gyr], assuming all observed pairs merge by z = 0.
      PubDate: Thu, 17 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3746
      Issue No: Vol. 501, No. 3 (2020)
  • Rest-frame UV spectroscopy of extreme [O iii] emitters at 1.3 < z
           < 3.7: toward a high-redshift UV reference sample for JWST
    • Authors: Tang M; Stark D, Chevallard J, et al.
      Pages: 3238 - 3257
      Abstract: ABSTRACTDeep spectroscopy of galaxies in the reionization era has revealed intense C iii] and C iv line emission (equivalent width, EW >15–20 Å). In order to interpret the nebular emission emerging at z > 6, we have begun targeting rest-frame ultraviolet (UV) emission lines in galaxies with large specific star formation rates (sSFRs) at 1.3 < z < 3.7. We find that C iii] reaches the EWs seen at z > 6 only in large sSFR galaxies with [O iii]+Hβ EW >1500 Å. In contrast to previous studies, we find that many galaxies with intense [O iii] have weak C iii] emission (EW = 5–8 Å), suggesting that the radiation field associated with young stellar populations is not sufficient to power strong C iii]. Photoionization models demonstrate that the spread in C iii] among systems with large sSFRs ([O iii]+Hβ EW >1500 Å) is driven by variations in metallicity, a result of the extreme sensitivity of C iii] to electron temperature. We find that the strong C iii] emission seen at z > 6 (EW >15 Å) requires metal-poor gas (≃ 0.1 Z⊙), whereas the weaker C iii] emission in our sample tends to be found at moderate metallicities (≃ 0.3 Z⊙). The luminosity distribution of the C iii] emitters in our z ≃ 1–3 sample presents a consistent picture, with stronger emission generally linked to low-luminosity systems (MUV > −19.5) where low metallicities are more likely. We quantify the fraction of strong C iii] and C iv emitters at z ≃ 1–3, providing a baseline for comparison against z > 6 samples. We suggest that the first UV line detections at z > 6 can be explained if a significant fraction of the early galaxy population is found at large sSFR (>200 Gyr−1) and low metallicity (< 0.1 Z⊙).
      PubDate: Sat, 07 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3454
      Issue No: Vol. 501, No. 3 (2020)
  • SSSpaNG! stellar spectra as sparse, data-driven, non-Gaussian processes
    • Authors: Feeney S; Wandelt B, Ness M.
      Pages: 3258 - 3271
      Abstract: ABSTRACTUpcoming million-star spectroscopic surveys have the potential to revolutionize our view of the formation and chemical evolution of the Milky Way. Realizing this potential requires automated approaches to optimize estimates of stellar properties, such as chemical element abundances, from the spectra. The sheer volume and quality of the observations strongly motivate that these approaches should be driven by the data. With this in mind, we introduce SSSpaNG: a data-driven non-Gaussian Process model of stellar spectra. We demonstrate the capabilities of SSSpaNG using a sample of APOGEE red clump stars, whose model parameters we infer using Gibbs sampling. By pooling information between stars to infer their covariance, we permit clear identification of the correlations between spectral pixels. Harnessing this correlation structure, we infer the true spectrum of each red clump star, inpainting missing regions and denoising by a factor of at least two for stars with signal-to-noise ratios of ∼20. As we marginalize over the covariance matrix of the spectra, the effective prior on these true spectra is non-Gaussian and sparsifying, favouring typically small but occasionally large excursions from the mean. The high-fidelity inferred spectra produced with our approach will enable improved chemical elemental abundance estimates for individual stars. Our model also allows us to quantify the information gained by observing portions of a star’s spectrum, and thereby define the most mutually informative spectral regions. Using 25 windows centred on elemental absorption lines, we demonstrate that the iron-peak and alpha-process elements are particularly mutually informative for these spectra and that the majority of information about a target window is contained in the 10-or-so most informative windows. Such mutual information estimates have the potential to inform models of nucleosynthetic yields and the design of future observations. Our code is made publicly available at https://github.com/sfeeney/ddspectra.
      PubDate: Wed, 18 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3586
      Issue No: Vol. 501, No. 3 (2020)
  • fink, a new generation of broker for the LSST community
    • Authors: Möller A; Peloton J, Ishida E, et al.
      Pages: 3272 - 3288
      Abstract: ABSTRACTfink is a broker designed to enable science with large time-domain alert streams such as the one from the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). It exhibits traditional astronomy broker features such as automatized ingestion, annotation, selection, and redistribution of promising alerts for transient science. It is also designed to go beyond traditional broker features by providing real-time transient classification that is continuously improved by using state-of-the-art deep learning and adaptive learning techniques. These evolving added values will enable more accurate scientific output from LSST photometric data for diverse science cases while also leading to a higher incidence of new discoveries which shall accompany the evolution of the survey. In this paper, we introduce fink, its science motivation, architecture, and current status including first science verification cases using the Zwicky Transient Facility alert stream.
      PubDate: Thu, 19 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3602
      Issue No: Vol. 501, No. 3 (2020)
  • First Light And Reionization Epoch Simulations (FLARES) -- II: The
           photometric properties of high-redshift galaxies
    • Authors: Vijayan A; Lovell C, Wilkins S, et al.
      Pages: 3289 - 3308
      Abstract: ABSTRACTWe present the photometric properties of galaxies in the First Light And Reionization Epoch Simulations (FLARES). The simulations trace the evolution of galaxies in a range of overdensities through the epoch of reionization. With a novel weighting scheme, we combine these overdensities, extending significantly the dynamic range of observed composite distribution functions compared to periodic simulation boxes. FLARES predicts a significantly larger number of intrinsically bright galaxies, which can be explained through a simple model linking dust attenuation to the metal content of the interstellar medium, using a line-of-sight extinction model. With this model, we present the photometric properties of the FLARES galaxies for z ∈ [5, 10]. We show that the ultraviolet (UV) luminosity function (LF) matches the observations at all redshifts. The function is fitted by Schechter and double power-law forms, with the latter being favoured at these redshifts by the FLARES composite UV LF. We also present predictions for the UV-continuum slope as well as the attenuation in the UV. The impact of environment on the UV LF is also explored, with the brightest galaxies forming in the densest environments. We then present the line luminosity and equivalent widths of some prominent nebular emission lines arising from the galaxies, finding rough agreement with available observations. We also look at the relative contribution of obscured and unobscured star formation, finding comparable contributions at these redshifts.
      PubDate: Mon, 30 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3715
      Issue No: Vol. 501, No. 3 (2020)
  • The clustering of DESI-like luminous red galaxies using photometric
    • Authors: Zhou R; Newman J, Mao Y, et al.
      Pages: 3309 - 3331
      Abstract: ABSTRACTWe present measurements of the redshift-dependent clustering of a DESI-like luminous red galaxy (LRG) sample selected from the Legacy Survey imaging data set, and use the halo occupation distribution (HOD) framework to fit the clustering signal. The photometric LRG sample in this study contains 2.7 million objects over the redshift range of 0.4 < z < 0.9 over 5655 deg2. We have developed new photometric redshift (photo-z) estimates using the Legacy Survey DECam and WISE photometry, with σNMAD = 0.02 precision for LRGs. We compute the projected correlation function using new methods that maximize signal-to-noise ratio while incorporating redshift uncertainties. We present a novel algorithm for dividing irregular survey geometries into equal-area patches for jackknife resampling. For a five-parameter HOD model fit using the MultiDark halo catalogue, we find that there is little evolution in HOD parameters except at the highest redshifts. The inferred large-scale structure bias is largely consistent with constant clustering amplitude over time. In an appendix, we explore limitations of Markov chain Monte Carlo fitting using stochastic likelihood estimates resulting from applying HOD methods to N-body catalogues, and present a new technique for finding best-fitting parameters in this situation. Accompanying this paper, we have released the Photometric Redshifts for the Legacy Surveys catalogue of photo-z’s obtained by applying the methods used in this work to the full Legacy Survey Data Release 8 data set. This catalogue provides accurate photometric redshifts for objects with z < 21 over more than 16 000 deg2 of sky.
      PubDate: Fri, 04 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3764
      Issue No: Vol. 501, No. 3 (2020)
  • The correlation between impact crater ages and chronostratigraphic
           boundary dates
    • Authors: Firestone R.
      Pages: 3350 - 3363
      Abstract: ABSTRACTThe accurately measured ages of 89 large impact craters and layers were compared with the boundary dates for periods, epochs, and ages of the geological time-scale by a weighted least-squares fit. They are highly correlated with a χ2/f = 0.63. A Monte Carlo simulation of randomly chosen crater ages gives a >99.8 per cent probability that this result is not random. No craters are found in the oceans or, until recently, in ice which collectively cover 80 per cent of Earth’s surface indicating that far more impacts have occurred than are known. Multiple impacts cluster near the times of boundary dates so, based on the observed cluster sizes assuming a binomial distribution, it was determined that the average cluster multiplicity is five. Comparison of the impact ages with the dates of the great extinctions revealed a strong correlation with χ2/f = 0.36 and a multiplicity of 8–9 impacts. It is shown that volcanism, although correlated with boundary dates, is a continuous process unrelated to sudden extinctions. During the past 125 Ma, the rate of global change and the impact rate have increased dramatically as the Earth passes near the OB star association. Multiple impacts 12.9 ka ago ended the Pleistocene epoch at the onset of the Younger Dryas (YD) causing worldwide extinctions. The date and extent of the YD impact may be consistent with a 62 Ma cycle of major impact events. During the Holocene 20 crater, airburst and impact tsunami chevron ages correspond to dates of global cooling with a χ2/f = 0.75 and >99 per cent probability. Future impacts could reverse global warming or even induce next ice age.
      PubDate: Fri, 18 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3790
      Issue No: Vol. 501, No. 3 (2020)
  • Angular power spectrum of supernova remnants: effects of structure,
           geometry, and diffuse foreground
    • Authors: Choudhuri S; Saha P, Roy N, et al.
