Showing papers in "Monthly Notices of the Royal Astronomical Society in 2020"

dynesty: a dynamic nested sampling package for estimating Bayesian posteriors and evidences

Abstract: We present dynesty, a public, open-source, Python package to estimate Bayesian posteriors and evidences (marginal likelihoods) using Dynamic Nested Sampling. By adaptively allocating samples based on posterior structure, Dynamic Nested Sampling has the benefits of Markov Chain Monte Carlo algorithms that focus exclusively on posterior estimation while retaining Nested Sampling's ability to estimate evidences and sample from complex, multi-modal distributions. We provide an overview of Nested Sampling, its extension to Dynamic Nested Sampling, the algorithmic challenges involved, and the various approaches taken to solve them. We then examine dynesty's performance on a variety of toy problems along with several astronomical applications. We find in particular problems dynesty can provide substantial improvements in sampling efficiency compared to popular MCMC approaches in the astronomical literature. More detailed statistical results related to Nested Sampling are also included in the Appendix.

H0LiCOW – XIII. A 2.4 per cent measurement of H0 from lensed quasars: 5.3σ tension between early- and late-Universe probes

Abstract: We present a measurement of the Hubble constant ($H_{0}$) and other cosmological parameters from a joint analysis of six gravitationally lensed quasars with measured time delays. All lenses except the first are analyzed blindly with respect to the cosmological parameters. In a flat $\Lambda$CDM cosmology, we find $H_{0} = 73.3_{-1.8}^{+1.7}$, a 2.4% precision measurement, in agreement with local measurements of $H_{0}$ from type Ia supernovae calibrated by the distance ladder, but in $3.1\sigma$ tension with $Planck$ observations of the cosmic microwave background (CMB). This method is completely independent of both the supernovae and CMB analyses. A combination of time-delay cosmography and the distance ladder results is in $5.3\sigma$ tension with $Planck$ CMB determinations of $H_{0}$ in flat $\Lambda$CDM. We compute Bayes factors to verify that all lenses give statistically consistent results, showing that we are not underestimating our uncertainties and are able to control our systematics. We explore extensions to flat $\Lambda$CDM using constraints from time-delay cosmography alone, as well as combinations with other cosmological probes, including CMB observations from $Planck$, baryon acoustic oscillations, and type Ia supernovae. Time-delay cosmography improves the precision of the other probes, demonstrating the strong complementarity. Allowing for spatial curvature does not resolve the tension with $Planck$. Using the distance constraints from time-delay cosmography to anchor the type Ia supernova distance scale, we reduce the sensitivity of our $H_0$ inference to cosmological model assumptions. For six different cosmological models, our combined inference on $H_{0}$ ranges from $\sim73$-$78~\mathrm{km~s^{-1}~Mpc^{-1}}$, which is consistent with the local distance ladder constraints.

Bayesian inference for compact binary coalescences with bilby: validation and application to the first LIGO–Virgo gravitational-wave transient catalogue

Abstract: Gravitational waves provide a unique tool for observational astronomy. While the first LIGO–Virgo catalogue of gravitational-wave transients (GWTC-1) contains 11 signals from black hole and neutron star binaries, the number of observations is increasing rapidly as detector sensitivity improves. To extract information from the observed signals, it is imperative to have fast, flexible, and scalable inference techniques. In a previous paper, we introduced bilby: a modular and user-friendly Bayesian inference library adapted to address the needs of gravitational-wave inference. In this work, we demonstrate that bilby produces reliable results for simulated gravitational-wave signals from compact binary mergers, and verify that it accurately reproduces results reported for the 11 GWTC-1 signals. Additionally, we provide configuration and output files for all analyses to allow for easy reproduction, modification, and future use. This work establishes that bilby is primed and ready to analyse the rapidly growing population of compact binary coalescence gravitational-wave signals.

The milky way total mass profile as inferred from Gaia DR2

Abstract: We determine the Milky Way (MW) mass profile inferred from fitting physically motivated models to the Gaia DR2 Galactic rotation curve and other data. Using various hydrodynamical simulations of MW-mass haloes, we show that the presence of baryons induces a contraction of the dark matter (DM) distribution in the inner regions, r . 20 kpc. We provide an analytic expression that relates the baryonic distribution to the change in the DM halo profile. For our galaxy, the contraction increases the enclosed DM halo mass by factors of roughly 1.3, 2 and 4 at radial distances of 20, 8 and 1 kpc, respectively compared to an uncontracted halo. Ignoring this contraction results in systematic biases in the inferred halo mass and concentration. We provide a best-fitting contracted NFW halo model to the MW rotation curve that matches the data very well†. The best-fit has a DM halo mass, MDM 200 = 0.97+0.24 −0.19×1012 M, and concentration before baryon contraction of 9.4 +1.9 −2.6 , which lie close to the median halo mass–concentration relation predicted in ΛCDM. The inferred total mass, Mtotal 200 = 1.08+0.20 −0.14 × 1012 M, is in good agreement with recent measurements. The model gives a MW stellar mass of 5.04+0.43 −0.52 × 1010 M and infers that the DM density at the Solar position is ρ DM = 8.8 +0.5 −0.5 ×10−3 M pc−3 ≡ 0.33+0.02 −0.02 GeV cm−3 . The rotation curve data can also be fitted with an uncontracted NFW halo model, but with very different DM and stellar parameters. The observations prefer the physically motivated contracted NFW halo, but the measurement uncertainties are too large to rule out the uncontracted NFW halo.