      Pages: 3364 - 3370
      Abstract: ABSTRACTThe study of the intensity fluctuation power spectrum of individual supernova remnants (SNRs) can reveal the structures present at sub-pc scales, and also constrain the physical process that generates those structures. There are various effects, such as the remnant shell thickness, projection of a three-dimensional structure on to a two-dimensional observational plane, and the presence of diffuse ‘foreground’ emission, which causes the observed power spectrum to deviate from the intrinsic power spectrum of the fluctuations. Here, we report results from a systematic study of these effects, using direct numerical simulations, in the measured power spectrum. For an input power-law power spectrum, independent of the power-law index, we see a break in the observed power law at a scale which depends on the shell thickness of a shell-type SNR, and the three-dimensional turbulence changes to two-dimensional turbulence beyond that scale. We also report how the estimated power spectrum is expected to deviate from the intrinsic SNR power spectrum in the presence of additional diffuse Galactic synchrotron emission (DGSE) around the remnant shell. For a reasonable choice of the parameters, if the intrinsic SNR power spectrum is shallower than the DGSE power spectrum, the SNR contribution dominates at small angular scales of the estimated power spectra. On the other hand, if the SNR power spectrum is relatively steeper, the original power spectra is recovered only over a small window of angular scales. This study shows how detailed modelling may be used to infer the true power spectrum from the observed SNR intensity fluctuations power spectrum, which in turn can be used to constrain the nature of the turbulence that gives rise to these small-scale structures.
      PubDate: Wed, 09 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3798
      Issue No: Vol. 501, No. 3 (2020)
  • A simple, heuristic derivation of the Balescu–Lenard kinetic
           equation for stellar systems
    • Authors: Hamilton C.
      Pages: 3371 - 3377
      Abstract: ABSTRACTThe unshielded nature of gravity means that stellar systems are inherently inhomogeneous. As a result, stars do not move in straight lines. This obvious fact severely complicates the kinetic theory of stellar systems because position and velocity turn out to be poor coordinates with which to describe stellar orbits – instead, one must use angle-action variables. Moreover, the slow relaxation of star clusters and galaxies can be enhanced or suppressed by collective interactions (‘polarization’ effects) involving many stars simultaneously. These collective effects are also present in plasmas; in that case they are accounted for by the Balescu–Lenard (BL) equation, which is a kinetic equation in velocity space. Recently, several authors have shown how to account for both inhomogeneity and collective effects in the kinetic theory of stellar systems by deriving an angle-action generalization of the BL equation. Unfortunately their derivations are long and complicated, involving multiple coordinate transforms, contour integrals in the complex plane, and so on. On the other hand, Rostoker’s superposition principle allows one to pretend that a long-range interacting N-body system, such as a plasma or star cluster, consists merely of uncorrelated particles that are ‘dressed’ by polarization clouds. In this paper, we use Rostoker’s principle to provide a simple, intuitive derivation of the BL equation for stellar systems which is much shorter than others in the literature. It also allows us to straightforwardly connect the BL picture of self-gravitating kinetics to the classical ‘two-body relaxation’ theory of uncorrelated flybys pioneered by Chandrasekhar.
      PubDate: Thu, 10 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3807
      Issue No: Vol. 501, No. 3 (2020)
  • Demonstrating the Tapered Gridded Estimator (TGE) for the cosmological
           H i 21-cm power spectrum using 150-MHz GMRT observations
    • Authors: Pal S; Bharadwaj S, Ghosh A, et al.
      Pages: 3378 - 3391
      Abstract: ABSTRACTWe apply the Tapered Gridded Estimator for estimating the cosmological 21-cm power spectrum from $150\hbox{-}{\rm MHz}$ GMRT observations, which corresponds to the neutral hydrogen (H i) at redshift z = 8.28. Here, TGE is used to measure the multifrequency angular power spectrum (MAPS) Cℓ(Δν) first, from which we estimate the 21-cm power spectrum P(k⊥, k∥). The data here are much too small for a detection, and the aim is to demonstrate the capabilities of the estimator. We find that the estimated power spectrum is consistent with the expected foreground and noise behaviour. This demonstrates that this estimator correctly estimates the noise bias and subtracts this out to yield an unbiased estimate of the power spectrum. More than $47{{\ \rm per\ cent}}$ of the frequency channels had to be discarded from the data owing to radio–frequency interference, however, the estimated power spectrum does not show any artefacts due to missing channels. Finally, we show that it is possible to suppress the foreground contribution by tapering the sky response at large angular separations from the phase centre. We combine the k modes within a rectangular region in the ‘EoR window’ to obtain the spherically binned averaged dimensionless power spectra Δ2(k) along with the statistical error σ associated with the measured Δ2(k). The lowest k-bin yields $\Delta ^{2}(k)=(61.47)^{2}\, {\rm K}^{2}$ at $k=1.59\, \textrm {Mpc}^{-1}$, with $\sigma =(27.40)^{2} \, {\rm K}^{2}$. We obtain a $2 \, \sigma$ upper limit of $(72.66)^{2}\, \textrm {K}^{2}$ on the mean squared H i 21-cm brightness temperature fluctuations at $k=1.59\, \textrm {Mpc}^{-1}$.
      PubDate: Sat, 12 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3831
      Issue No: Vol. 501, No. 3 (2020)
  • Spectral and polarization properties of black hole accretion disc
           emission: including absorption effects
    • Authors: Taverna R; Marra L, Bianchi S, et al.
      Pages: 3393 - 3405
      Abstract: ABSTRACTThe study of radiation emitted from black hole (BH) accretion discs represents a crucial way to understand the main physical properties of these sources, and in particular the BH spin. Beside spectral analysis, polarimetry is becoming more and more important, motivated by the development of new techniques which will soon allow to perform measurements also in the X- and γ-rays. Photons emitted from BH accretion discs in the soft state are indeed expected to be polarized, with an energy dependence which can provide an estimate of the BH spin. Calculations performed so far, however, considered scattering as the only process to determine the polarization state of the emitted radiation, implicitly assuming that the temperatures involved are such that material in the disc is entirely ionized. In this work, we generalize the problem by calculating the ionization structure of a surface layer of the disc with the public code cloudy, and then by determining the polarization properties of the emerging radiation using the Monte Carlo code stokes. This allows us to account for absorption effects alongside scattering ones. We show that including absorption can deeply modify the polarization properties of the emerging radiation with respect to what is obtained in the pure-scattering limit. As a general rule, we find that the polarization degree is larger when absorption is more important, which occurs, for example, for low accretion rates and/or spins when the ionization of the matter in the innermost accretion disc regions is far from complete.
      PubDate: Wed, 16 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3859
      Issue No: Vol. 501, No. 3 (2020)
  • Using optical spectroscopy to map the geometry and structure of the
           irradiated accretion discs in low-mass X-ray binaries: the pilot study of
           MAXI J0637–430
    • Authors: Tetarenko B; Shaw A, Manrow E, et al.
      Pages: 3406 - 3420
      Abstract: ABSTRACTThe recurring transient outbursts in low-mass X-ray binaries (LMXBs) provide us with strong test-beds for constraining the poorly understood accretion process. While impossible to image directly, phase-resolved spectroscopy can provide a powerful diagnostic to study their highly complex, time-dependent accretion discs. We present an 8-month long multiwavelength (UV, optical, X-ray) monitoring campaign of the new candidate black hole LMXB MAXI J0637–430 throughout its 2019/2020 outburst, using the Neil Gehrels Swift Observatory, as well as three quasi-simultaneous epochs of Gemini/GMOS optical spectroscopy. We find evidence for the existence of a correlation between the X-ray irradiation heating the accretion disc and the evolution of the He ii 4686 Å emission line profiles detected in the optical spectra. Our results demonstrate a connection between the line emitting regions and physical properties of the X-ray irradiation heating the discs during outburst cycles of LMXBs. Further, we are able to show that changes in the physical properties of the irradiation heating the disc in outburst can be imprinted within the H/He emission line profiles themselves in these systems.
      PubDate: Thu, 24 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3861
      Issue No: Vol. 501, No. 3 (2020)
  • Hints for possible low redshift oscillation around the best-fitting ΛCDM
           model in the expansion history of the Universe
    • Authors: Kazantzidis L; Koo H, Nesseris S, et al.
      Pages: 3421 - 3426
      Abstract: ABSTRACTWe search for possible deviations from the expectations of the concordance ΛCDM model in the expansion history of the Universe by analysing the Pantheon Type Ia Supernovae (SnIa) compilation along with its Monte Carlo simulations using redshift binning. We demonstrate that the redshift binned best-fitting ΛCDM matter density parameter Ω0m and the best-fitting effective absolute magnitude $\cal M$ oscillate about their full data set best-fitting values with considerably large amplitudes. Using the full covariance matrix of the data taking into account systematic and statistical errors, we show that at the redshifts below z ≈ 0.5 such oscillations can only occur in 4 to 5 ${{\ \rm per\ cent}}$ of the Monte Carlo simulations. While statistical fluctuations can be responsible for this apparent oscillation, we might have observed a hint for some behaviour beyond the expectations of the concordance model or a possible additional systematic in the data. If this apparent oscillation is not due to statistical or systematic effects, it could be due to either the presence of coherent inhomogeneities at low z or due to oscillations of a quintessence scalar field.
      PubDate: Thu, 17 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3866
      Issue No: Vol. 501, No. 3 (2020)
  • High-resolution observations of molecular emission lines toward the CI Tau
           proto-planetary disc: planet-carved gaps or shadowing'
    • Authors: Rosotti G; Ilee J, Facchini S, et al.
      Pages: 3427 - 3442
      Abstract: ABSTRACTRecent observations have revealed that most proto-planetary discs show a pattern of bright rings and dark gaps. However, most of the high-resolution observations have focused only on the continuum emission. In this paper, we present high-resolution ALMA band 7 (0.89 mm) observations of the disc around the star CI Tau in the 12CO & 13CO J = 3–2 and CS J = 7–6 emission lines. Our recent work demonstrated that the disc around CI Tau contains three gaps and rings in continuum emission, and we look for their counterparts in the gas emission. While we find no counterpart of the third gap and ring in 13CO, the disc has a gap in emission at the location of the second continuum ring (rather than gap). We demonstrate that this is mostly an artefact of the continuum subtraction, although a residual gap still remains after accounting for this effect. Through radiative transfer modelling, we propose this is due to the inner disc shadowing the outer parts of the disc and making them colder. This raises a note of caution in mapping high-resolution gas emission lines observations to the gas surface density – while possible, this needs to be done carefully. In contrast to 13CO, CS emission shows instead a ring morphology, most likely due to chemical effects. Finally, we note that 12CO is heavily absorbed by the foreground preventing any morphological study using this line.
      PubDate: Thu, 17 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3869
      Issue No: Vol. 501, No. 3 (2020)
  • DO-CRIME: dynamic on-sky covariance random interaction matrix evaluation,
           a novel method for calibrating adaptive optics systems
    • Authors: Lai O; Chun M, Dungee R, et al.
      Pages: 3443 - 3456
      Abstract: ABSTRACTAdaptive optics (AO) systems require a calibration procedure to operate, whether in closed loop or even more importantly in forward control. This calibration usually takes the form of an interaction matrix and is a measure of the response on the wavefront sensor (WFS) to wavefront corrector stimulus. If this matrix is sufficiently well conditioned, it can be inverted to produce a control matrix, which allows to compute the optimal commands to apply to the wavefront corrector for a given WFS measurement vector. Interaction matrices are usually measured by means of an artificial source at the entrance focus of the AO system; however, adaptive secondary mirrors (ASMs) on Cassegrain telescopes offer no such focus and the measurement of their interaction matrices becomes more challenging and needs to be done on-sky using a natural star. The most common method is to generate a theoretical or simulated interaction matrix and adjust it parametrically (e.g. magnification, rotation) using on-sky measurements. We propose a novel method of measuring on-sky interaction matrices ab initio from the telemetry stream of the AO system using random patterns on the deformable mirror with diagonal commands covariance matrices. The approach, being developed for the ASM upgrade for the imaka wide-field AO system on the UH2.2m telescope project, is shown to work on-sky using the current imaka testbed.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3874
      Issue No: Vol. 501, No. 3 (2020)
  • A machine-learning approach for classifying low-mass X-ray binaries based
           on their compact object nature
    • Authors: Pattnaik R; Sharma K, Alabarta K, et al.
      Pages: 3457 - 3471
      Abstract: ABSTRACTLow-mass X-ray binaries (LMXBs) are binary systems where one of the components is either a black hole or a neutron star and the other is a less massive star. It is challenging to unambiguously determine whether an LMXB hosts a black hole or a neutron star. In the last few decades, multiple observational works have tried, with different levels of success, to address this problem. In this paper, we explore the use of machine learning to tackle this observational challenge. We train a random forest classifier to identify the type of compact object using the energy spectrum in the energy range 5–25 keV obtained from the Rossi X-ray Timing Explorer archive. We report an average accuracy of 87 ± 13 per cent in classifying the spectra of LMXB sources. We further use the trained model for predicting the classes for LMXB systems with unknown or ambiguous classification. With the ever-increasing volume of astronomical data in the X-ray domain from present and upcoming missions (e.g. Swift, XMM–Newton, XARM, Athena, and NICER), such methods can be extremely useful for faster and robust classification of X-ray sources and can also be deployed as part of the data reduction pipeline.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3899
      Issue No: Vol. 501, No. 3 (2020)
  • Gibbs point process model for young star clusters in M33
    • Authors: Li D; Barmby P.
      Pages: 3472 - 3489
      Abstract: ABSTRACTWe demonstrate the power of Gibbs point process models from the spatial statistics literature when applied to studies of resolved galaxies. We conduct a rigorous analysis of the spatial distributions of objects in the star formation complexes of M33, including giant molecular clouds (GMCs) and young stellar cluster candidates (YSCCs). We choose a hierarchical model structure from GMCs to YSCCs based on the natural formation hierarchy between them. This approach circumvents the limitations of the empirical two-point correlation function analysis by naturally accounting for the inhomogeneity present in the distribution of YSCCs. We also investigate the effects of GMCs’ properties on their spatial distributions. We confirm that the distribution of GMCs and YSCCs are highly correlated. We found that the spatial distributions of YSCCs reaches a peak of clustering pattern at ∼250 pc scale compared to a Poisson process. This clustering mainly occurs in regions where the galactocentric distance ≳4.5 kpc. Furthermore, the galactocentric distance of GMCs and their mass have strong positive effects on the correlation strength between GMCs and YSCCs. We outline some possible implications of these findings for our understanding of the cluster formation process.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3908
      Issue No: Vol. 501, No. 3 (2020)
  • Clustering in the simulated H α galaxy redshift survey from Nancy Grace
           Roman Space Telescope
    • Authors: Zhai Z; Chuang C, Wang Y, et al.
      Pages: 3490 - 3501
      Abstract: ABSTRACTWe present a realistic 2000 deg2 H α galaxy mock catalogue with 1 < z < 2 for the Nancy Grace Roman Space Telescope (Roman) galaxy redshift survey, the High Latitude Spectroscopic Survey (HLSS), created using Galacticus, a semi-analytical galaxy formation model, and high-resolution cosmological N-body simulations. Galaxy clustering can probe dark energy and test gravity via baryon acoustic oscillation (BAO) and redshift space distortion (RSD) measurements. Using our realistic mock as the simulated Roman HLSS data, and a covariance matrix computed using a large set of approximate mocks created using ezmock, we investigate the expected precision and accuracy of the BAO and RSD measurements using the same analysis techniques used in analysing real data. We find that the Roman H α galaxy survey alone can measure the angular diameter distance with 2 per cent uncertainty, the Hubble parameter with 3–6 per cent uncertainty, and the linear growth parameter with 7 per cent uncertainty, in each of four redshift bins. Our realistic forecast illustrates the power of the Roman galaxy survey in probing the nature of dark energy and testing gravity.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3911
      Issue No: Vol. 501, No. 3 (2020)
  • Proplyds in the flame nebula NGC 2024
    • Authors: Haworth T; Kim J, Winter A, et al.
      Pages: 3502 - 3514
      Abstract: ABSTRACTA recent survey of the inner 0.35 × 0.35 pc of the NGC 2024 star-forming region revealed two distinct millimetre continuum disc populations that appear to be spatially segregated by the boundary of a dense cloud. The eastern (and more embedded) population is ∼0.2–0.5 Myr old, with an ALMA mm continuum disc detection rate of about $45\,$ per cent. However, this drops to only $\sim 15\,$ per cent in the 1-Myr western population. When these distinct populations were presented, it was suggested that the two main UV sources, IRS 1 (a B0.5V star in the western region) and IRS 2b (an O8V star in the eastern region, but embedded) have both been evaporating the discs in the depleted western population. In this paper, we report the firm discovery in archival HST data of four proplyds and four further candidate proplyds in NGC 2024, confirming that external photoevaporation of discs is occurring. However, the locations of these proplyds changes the picture. Only three of them are in the depleted western population and their evaporation is dominated by IRS 1, with no obvious impact from IRS 2b. The other five proplyds are in the younger eastern region and being evaporated by IRS 2b. We propose that both populations are subject to significant external photoevaporation, which happens throughout the region wherever discs are not sufficiently shielded by the interstellar medium. The external photoevaporation and severe depletion of mm grains in the 0.2–0.5 Myr eastern part of NGC 2024 would be in competition even with very early planet formation.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3918
      Issue No: Vol. 501, No. 3 (2020)
  • Improving sampling and calibration of gamma-ray bursts as distance
    • Authors: Montiel A; Cabrera J, Hidalgo J.
      Pages: 3515 - 3526
      Abstract: ABSTRACTWe present a sample of 74 gamma-ray bursts (GRBs) from the Fermi-GBM catalogue for which we compute the distance moduli and use them to constrain effective dark energy models. To overcome the circularity problem affecting GRBs as distance indicators, we calibrate the Amati relation of our sample with a cosmology-independent technique. Specifically, we use the latest observational Hubble parameter data, including associated systematics, to approximate the cosmic expansion through a Bezier parametric curve. We subsequently obtain the distance moduli of the GRBs and include the data in a suite of recent cosmological observations of the expansion history (Planck Compressed 2018, 2012 BOSS release of BAO data, and Pantheon SN Ia), to compute Bayesian posterior constraints for the standard cosmological model Lambda cold dark matter (ΛCDM), as well as ωCDM, and the CPL parametrization. Throughout the analysis, we strive to keep under control the error propagation and limit our GRB sample to avoid observational bias. As a result, we find no evidence in favour of the alternatives to ΛCDM model. The latter agrees very well with our calibrated sample of GRBs and presently available luminosity distance probes.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3926
      Issue No: Vol. 501, No. 3 (2020)
  • Thick disc molecular gas fraction in NGC 6946
    • Authors: Patra N.
      Pages: 3527 - 3539
      Abstract: ABSTRACTSeveral recent studies reinforce the existence of a thick molecular disc in galaxies along with the dynamically cold thin disc. Assuming a two-component molecular disc, we model the disc of NGC 6946 as a four-component system consisting of stars, H i, thin disc molecular gas, and thick disc molecular gas in vertical hydrostatic equilibrium. Following, we set up the joint Poisson–Boltzmann equation of hydrostatic equilibrium and solve it numerically to obtain a three-dimensional density distribution of different baryonic components. Using the density solutions and the observed rotation curve, we further build a three-dimensional dynamical model of the molecular disc and consecutively produce simulated CO spectral cubes and spectral width profiles. We find that the simulated spectral width profiles distinguishably differ for different assumed thick disc molecular gas fractions. Several CO spectral width profiles are then produced for different assumed thick disc molecular gas fractions and compared with the observed one to obtain the best fit thick disc molecular gas fraction profile. We find that the thick disc molecular gas fraction in NGC 6946 largely remains constant across its molecular disc with a mean value of 0.70 ± 0.09. We also estimate the amount of extra-planar molecular gas in NGC 6946. We find $\sim 50{{\ \rm per\ cent}}$ of the total molecular gas is extra-planar at the central region, whereas this fraction reduces to ∼15 per cent at the edge of the molecular disc. With our method, for the first time, we estimate the thick disc molecular gas fraction as a function of radius in an external galaxy with sub-kpc resolution.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3929
      Issue No: Vol. 501, No. 3 (2020)
  • Evolution of gas disc–embedded intermediate mass ratio inspirals in
           the LISA band
    • Authors: Derdzinski A; D’Orazio D, Duffell P, et al.