Unresolved stellar companions with Gaia DR2 astrometry

Abstract: For stars with unresolved companions, motions of the centre of light and that of mass decouple, causing a single-source astrometric model to perform poorly. We show that such stars can be easily detected with the reduced chi2 statistic, or RUWE, provided as part of Gaia DR2. We convert RUWE into the amplitude of the image centroid wobble, which, if scaled by the source distance, is proportional to the physical separation between companions (for periods up to several years). We test this idea on a sample of known spectroscopic binaries and demonstrate that the amplitude of the centroid perturbation scales with the binary period and the mass ratio as expected. We apply this technique to the Gaia DR2 data and show how the binary fraction evolves across the Hertzsprung--Russell diagram. The observed incidence of unresolved companions is high for massive young stars and drops steadily with stellar mass, reaching its lowest levels for white dwarfs. We highlight the elevated binary fraction for the nearby Blue Stragglers and Blue Horizontal Branch stars. We also illustrate how unresolved hierarchical triples inflate the relative velocity signal in wide binaries. Finally, we point out a hint of evidence for the existence of additional companions to the hosts of extrasolar hot jupiters.

The lifecycle of molecular clouds in nearby star-forming disc galaxies

Abstract: German Research Foundation (DFG) KR4801/1-1 German Research Foundation (DFG) KR4801/2-1 European Research Council (ERC) 714907 Australia-Germany Joint Research Cooperation Scheme (UA-DAAD) 57387355 Australian Research Council FT140101202 Programme National 'Physique et Chimie du Milieu Interstellaire' (PCMI) of the Centre national de la recherche scientifique/Institut national des sciences de l'Univers (CNRS/INSU) Institut de Chimie/Institut de Physique (INC/INP) French Atomic Energy Commission Centre National D'etudes Spatiales Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU INP Institut national de physique nucleaire et de physique des particules (IN2P3) French Atomic Energy Commission Centre National D'etudes Spatiales European Research Council (ERC) 694343 726384 National Science Foundation (NSF) 1615105 1615109 1653300 National Aeronautics and Space Administration (NASA) Astrophysics Data Analysis Program (ADAP) NNX16AF48G NNX17AF39G Natural Sciences and Engineering Research Council of Canada RGPIN-2017-03987 Fondo de Fomento al Desarrollo Cientifico y Tecnologico of the Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT/FONDECYT), Programa de Iniciacion, Folio 11150220 German Research Foundation (DFG) SFB 881 Germany's Excellence Strategy (Heidelberg STRUCTURES Excellence Cluster) EXC-2181/1-390900948 German Research Foundation (DFG) KR4598/2-1 MINECO/FEDER AYA2016-79006-P MCIU/AEI/FEDER PGC2018-094671-B-I00 Centre National de la Recherche Scientifique (CNRS) Max Planck Society IGN (Spain)

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey : measurement of the BAO and growth rate of structure of the luminous red galaxy sample from the anisotropic power spectrum between redshifts 0.6 and 1.0

Abstract: We present the large-scale clustering of emission line galaxies (ELG) from the Data Release 16 of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey. The ELG sample contains 173,736 galaxies covering 1,170 square degrees in the redshift range $0.6 < z < 1.1$. We perform a BAO measurement from the post-reconstruction power spectrum monopole, and study redshift space distortions (RSD) in the first three multipoles. Purely angular photometric systematics are mitigated by nulling angular signal in pixels of appropriate size. Variations of the redshift distribution with photometric conditions are accounted for by splitting and measuring the radial selection function of the survey in regions of homogeneous imaging. Both techniques result in integral constraints which we model consistently. At the effective redshift $z_{\rm eff} = 0.845$ we measure $D_{\rm V}(z_{\rm eff})/r_{\rm drag} = 18.33_{-0.62}^{+0.57}$, with $D_{\rm V}$ the volume averaged distance and $r_{\rm drag}$ the comoving sound horizon at the drag epoch. In combination with the RSD measurement, at $z_{\rm eff} = 0.85$ we find $f\sigma_8(z_{\rm eff}) = 0.289_{-0.096}^{+0.085}$, with $f$ the growth rate of structure and $\sigma_8$ the normalisation of the linear power spectrum, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 20.0_{-2.2}^{+2.4}$ and $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 19.17 \pm 0.99$ with $D_{\rm H}$ and $D_{\rm M}$ the Hubble and comoving angular distances, respectively. Quoted errors include statistical and systematic contributions. We find good agreement with the results obtained in configuration space, thus allowing a consensus measurement of $f\sigma_8(z_{\rm eff}) = 0.315 \pm 0.095$, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 19.6_{-2.1}^{+2.2}$ and $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 19.5 \pm 1.0$. This measurement is in agreement with a flat $\Lambda$CDM model with Planck parameters.