      Pages: 3540 - 3557
      Abstract: ABSTRACTAmong the potential milliHz gravitational wave (GW) sources for the upcoming space-based interferometer LISA are extreme- or intermediate-mass ratio inspirals (EMRI/IMRIs). These events involve the coalescence of supermassive black holes in the mass range 105M⊙ ≲ M ≲ 107M⊙ with companion BHs of much lower masses. A subset of E/IMRIs are expected to occur in the accretion discs of active galactic nuclei (AGNs), where torques exerted by the disc can interfere with the inspiral and cause a phase shift in the GW waveform. Here we use a suite of 2D hydrodynamical simulations with the moving-mesh code disco to present a systematic study of disc torques. We measure torques on an inspiralling BH and compute the corresponding waveform deviations as a function of the binary mass ratio q ≡ M2/M1, the disc viscosity (α), and gas temperature (or equivalently Mach number; $\mathcal {M}$). We find that the absolute value of the gas torques is within an order of magnitude of previously determined planetary migration torques, but their precise value and sign depends non-trivially on the combination of these parameters. The gas imprint is detectable by LISA for binaries embedded in AGN discs with surface densities above $\Sigma _0\ge 10^{4-6} \rm \, g cm^{-2}$, depending on q, α, and $\mathcal {M}$. Deviations are most pronounced in discs with higher viscosities, and for E/IMRIs detected at frequencies where LISA is most sensitive. Torques in colder discs exhibit a noticeable dependence on the GW-driven inspiral rate as well as strong fluctuations at late stages of the inspiral. Our results further suggest that LISA may be able to place constraints on AGN disc parameters and the physics of disc–satellite interaction.
      PubDate: Tue, 29 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3976
      Issue No: Vol. 501, No. 3 (2020)
  • Baryonic effects on the detectability of annihilation radiation from dark
           matter subhaloes around the Milky Way
    • Authors: Grand R; White S.
      Pages: 3558 - 3567
      Abstract: ABSTRACTWe use six, high-resolution Λ-cold dark matter (ΛCDM) simulations of galaxy formation to study how emission from dark matter annihilation is affected by baryonic processes. These simulations produce isolated, disc-dominated galaxies with structure, stellar populations, and stellar and halo masses comparable to those of the Milky Way. They resolve dark matter structures with mass above ∼106  $\rm M_{\odot }$ and are each available in both full-physics and dark-matter-only versions. In the full-physics case, formation of the stellar galaxy enhances annihilation radiation from the dominant smooth component of the galactic halo by a factor of 3, and its central concentration increases substantially. In contrast, subhalo fluxes are reduced by almost an order of magnitude, partly because of changes in internal structure, partly because of increased tidal effects; they drop relative to the flux from the smooth halo by 1.5 orders of magnitude. The expected flux from the brightest Milky Way subhalo is four orders of magnitude below that from the smooth halo, making it very unlikely that any subhalo will be detected before robust detection of the inner Galaxy. We use recent simulations of halo structure across the full ΛCDM mass range to extrapolate to the smallest (Earth-mass) subhaloes, concluding, in contrast to earlier work, that the total annihilation flux from Milky Way subhaloes will be less than that from the smooth halo, as viewed both from the Sun and by a distant observer. Fermi-Large Area Telescope may marginally resolve annihilation radiation from the very brightest subhaloes, which, typically, will contain stars.
      PubDate: Sat, 26 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3993
      Issue No: Vol. 501, No. 3 (2020)
  • MEGARA-GTC stellar spectral library – II. MEGASTAR first release
    • Authors: Carrasco E; Mollá M, García-Vargas M, et al.
      Pages: 3568 - 3581
      Abstract: ABSTRACTMEGARA is an optical integral field and multi-object fibre-based spectrograph for the 10.4 m Gran Telescopio CANARIAS that offers medium-to-high spectral resolutions (FWHM) of R ≃ 6000, 12 000, 20 000. Commissioned at the telescope in 2017, it started operation as a common-user instrument in 2018. We are creating an instrument-oriented empirical spectral library from MEGARA-GTC stars observations, MEGASTAR, crucial for the correct interpretation of MEGARA data. This piece of work describes the content of the first release of MEGASTAR, formed by the spectra of 414 stars observed with R ≃ 20 000 in the spectral intervals 6420–6790 Å and 8370–8885 Å, and obtained with a continuum average signal-to-noise ratio around 260. We describe the release sample, the observations, the data reduction procedure and the MEGASTAR data base. Additionally, we include in Appendix AAppendix A an atlas with the complete set of 838 spectra of this first release of the MEGASTAR catalogue.
      PubDate: Tue, 01 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3704
      Issue No: Vol. 501, No. 3 (2020)
  • Detailed studies of IPHAS sources – I. The disrupted late bipolar
           IPHASX J193718.6+202102
    • Authors: Sabin L; Guerrero M, Zavala S, et al.
      Pages: 3582 - 3593
      Abstract: ABSTRACTWe present a detailed analysis of the new planetary nebula (PN) IPHASX J193718.6+202102 using deep imaging and intermediate- and high-resolution spectroscopy that are interpreted through morpho-kinematic and photoionization modelling. The physical structure of the nebula consists of a fragmented torus and an extremely faint orthogonal bipolar outflow, contrary to the pinched waist PN morphology suggested by its optical image. Our kinematic analysis indicates that the torus is expanding at 25 ± 5 km s−1 and is gradually breaking up. At an estimated distance of 7.1$_{-0.3}^{+0.8}$ kpc, the corresponding kinematic age of ∼26 000 yr is consistent with a faint and disintegrating PN. The intermediate-resolution spectra reveal an excited PN with chemical abundances typical of Type II PNe. Based on the latter, we also estimate an initial mass for the progenitor in the range 2–3 M⊙ and a central star (CSPN) mass MCSPN ∼0.61 M⊙. The Spitzer MIPS 24 μm emission that closely follows the fragmented torus could be attributed to the emission of [O iv] at 25.9 μm rather than to dust emission. All the results coherently point towards an evolved moderately massive bipolar Type II PN on the brink of dissolving into the interstellar medium.
      PubDate: Tue, 27 Oct 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3270
      Issue No: Vol. 501, No. 3 (2020)
  • Detailed studies of IPHAS sources – II. Sab 19, a true planetary
           nebula and its mimic crossing the Perseus Arm
    • Authors: Guerrero M; Ortiz R, Sabin L, et al.
      Pages: 3594 - 3604
      Abstract: ABSTRACTThe INT Photometric Hα Survey (IPHAS) has provided us with a number of new emission-line sources, among which planetary nebulae (PNe) constitute an important fraction. Here we present a detailed analysis of the IPHAS nebula Sab 19 (IPHASX J055242.8+262116) based on radio, infrared, and optical images and intermediate- and high-dispersion long-slit spectra. Sab 19 consists of a roundish 0.10 pc in radius double-shell nebula surrounded by a much larger 2.8 pc in radius external shell with a prominent H-shaped filament. We confirm the nature of the main nebula as a PN whose sub-solar N/O ratio abundances, low ionized mass, peculiar radial velocity, and low-mass central star allow us to catalogue it as a Type III PN. Apparently, the progenitor star of Sab 19 became a PN when crossing the Perseus Arm during a brief visit of a few Myr. The higher N/O ratio and velocity shift ≃ 40  km s−1 of the external shell with respect to the main nebula and its large ionized mass suggest that it is not truly associated with Sab 19, but it is rather dominated by a Strömgren zone in the interstellar medium ionized by the PN central star.
      PubDate: Tue, 27 Oct 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3082
      Issue No: Vol. 501, No. 3 (2020)
  • Detailed studies of IPHAS sources – III. The highly extinguished bipolar
           planetary nebula IPHASX J191104.8+060845
    • Authors: Rodríguez-González J; Sabin L, Toalá J, et al.
      Pages: 3605 - 3613
      Abstract: ABSTRACTWe present the first detailed study of the bipolar planetary nebula (PN) IPHASX J191104.8+060845 (PN G 040.6−01.5) discovered as part of the Isaac Newton Telescope Photometric Hα Survey of the Northern Galactic plane (IPHAS). We present Nordic Optical Telescope narrow-band images to unveil its true morphology. This PN consists of a main cavity with two newly uncovered extended low-surface brightness lobes located towards the NW and SE directions. Using near-IR WISE images we unveiled the presence of a barrel-like structure, which surrounds the main cavity, which would explain the dark lane towards the equatorial regions. We also use Gran Telescopio de Canarias spectra to study the physical properties of this PN. We emphasize the potential of old PNe detected in IPHAS to study the final stages of the evolution of the circumstellar medium around solar-like stars.
      PubDate: Tue, 27 Oct 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3037
      Issue No: Vol. 501, No. 3 (2020)
  • Distances to PHANGS galaxies: New tip of the red giant branch measurements
           and adopted distances
    • Authors: Anand G; Lee J, Van Dyk S, et al.
      Pages: 3621 - 3639
      Abstract: ABSTRACTPHANGS-HST is an ultraviolet-optical imaging survey of 38 spiral galaxies within ∼20 Mpc. Combined with the PHANGS-ALMA, PHANGS-MUSE surveys and other multiwavelength data, the data set will provide an unprecedented look into the connections between young stars, H ii regions, and cold molecular gas in these nearby star-forming galaxies. Accurate distances are needed to transform measured observables into physical parameters (e.g. brightness to luminosity, angular to physical sizes of molecular clouds, star clusters and associations). PHANGS-HST has obtained parallel ACS imaging of the galaxy haloes in the F606W and F814W bands. Where possible, we use these parallel fields to derive tip of the red giant branch (TRGB) distances to these galaxies. In this paper, we present TRGB distances for 10 PHANGS galaxies from ∼4 to ∼15 Mpc, based on the first year of PHANGS-HST observations. Four of these represent the first published TRGB distance measurements (IC 5332, NGC 2835, NGC 4298, and NGC 4321), and seven of which are the best available distances to these targets. We also provide a compilation of distances for the 118 galaxies in the full PHANGS sample, which have been adopted for the first PHANGS-ALMA public data release.
      PubDate: Wed, 25 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3668
      Issue No: Vol. 501, No. 3 (2020)
  • Cosmic ray driven outflows to Mpc scales from L* galaxies
    • Authors: Hopkins P; Chan T, Ji S, et al.
      Pages: 3640 - 3662
      Abstract: ABSTRACTWe study the effects of cosmic rays (CRs) on outflows from star-forming galaxies in the circum and intergalactic medium (CGM/IGM), in high-resolution, fully cosmological FIRE-2 simulations (accounting for mechanical and radiative stellar feedback, magnetic fields, anisotropic conduction/viscosity/CR diffusion and streaming, and CR losses). We showed previously that massive ($M_{\rm halo}\gtrsim 10^{11}\, \mathrm{M}_{\odot }$), low-redshift (z ≲ 1–2) haloes can have CR pressure dominate over thermal CGM pressure and balance gravity, giving rise to a cooler CGM with an equilibrium density profile. This dramatically alters outflows. Absent CRs, high gas thermal pressure in massive haloes ‘traps’ galactic outflows near the disc, so they recycle. With CRs injected in supernovae as modelled here, the low-pressure halo allows ‘escape’ and CR pressure gradients continuously accelerate this material well into the IGM in ‘fast’ outflows, while lower-density gas at large radii is accelerated in situ into ‘slow’ outflows that extend to >Mpc scales. CGM/IGM outflow morphologies are radically altered: they become mostly volume-filling (with inflow in a thin mid-plane layer) and coherently biconical from the disc to >Mpc. The CR-driven outflows are primarily cool ($T\sim \! 10^{5}\,$ K) and low velocity. All of these effects weaken and eventually vanish at lower halo masses ($\lesssim 10^{11}\, \mathrm{M}_{\odot }$) or higher redshifts (z ≳ 1–2), reflecting the ratio of CR to thermal + gravitational pressure in the outer halo. We present a simple analytical model that explains all of the above phenomena. We caution that these predictions may depend on uncertain CR transport physics.
      PubDate: Sat, 28 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3690
      Issue No: Vol. 501, No. 3 (2020)
  • Effects of different cosmic ray transport models on galaxy formation
    • Authors: Hopkins P; Chan T, Squire J, et al.
      Pages: 3663 - 3669
      Abstract: ABSTRACTCosmic rays (CRs) with ∼GeV energies can contribute significantly to the energy and pressure budget in the interstellar, circumgalactic, and intergalactic medium (ISM, CGM, IGM). Recent cosmological simulations have begun to explore these effects, but almost all studies have been restricted to simplified models with constant CR diffusivity and/or streaming speeds. Physical models of CR propagation/scattering via extrinsic turbulence and self-excited waves predict transport coefficients which are complicated functions of local plasma properties. In a companion paper, we consider a wide range of observational constraints to identify proposed physically motivated cosmic ray propagation scalings which satisfy both detailed Milky Way (MW) and extragalactic γ-ray constraints. Here, we compare the effects of these models relative to simpler ‘diffusion+streaming’ models on galaxy and CGM properties at dwarf through MW mass scales. The physical models predict large local variations in CR diffusivity, with median diffusivity increasing with galactocentric radii and decreasing with galaxy mass and redshift. These effects lead to a more rapid dropoff of CR energy density in the CGM (compared to simpler models), in turn producing weaker effects of CRs on galaxy star formation rates (SFRs), CGM absorption profiles, and galactic outflows. The predictions of the more physical CR models tend to lie ‘in between’ models which ignore CRs entirely and models which treat CRs with constant diffusivity.
      PubDate: Sat, 28 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3692
      Issue No: Vol. 501, No. 3 (2020)
  • Creation/destruction of ultra-wide binaries in tidal streams
    • Authors: Peñarrubia J.
      Pages: 3670 - 3686
      Abstract: ABSTRACTThis paper uses statistical and N-body methods to explore a new mechanism to form binary stars with extremely large separations (${\gtrsim}0.1\, {\rm pc}$), whose origin is poorly understood. Here, ultra-wide binaries arise via chance entrapment of unrelated stars in tidal streams of disrupting clusters. It is shown that (i) the formation of ultra-wide binaries is not limited to the lifetime of a cluster, but continues after the progenitor is fully disrupted, (ii) the formation rate is proportional to the local phase-space density of the tidal tails, (iii) the semimajor axis distribution scales as p(a)da ∼ a1/2da at a ≪ D, where D is the mean interstellar distance, and (vi) the eccentricity distribution is close to thermal, p(e)de = 2ede. Owing to their low binding energies, ultra-wide binaries can be disrupted by both the smooth tidal field and passing substructures. The time-scale on which tidal fluctuations dominate over the mean field is inversely proportional to the local density of compact substructures. Monte Carlo experiments show that binaries subject to tidal evaporation follow p(a)da ∼ a−1da at a ≳ apeak, known as Öpik’s law, with a peak semimajor axis that contracts with time as apeak ∼ t−3/4. In contrast, a smooth Galactic potential introduces a sharp truncation at the tidal radius, p(a) ∼ 0 at a ≳ rt. The scaling relations of young clusters suggest that most ultra-wide binaries arise from the disruption of low-mass systems. Streams of globular clusters may be the birthplace of hundreds of ultra-wide binaries, making them ideal laboratories to probe clumpiness in the Galactic halo.
      PubDate: Mon, 30 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3700
      Issue No: Vol. 501, No. 3 (2020)
  • Galaxy mass profiles from strong lensing – III. The two-dimensional
           broken power-law model
    • Authors: O’Riordan C; Warren S, Mortlock D.
      Pages: 3687 - 3694
      Abstract: ABSTRACTWhen modelling strong gravitational lenses, i.e. where there are multiple images of the same source, the most widely used parametrization for the mass profile in the lens galaxy is the singular power-law model ρ(r)∝r−γ. This model may be insufficiently flexible for very accurate work, for example, measuring the Hubble constant based on time delays between multiple images. Here, we derive the lensing properties – deflection angle, shear, and magnification – of a more adaptable model where the projected mass surface density is parametrized as a continuous two-dimensional broken power law (2DBPL). This elliptical 2DBPL model is characterized by power-law slopes t1 and t2 either side of the break radius θB. The key to the 2DBPL model is the derivation of the lensing properties of the truncated power-law (TPL) model, where the surface density is a power law out to the truncation radius θT and zero beyond. This TPL model is also useful by itself. We create mock observations of lensing by a TPL profile where the images form outside the truncation radius, so there is no mass in the annulus covered by the images. We then show that the slope of the profile interior to the images may be accurately recovered for lenses of moderate ellipticity. This demonstrates that the widely held notion that lensing measures the slope of the mass profile in the annulus of the images, and is insensitive to the mass distribution at radii interior to the images, is incorrect.
      PubDate: Tue, 08 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3747
      Issue No: Vol. 501, No. 3 (2020)
  • Spatially resolved direct method metallicity in a high-redshift analogue
           local galaxy: temperature structure impact on metallicity gradients
    • Authors: Cameron A; Yuan T, Trenti M, et al.
      Pages: 3695 - 3714
      Abstract: ABSTRACTWe investigate how H ii region temperature structure assumptions affect ‘direct-method’ spatially resolved metallicity observations using multispecies auroral lines in a galaxy from the SAMI Galaxy Survey. SAMI609396B, at redshift z = 0.018, is a low-mass galaxy in a minor merger with intense star formation, analogous to conditions at high redshifts. We use three methods to derive direct metallicities and compare with strong-line diagnostics. The spatial metallicity trends show significant differences among the three direct methods. Our first method is based on the commonly used electron temperature Te([O iii]) from the [O iii]λ4363 auroral line and a traditional Te([O ii]) – Te([O iii]) calibration. The second method applies a recent empirical correction to the O+ abundance from the [O iii]/[O ii] strong-line ratio. The third method infers the Te([O ii]) from the [S ii]λλ4069,76 auroral lines. The first method favours a positive metallicity gradient along SAMI609396B, whereas the second and third methods yield flattened gradients. Strong-line diagnostics produce mostly flat gradients, albeit with unquantified contamination from shocked regions. We conclude that overlooked assumptions about the internal temperature structure of H ii regions in the direct method can lead to large discrepancies in metallicity gradient studies. Our detailed analysis of SAMI609396B underlines that high-accuracy metallicity gradient measurements require a wide array of emission lines and improved spatial resolutions in order to properly constrain excitation sources, physical conditions, and temperature structures of the emitting gas. Integral-field spectroscopic studies with future facilities such as JWST/NIRSpec and ground-based ELTs will be crucial in minimizing systematic effects on measured gradients in distant galaxies.
      PubDate: Tue, 08 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3757
      Issue No: Vol. 501, No. 3 (2020)
  • RoboPol: AGN polarimetric monitoring data
    • Authors: Blinov D; Kiehlmann S, Pavlidou V, et al.
      Pages: 3715 - 3726
      Abstract: ABSTRACTWe present uniformly reprocessed and re-calibrated data from the RoboPol programme of optopolarimetric monitoring of active galactic nuclei (AGNs), covering observations between 2013, when the instrument was commissioned, and 2017. In total, the data set presented in this paper includes 5068 observations of 222 AGN with Dec. > −25○. We describe the current version of the RoboPol pipeline that was used to process and calibrate the entire data set, and we make the data publicly available for use by the astronomical community. Average quantities summarizing optopolarimetric behaviour (average degree of polarization, polarization variability index) are also provided for each source we have observed and for the time interval we have followed it.
      PubDate: Wed, 16 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3777
      Issue No: Vol. 501, No. 3 (2020)
  • Model-independent discovery prospects for primordial black holes at LIGO
    • Authors: Lehmann B; Profumo S, Yant J.
      Pages: 3727 - 3740
      Abstract: ABSTRACTPrimordial black holes may encode the conditions of the early Universe, and may even constitute a significant fraction of cosmological dark matter. Their existence has yet to be established. However, black holes with masses below ${\sim}{1}{\, \mathrm{M}_\odot }$ cannot form as an endpoint of stellar evolution, so the detection of even one such object would be a smoking gun for new physics, and would constitute evidence that at least a fraction of the dark matter consists of primordial black holes. Gravitational wave detectors are capable of making a definitive discovery of this kind by detecting mergers of light black holes. But since the merger rate depends strongly on the shape of the black hole mass function, it is difficult to determine the potential for discovery or constraint as a function of the overall abundance of black holes. Here, we directly maximize and minimize the merger rate to connect observational results to the actual abundance of observable objects. We show that LIGO can discover mergers of light primordial black holes within the next decade even if such black holes constitute only a very small fraction of dark matter. A single merger event involving such an object would (i) provide conclusive evidence of new physics, (ii) establish the nature of some fraction of dark matter, and (iii) probe cosmological history at scales far beyond those observable today.
      PubDate: Thu, 10 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3806
      Issue No: Vol. 501, No. 3 (2020)
  • X-ray dips in AGNs and microquasars – collapse time-scales of inner
           accretion disc
    • Authors: Shende M; Chauhan P, Subramanian P.
      Pages: 3741 - 3749
      Abstract: ABSTRACTThe temporal behaviour of X-rays from some AGNs and microquasars is thought to arise from the rapid collapse of the hot, inner parts of their accretion discs. The collapse can occur over the radial infall time-scale of the inner accretion disc. However, estimates of this time-scale are hindered by a lack of knowledge of the operative viscosity in the collisionless plasma comprising the inner disc. We use published simulation results for cosmic ray diffusion through turbulent magnetic fields to arrive at a viscosity prescription appropriate to hot accretion discs. We construct simplified disc models using this viscosity prescription and estimate disc collapse time-scales for 3C 120, 3C 111, and GRS 1915+105. The Shakura–Sunyaev α parameter resulting from our model ranges from 0.02 to 0.08. Our inner disc collapse time-scale estimates agree well with those of the observed X-ray dips. We find that the collapse time-scale is most sensitive to the outer radius of the hot accretion disc.
      PubDate: Sat, 12 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3838
      Issue No: Vol. 501, No. 3 (2020)
  • Joint Suzaku and Chandra observations of the MKW4 galaxy group out to the
           virial radius
    • Authors: Sarkar A; Su Y, Randall S, et al.
      Pages: 3767 - 3780
      Abstract: ABSTRACTWe present joint Suzaku and Chandra observations of MKW4. With a global temperature of 1.6 keV, MKW4 is one of the smallest galaxy groups that have been mapped in X-rays out to the virial radius. We measure its gas properties from its centre to the virial radius in the north, east, and north-east directions. Its entropy profile follows a power law of ∝r1.1 between R500 and R200 in all directions, as expected from the purely gravitational structure formation model. The well-behaved entropy profiles at the outskirts of MKW4 disfavour the presence of gas clumping or thermal non-equilibrium between ions and electrons in this system. We measure an enclosed baryon fraction of 11 per cent at R200, remarkably smaller than the cosmic baryon fraction of 15 per cent. We note that the enclosed gas fractions at R200 are systematically smaller for groups than for clusters from existing studies in the literature. The low baryon fraction of galaxy groups, such as MKW4, suggests that their shallower gravitational potential well may make them more vulnerable to baryon losses due to active galactic nucleus feedback or galactic winds. We find that the azimuthal scatter of various gas properties at the outskirts of MKW4 is significantly lower than in other systems, suggesting that MKW4 is a spherically symmetric and highly relaxed system.
      PubDate: Thu, 17 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3858
      Issue No: Vol. 501, No. 3 (2020)
  • Accretion and outflow activity in proto-brown dwarfs
    • Authors: Riaz B; Bally J.
      Pages: 3781 - 3805
      Abstract: ABSTRACTWe present a near-infrared study of accretion and outflow activity in six Class 0/I proto-brown dwarfs (proto-BDs) using VLT/SINFONI spectroscopy and spectroimaging observations. The spectra show emission in several [Fe ii] and H2 lines associated with jet/outflow activity, and in the accretion diagnostics of Pa β and Br γ lines. The peak velocities of the [Fe ii] lines (>100 km s−1) are higher than the H2 lines. The Class 0 proto-BDs show strong emission in the H2 lines but the [Fe ii] lines are undetected, while the Class I objects show emission in both [Fe ii] and H2 lines, suggesting an evolutionary trend in the jets from a molecular to an ionic composition. Extended emission with knots is seen in the [Fe ii] and H2 spectroimages for three proto-BDs, while the rest show compact morphologies with a peak on-source. The accretion rates for the proto-BDs span the range of (2 × 10−6–2 × 10−8) M⊙ yr−1, while the mass-loss rates are in the range of (4 × 10−8–5 × 10−9) M⊙ yr−1. These rates are within the range measured for low-mass protostars and higher than Class II brown dwarfs. We find a similar range in the jet efficiency for proto-BDs as measured in protostars. We have performed a study of the Brackett decrement from the Br 7–19 lines detected in the proto-BDs. The upper Brackett lines of Br 13–19 are only detected in the earlier stage systems. The ratios of the different Brackett lines with respect to the Br γ line intensity are consistent with the ratios expected from Case B recombination.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3905
      Issue No: Vol. 501, No. 3 (2020)
  • Circularization of tidal debris around white dwarfs: implications for gas
           production and dust variability
    • Authors: Malamud U; Grishin E, Brouwers M.
      Pages: 3806 - 3824
      Abstract: ABSTRACTWhite dwarf (WD) pollution is thought to arise from the tidal disruption of planetary bodies. The initial fragment stream is extremely eccentric, while observational evidence suggest that discs are circular or nearly so. Here, we propose a novel mechanism to bridge this gap and show that the fragments can rapidly circularize through dust or gas drag when they interact with a pre-existing compact disc. We assume that the tidal stream mainly consists of small cohesive fragments in the size range 10–1000 m, capable of resisting the WD tidal forces, whereas the compact discs span a wide mass range. We provide an analytical model, accompanied by N-body simulations, and find a large parameter space in fragment sizes and orbital separation that leads to full circularization. Partial circularization is possible for compact discs that are several orders of magnitudes less massive. We show that dust-induced circularization inherently produces gas as tidal fragments collisionally vapourize the pre-existing dust along their path. We show that ongoing gas production has a higher probability to occur during the early stages of tidal disruption events, resulting from the fact that smaller fragments are the first to circularize. Intermittent gas production however becomes more likely as the tidal stream matures. This could explain why only a small subset of systems with dusty compact discs also have an observed gaseous component. Additionally, the interaction yields fragment erosion by collisional shattering, sputtering, sublimation, and possibly ram pressure. Material scattered by the collisions might form a thin dusty halo that evolves through Poynting–Robertson drag, in compatibility with observed infrared variability.
      PubDate: Wed, 23 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3940
      Issue No: Vol. 501, No. 3 (2020)
  • Joint inference on the redshift distribution of fast radio burst and on
           the intergalactic baryon content
    • Authors: Hackstein S; Brüggen M, Vazza F.
      Pages: 3825 - 3832
      Abstract: ABSTRACTFast radio bursts are transient radio pulses of extragalactic origin. Their dispersion measure is indicative of the baryon content in the ionized intergalactic medium between the source and the observer. However, inference using unlocalized fast radio bursts is degenerate to the distribution of redshifts of host galaxies. We perform a joint inference of the intergalactic baryon content and the fast radio burst redshift distribution with the use of Bayesian statistics by comparing the likelihood of different models to reproduce the observed statistics in order to infer the most likely models. In addition to two models of the intergalactic medium, we consider contributions from the local environment of the source, assumed to be a magnetar, as well as a representative ensemble of host and intervening galaxies. Assuming that the missing baryons reside in the ionized intergalactic medium, our results suggest that the redshift distribution of observed fast radio bursts peaks at z ≲ 0.6. However, conclusions from different instruments regarding the intergalactic baryon content diverge and thus require additional changes to the observed distribution of host redshifts, beyond those caused by telescope selection effects.
      PubDate: Thu, 24 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3963
      Issue No: Vol. 501, No. 3 (2020)
  • A quantitative in-depth analysis of the prototype sdB+BD system
           SDSS J08205+0008 revisited in the Gaia era
    • Authors: Schaffenroth V; Casewell S, Schneider D, et al.
      Pages: 3847 - 3870
      Abstract: ABSTRACTSubdwarf B stars are core-helium-burning stars located on the extreme horizontal branch (EHB). Extensive mass loss on the red giant branch is necessary to form them. It has been proposed that substellar companions could lead to the required mass loss when they are engulfed in the envelope of the red giant star. J08205+0008 was the first example of a hot subdwarf star with a close, substellar companion candidate to be found. Here, we perform an in-depth re-analysis of this important system with much higher quality data allowing additional analysis methods. From the higher resolution spectra obtained with ESO-VLT/XSHOOTER, we derive the chemical abundances of the hot subdwarf as well as its rotational velocity. Using the Gaia parallax and a fit to the spectral energy distribution in the secondary eclipse, tight constraints to the radius of the hot subdwarf are derived. From a long-term photometric campaign, we detected a significant period decrease of $-3.2(8)\times 10^{-12} \, \rm dd^{-1}$. This can be explained by the non-synchronized hot subdwarf star being spun up by tidal interactions forcing it to become synchronized. From the rate of period decrease we could derive the synchronization time-scale to be 4 Myr, much smaller than the lifetime on EHB. By combining all different methods, we could constrain the hot subdwarf to a mass of $0.39\!-\!0.50\, \rm M_\odot$ and a radius of $R_{\rm sdB}=0.194\pm 0.008\, \rm R_\odot$, and the companion to $0.061\!-\!0.071\rm \, M_\odot$ with a radius of $R_{\rm comp}=0.092 \pm 0.005\, \rm R_\odot$, below the hydrogen-burning limit. We therefore confirm that the companion is most likely a massive brown dwarf.
      PubDate: Wed, 25 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3661
      Issue No: Vol. 501, No. 3 (2020)
  • On the pumping of the CS(υ = 0) masers in W51 e2e
    • Authors: van der Walt D; Ginsburg A, Goddi C.
      Pages: 3871 - 3882
      Abstract: ABSTRACTWe present the results of numerically solving the rate equations for the first 31 rotational states of CS in the ground vibrational state to determine the conditions under which the J = 1 − 0, J = 2 − 1, and J = 3 − 2 transitions are inverted to produce maser emission. The essence of our results is that the CS($\upsilon \!=\!0$) masers are collisionally pumped and that, depending on the spectral energy distribution, dust emission can suppress the masers. Apart from the J = 1 − 0 and J = 2 − 1 masers, the calculations also show that the J = 3 − 2 transition can be inverted to produce maser emission. It is found that beaming is necessary to explain the observed brightness temperatures of the recently discovered CS masers in W51 e2e. The model calculations suggest that a CS abundance of a few times 10−5 and CS($\upsilon \!=\!0$) column densities of the order of $10^{16}\, \mathrm{cm^{-2}}$ are required for these masers. The rarity of the CS masers in high-mass star-forming regions might be the result of a required high CS abundance as well as due to attenuation of the maser emission inside as well as outside of the hot core.
      PubDate: Thu, 26 Nov 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3667
      Issue No: Vol. 501, No. 3 (2020)
  • The PAU survey: Ly α intensity mapping forecast
    • Authors: Renard P; Gaztanaga E, Croft R, et al.
      Pages: 3883 - 3899
      Abstract: ABSTRACTIn this work, we explore the application of intensity mapping to detect extended Ly α emission from the IGM via cross-correlation of PAUS images with Ly α forest data from eBOSS and DESI. Seven narrow-band (FWHM = 13 nm) PAUS filters have been considered, ranging from 455 to 515 nm in steps of 10 nm, which allows the observation of Ly α emission in a range 2.7 < z < 3.3. The cross-correlation is simulated first in an area of 100 deg2 (PAUS projected coverage), and second in two hypothetical scenarios: a deeper PAUS (complete up to iAB < 24 instead of iAB < 23, observation time ×6), and an extended PAUS coverage of 225 deg2 (observation time ×2.25). A hydrodynamic simulation of size 400 Mpc h−1 is used to simulate both extended Ly α emission and absorption, while the foregrounds in PAUS images have been simulated using a lightcone mock catalogue. Using an optimistic estimation of uncorrelated PAUS noise, the total probability of a non-spurious detection is estimated to be 1.8 per cent and 4.5 per cent for PAUS-eBOSS and PAUS-DESI, from a run of 1000 simulated cross-correlations with different realisations of instrumental noise and quasar positions. The hypothetical PAUS scenarios increase this probability to 15.3 per cent (deeper PAUS) and 9.0 per cent (extended PAUS). With realistic correlated noise directly measured from PAUS images, these probabilities become negligible. Despite these negative results, some evidences suggest that this methodology may be more suitable to broad-band surveys.
      PubDate: Tue, 08 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3783
      Issue No: Vol. 501, No. 3 (2020)
  • Detection of giant pulses in PSR J1047−6709
    • Authors: Sun S; Yan W, Wang N.
      Pages: 3900 - 3904
      Abstract: ABSTRACTWe report the emission variations in PSR J1047−6709 observed at 1369 MHz using the Parkes 64-m radio telescope. This pulsar shows two distinct emission states: a weak state and a bright emission state. We detected giant pulses (GPs) in the bright state for the first time. We found 75 GPs with pulse width ranging from 0.6 to 2.6 ms. The energy of GPs follows a power-law distribution with the index α = −3.26 ± 0.22. The peak flux density of the brightest GP is 19 Jy which is 110 times stronger than the mean pulse profile. The polarization properties of the average profile of GPs are similar to that of the pulses with energy less than 10 times average pulse energy in the bright state. This indicates that the emission mechanism is basically the same for them. Our results provide a new insight into the origin of the GPs in pulsars.
      PubDate: Fri, 11 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3825
      Issue No: Vol. 501, No. 3 (2020)
  • Dust reverberation mapping of Z229–15
    • Authors: Mandal A; Rakshit S, Stalin C, et al.
      Pages: 3905 - 3915
      Abstract: ABSTRACTWe report results of the dust reverberation mapping (DRM) on the Seyfert 1 galaxy Z229–15 at z = 0.0273. Quasi-simultaneous photometric observations for a total of 48 epochs were acquired during the period 2017 July to 2018 December in B, V, J, H and Ks bands. The calculated spectral index (α) between B and V bands for each epoch was used to correct for the accretion disc (AD) component present in the infrared light curves. The observed α ranges between −0.99 and 1.03. Using cross-correlation function analysis we found significant time delays between the optical V and the AD corrected J, H and Ks light curves. The lags in the rest frame of the source are $12.52^{+10.00}_{-9.55}$ d (between V and J), $15.63^{+5.05}_{-5.11}$ d (between V and H) and $20.36^{+5.82}_{-5.68}$ d (between V and Ks). Given the large error bars, these lags are consistent with each other. However, considering the lag between V and Ks bands to represent the inner edge of the dust torus, the torus in Z229–15 lies at a distance of 0.017 pc from the central ionizing continuum. This is smaller than that expected from the radius luminosity (R−L) relationship known from DRM. Using a constant α = 0.1 to account for the AD component, as is normally done in DRM, the deduced radius (0.025 pc) lies close to the expected R−L relation. However, usage of constant α in DRM is disfavoured as the α of the ionizing continuum changes with the flux of the source.
      PubDate: Sat, 12 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3828
      Issue No: Vol. 501, No. 3 (2020)
  • Serendipitous discovery of a dusty disc around
    • Authors: González Egea E; Raddi R, Koester D, et al.
      Pages: 3916 - 3925
      Abstract: ABSTRACTSpectroscopic observations of white dwarfs reveal that many of them are polluted by exoplanetary material, whose bulk composition can be uniquely probed this way. We present a spectroscopic and photometric analysis of the DA white dwarf WDJ181417.84−735459.83, an object originally identified to have a strong infrared (IR) excess in the 2MASS and WISE catalogues that we confirmed to be intrinsic to the white dwarf, and likely corresponding to the emission of a dusty disc around the star. The finding of Ca, Fe, and Mg absorption lines in two X-SHOOTER spectra of the white dwarf, taken 8 years apart, is further evidence of accretion from a dusty disc. We do not report variability in the absorption lines between these two spectra. Fitting a blackbody model to the IR excess gives a temperature of 910 ± 50 K. We have estimated a total accretion flux from the spectroscopic metal lines of $ \dot{\rm M} = 1.784 \times 10^{9}\,$g s−1.
      PubDate: Sat, 12 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3836
      Issue No: Vol. 501, No. 3 (2020)
  • An ALMA/NOEMA survey of the molecular gas properties of high-redshift
           star-forming galaxies
    • Authors: Birkin J; Weiss A, Wardlow J, et al.
      Pages: 3926 - 3950
      Abstract: ABSTRACTWe have used ALMA and NOEMA to study the molecular gas reservoirs in 61 ALMA-identified submillimetre galaxies (SMGs) in the COSMOS, UDS, and ECDFS fields. We detect 12CO ($J_{\rm up} =$ 2–5) emission lines in 50 sources, and [C i](3P1 − 3P0) emission in eight, at $z =$ 1.2–4.8 and with a median redshift of 2.9 ± 0.2. By supplementing our data with literature sources, we construct a statistical CO spectral line energy distribution and find that the 12CO line luminosities in SMGs peak at Jup ∼ 6, consistent with similar studies. We also test the correlations of the CO, [C i], and dust as tracers of the gas mass, finding the three to correlate well, although the CO and dust mass as estimated from the 3-mm continuum are preferable. We estimate that SMGs lie mostly on or just above the star-forming main sequence, with a median gas depletion timescale, tdep = Mgas/SFR, of 210 ± 40 Myr for our sample. Additionally, tdep declines with redshift across z ∼ 1–5, while the molecular gas fraction, μgas = Mgas/M*, increases across the same redshift range. Finally, we demonstrate that the distribution of total baryonic mass and dynamical line width, Mbaryon–σ, for our SMGs is consistent with that followed by early-type galaxies in the Coma cluster, providing strong support to the suggestion that SMGs are progenitors of massive local spheroidal galaxies. On the basis of this, we suggest that the SMG populations above and below an 870-μm flux limit of S870 ∼ 5 mJy may correspond to the division between slow and fast rotators seen in local early-type galaxies.
      PubDate: Thu, 17 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3862
      Issue No: Vol. 501, No. 3 (2020)
  • An active galactic nucleus recognition model based on deep neural network
    • Authors: Chen B; Goto T, Kim S, et al.
      Pages: 3951 - 3961
      Abstract: ABSTRACTTo understand the cosmic accretion history of supermassive black holes, separating the radiation from active galactic nuclei (AGNs) and star-forming galaxies (SFGs) is critical. However, a reliable solution on photometrically recognizing AGNs still remains unsolved. In this work, we present a novel AGN recognition method based on Deep Neural Network (Neural Net; NN). The main goals of this work are (i) to test if the AGN recognition problem in the North Ecliptic Pole Wide (NEPW) field could be solved by NN; (ii) to show that NN exhibits an improvement in the performance compared with the traditional, standard spectral energy distribution (SED) fitting method in our testing samples; and (iii) to publicly release a reliable AGN/SFG catalogue to the astronomical community using the best available NEPW data, and propose a better method that helps future researchers plan an advanced NEPW data base. Finally, according to our experimental result, the NN recognition accuracy is around 80.29 per cent–85.15 per cent, with AGN completeness around 85.42 per cent–88.53 per cent and SFG completeness around 81.17 per cent–85.09 per cent.
      PubDate: Thu, 17 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3865
      Issue No: Vol. 501, No. 3 (2020)
  • Dissecting the stellar content of Leo I: a dwarf irregular caught in
    • Authors: Ruiz-Lara T; Gallart C, Monelli M, et al.
      Pages: 3962 - 3980
      Abstract: ABSTRACTLeo I is considered one of the youngest dwarf spheroidals (dSph) in the Local Group. Its isolation, extended star formation history (SFH), and recent perigalacticon passage (∼1 Gyr ago) make Leo I one of the most interesting nearby stellar systems. Here, we analyse deep photometric Hubble Space Telescope data via colour–magnitude diagram fitting techniques to study its global and radially resolved SFH. We find global star formation enhancements in Leo I ∼13, 5.5, 2.0, and 1.0 Gyr ago, after which it was substantially quenched. Within the context of previous works focused on Leo I, we interpret the most ancient and the youngest ones as being linked to an early formation (surviving reionization) and the latest perigalacticon passage (transition from dIrr to dSph), respectively. We clearly identify the presence of very metal poor stars ([Fe/H] ∼ −2) ageing ∼5–6 and ∼13 Gyr old. We speculate with the possibility that this metal-poor population in Leo I is related to the merging with a low-mass system (possibly an ultra-faint dwarf). This event would have triggered star formation (peak of star formation ∼5.5 Gyr ago) and accumulated old, metal-poor stars from the accreted system in Leo I. Some of the stars born during this event would also form from accreted gas of low-metallicity (giving rise to the 5–6 Gyr low-metallicity tail). Given the intensity and extension of the 2.0 Gyr burst, we hypothesize that this enhancement could also have an external origin. Despite the quenching of star formation around 1 Gyr ago (most probably induced by ram pressure stripping with the Milky Way halo at pericentre), we report the existence of stars as young as 300–500 Myr. We also distinguish two clear spatial regions: the inner ∼190 pc presents a homogeneous stellar content (size of the gaseous star forming disc in Leo I from ∼4.5 to 1 Gyr ago), whereas the outer regions display a clear positive age gradient.
      PubDate: Thu, 17 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3871
      Issue No: Vol. 501, No. 3 (2020)
  • Magnetic field and chromospheric activity evolution of HD 75332: a rapid
           magnetic cycle in an F star without a hot Jupiter
    • Authors: Brown E; Marsden S, Mengel M, et al.
      Pages: 3981 - 4003
      Abstract: ABSTRACTStudying cool star magnetic activity gives an important insight into the stellar dynamo and its relationship with stellar properties, as well as allowing us to place the Sun’s magnetism in the context of other stars. Only 61 Cyg A (K5V) and τ Boo (F8V) are currently known to have magnetic cycles like the Sun’s, where the large-scale magnetic field polarity reverses in phase with the star’s chromospheric activity cycles. τ Boo has a rapid ∼240 d magnetic cycle, and it is not yet clear whether this is related to the star’s thin convection zone or if the dynamo is accelerated by interactions between τ Boo and its hot Jupiter. To shed light on this, we studied the magnetic activity of HD 75332 (F7V) which has similar physical properties to τ Boo and does not appear to host a hot Jupiter. We characterized its long-term chromospheric activity variability over 53 yr and used Zeeman Doppler Imaging to reconstruct the large-scale surface magnetic field for 12 epochs between 2007 and 2019. Although we observe only one reversal of the large-scale magnetic dipole, our results suggest that HD 75332 has a rapid ∼1.06 yr solar-like magnetic cycle where the magnetic field evolves in phase with its chromospheric activity. If a solar-like cycle is present, reversals of the large-scale radial field polarity are expected to occur at around activity cycle maxima. This would be similar to the rapid magnetic cycle observed for τ Boo, suggesting that rapid magnetic cycles may be intrinsic to late-F stars and related to their shallow convection zones.
      PubDate: Fri, 18 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3878
      Issue No: Vol. 501, No. 3 (2020)
  • A faster Fourier transform' Computing small-scale power spectra and
           bispectra for cosmological simulations in 𝒪(N2) time
    • Authors: Philcox O.
      Pages: 4004 - 4034
      Abstract: ABSTRACTWe present $\mathcal {O}(N^2)$ estimators for the small-scale power spectrum and bispectrum in cosmological simulations. In combination with traditional methods, these allow spectra to be efficiently computed across a vast range of scales, requiring orders of magnitude less computation time than Fast Fourier Transform based approaches alone. These methods are applicable to any tracer; simulation particles, haloes or galaxies, and take advantage of the simple geometry of the box and periodicity to remove almost all dependence on large random particle catalogues. By working in configuration-space, both power spectra and bispectra can be computed via a weighted sum of particle pairs up to some radius, which can be reduced at larger k, leading to algorithms with decreasing complexity on small scales. These do not suffer from aliasing or shot-noise, allowing spectra to be computed to arbitrarily large wavenumbers. The estimators are rigorously derived and tested against simulations, and their covariances discussed. The accompanying code, hipster, has been publicly released, incorporating these algorithms. Such estimators will be of great use in the analysis of large sets of high-resolution simulations.
      PubDate: Fri, 18 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3882
      Issue No: Vol. 501, No. 3 (2020)
  • A physico-chemical model to study the ion density distribution in the
           inner coma of comet C/2016 R2 (Pan-STARRS)
    • Authors: Raghuram S; Bhardwaj A, Hutsemékers D, et al.
      Pages: 4035 - 4052
      Abstract: ABSTRACTThe recent observations show that comet C/2016 R2 (Pan-Starrs) has a unique and peculiar composition when compared with several other comets observed at 2.8 au heliocentric distance. Assuming solar resonance fluorescence is the only excitation source, the observed ionic emission intensity ratios are used to constrain the corresponding neutral abundances in this comet. We developed a physico-chemical model to study the ion density distribution in the inner coma of this comet by accounting for photon and electron impact ionization of neutrals, charge exchange and proton transfer reactions between ions and neutrals, and electron–ion thermal recombination reactions. Our calculations show that CO2+ and CO+ are the major ions in the inner coma, and close to the surface of nucleus CH3OH+, CH3OH2+, and O2+ are also important ions. By considering various excitation sources, we also studied the emission mechanisms of different excited states of CO+, CO2+, N2+, and H2O+. We found that the photon and electron impact ionization and excitation of corresponding neutrals significantly contribute to the observed ionic emissions for radial distances smaller than 300 km and at larger distances, solar resonance fluorescence is the major excitation source. Our modelled ion emission intensity ratios are consistent with the ground-based observations. Based on the modelled emission processes, we suggest that the observed ion emission intensity ratios can be used to derive the neutral composition in the cometary coma only when the ion densities are significantly controlled by photon and photoelectron impact ionization of neutrals rather than by the ion–neutral chemistry.
      PubDate: Fri, 18 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3885
      Issue No: Vol. 501, No. 3 (2020)
  • Simulating the inflation of bubbles by late jets in core collapse
           supernova ejecta
    • Authors: Akashi M; Soker N.
      Pages: 4053 - 4063
      Abstract: ABSTRACTWe conducted 3D hydrodynamical simulations to study the interaction of two late opposite jets with the ejecta of a core collapse supernova (CCSN), and study the bipolar structure that results from this interaction as the jets inflate hot-low-density bubbles. The newly born central object, a neutron star (NS; or a black hole), launches these jets at about 50 to 100 d after explosion. The bubbles cross the photosphere in the polar directions at much earlier times than the regions at the same radii near the equatorial plane. The hot bubbles releases more radiation and the photosphere recedes more rapidly in the tenuous bubble. Our results strengthen earlier claims that were based on toy models that such an interaction might lead to a late peak in the light curve, and that an equatorial observer might see a rapid drop in the light curve. Our results might have implications to much earlier jets that explode the star, either jets that the newly born NS launches in a CCSN, or jets that an NS companion that merges with the core of a massive star launches in a common envelope jets supernova (CEJSN) event. Our results add indirect support to the CEJSN scenario for fast blue optical transients, e.g. AT2018cow, ZTF18abvkwla, and CSS161010.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3897
      Issue No: Vol. 501, No. 3 (2020)
  • Determining star formation rates in active galactic nuclei hosts via
           stellar population synthesis
    • Authors: Riffel R; Mallmann N, Ilha G, et al.
      Pages: 4064 - 4079
      Abstract: ABSTRACTThe effect of active galactic nuclei (AGNs) feedback on the host galaxy, and its role in quenching or enhancing star formation, is still uncertain due to the fact that usual star formation rate (SFR) indicators – emission-line luminosities based on the assumption of photoionization by young stars – cannot be used for active galaxies as the ionizing source is the AGN. We thus investigate the use of SFR derived from the stellar population and its relation with that derived from the gas for a sample of 170 AGN hosts and a matched control sample of 291 galaxies. We compare the values of SFR densities obtained via the H α emission line ($\rm \Sigma SFR_{Gas}$) for regions ionized by hot stars according to diagnostic diagrams with those obtained from stellar population synthesis ($\rm \Sigma SFR_\star$) over the last 1 to 100 Myr. We find that the $\rm \Sigma SFR_\star$ over the last 20 Myr closely reproduces the $\rm \Sigma SFR_{Gas}$, although a better match is obtained via the transformation: $\mbox{log($ \rm \Sigma SFR_\star $)} = (0.872\pm 0.004)\mbox{log($\rm \Sigma SFR_{Gas}$)} -(0.075\pm 0.006)$ (or $\mbox{log($\rm \Sigma SFR_{Gas}$)} = (1.147\pm 0.005)\mbox{log($ \rm \Sigma SFR_\star $)} +(0.086\pm 0.080)$), which is valid for both AGN hosts and non-active galaxies. We also compare the reddening obtained via the gas H α/H β ratio with that derived via the full spectral fitting in the stellar population synthesis. We find that the ratio between the gas and stellar extinction is in the range 2.64 ≤AVg/AV⋆ ≤ 2.85, in approximate agreement with previous results from the literature, obtained for smaller samples. We interpret the difference as being due to the fact that the reddening of the stars is dominated by that affecting the less obscured underlying older population, while the reddening of the gas is larger as it is associated with a younger stellar population buried deeper in the dust.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3907
      Issue No: Vol. 501, No. 3 (2020)
  • Simulation-based inference of dynamical galaxy cluster masses with 3D
           convolutional neural networks
    • Authors: Kodi Ramanah D; Wojtak R, Arendse N.
      Pages: 4080 - 4091
      Abstract: ABSTRACTWe present a simulation-based inference framework using a convolutional neural network to infer dynamical masses of galaxy clusters from their observed 3D projected phase-space distribution, which consists of the projected galaxy positions in the sky and their line-of-sight velocities. By formulating the mass estimation problem within this simulation-based inference framework, we are able to quantify the uncertainties on the inferred masses in a straightforward and robust way. We generate a realistic mock catalogue emulating the Sloan Digital Sky Survey (SDSS) Legacy spectroscopic observations (the main galaxy sample) for redshifts z ≲ 0.09 and explicitly illustrate the challenges posed by interloper (non-member) galaxies for cluster mass estimation from actual observations. Our approach constitutes the first optimal machine learning-based exploitation of the information content of the full 3D projected phase-space distribution, including both the virialized and infall cluster regions, for the inference of dynamical cluster masses. We also present, for the first time, the application of a simulation-based inference machinery to obtain dynamical masses of around 800 galaxy clusters found in the SDSS Legacy Survey, and show that the resulting mass estimates are consistent with mass measurements from the literature.
      PubDate: Mon, 21 Dec 2020 00:00:00 GMT
      DOI: 10.1093/mnras/staa3922
      Issue No: Vol. 501, No. 3 (2020)
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