Warm dark matter chills out: constraints on the halo mass function and the free-streaming length of dark matter with eight quadruple-image strong gravitational lenses

Abstract: The free-streaming length of dark matter depends on fundamental dark matter physics, and determines the abundance and concentration of dark matter halos on sub-galactic scales. Using the image positions and flux ratios from eight quadruply-imaged quasars, we constrain the free-streaming length of dark matter and the amplitude of the subhalo mass function (SHMF). We model both main deflector subhalos and halos along the line of sight, and account for warm dark matter (WDM) free-streaming effects on the mass function and mass-concentration relation. By calibrating the scaling of the SHMF with host halo mass and redshift using a suite of simulated halos, we infer a global normalization for the SHMF. We account for finite-size background sources, and marginalize over the mass profile of the main deflector. Parameterizing dark matter free-streaming through the half-mode mass $m_{\rm{hm}}$, we constrain the thermal relic particle mass $m_{\rm{DM}}$ corresponding to $m_{\rm{hm}}$. At $95 \%$ CI: $m_{\rm{hm}} 5.2 \ \rm{keV}$). We disfavor $m_{\rm{DM}} = 4.0 \rm{keV}$ and $ m_{\rm{DM}} = 3.0 \rm{keV}$ with likelihood ratios of 7:1 and 30:1, respectively, relative to the peak of the posterior distribution. Assuming cold dark matter, we constrain the projected mass in substructure between $10^6 - 10^{9} M_{\odot}$ near lensed images. At $68 \%$ CI, we infer $2.0 - 6.1 \times 10^{7} M_{\odot} \rm{kpc^{-2}}$, corresponding to mean projected mass fraction $\bar{f}_{\rm{sub}} = 0.035_{-0.017}^{+0.021}$. At $95 \%$ CI, we obtain a lower bound on the projected mass of $0.6 \times 10^{7} M_{\odot} \rm{kpc^{-2}}$, corresponding to $\bar{f}_{\rm{sub}} > 0.005$. These results agree with the predictions of cold dark matter.

The overarching framework of core-collapse supernova explosions as revealed by 3D fornax simulations

Abstract: We have conducted nineteen state-of-the-art 3D core-collapse supernova simulations spanning a broad range of progenitor masses. This is the largest collection of sophisticated 3D supernova simulations ever performed. We have found that while the majority of these models explode, not all do, and that even models in the middle of the available progenitor mass range may be less explodable. This does not mean that those models for which we did not witness explosion would not explode in Nature, but that they are less prone to explosion than others. One consequence is that the "compactness" measure is not a metric for explodability. We find that lower-mass massive star progenitors likely experience lower-energy explosions, while the higher-mass massive stars likely experience higher-energy explosions. Moreover, most 3D explosions have a dominant dipole morphology, have a pinched, wasp-waist structure, and experience simultaneous accretion and explosion. We reproduce the general range of residual neutron-star masses inferred for the galactic neutron-star population. The most massive progenitor models, however, in particular vis a vis explosion energy, need to be continued for longer physical times to asymptote to their final states. We find that while the majority of the inner ejecta have Y$_e = 0.5$, there is a substantial proton-rich tail. This result has important implications for the nucleosynthetic yields as a function of progenitor. Finally, we find that the non-exploding models eventually evolve into compact inner configurations that experience a quasi-periodic spiral SASI mode. We otherwise see little evidence of the SASI in the exploding models.

STRIDES : a 3.9 per cent measurement of the Hubble constant from the strong lens system DES J0408−5354

Abstract: We present a blind time-delay cosmographic analysis for the lens system DES J0408−5354. This system is extraordinary for the presence of two sets of multiple images at different redshifts, which provide the opportunity to obtain more information at the cost of increased modelling complexity with respect to previously analysed systems. We perform detailed modelling of the mass distribution for this lens system using three band Hubble Space Telescope imaging. We combine the measured time delays, line-of-sight central velocity dispersion of the deflector, and statistically constrained external convergence with our lens models to estimate two cosmological distances. We measure the ‘effective’ time-delay distance corresponding to the redshifts of the deflector and the lensed quasar DeffΔt=3382+146−115 Mpc and the angular diameter distance to the deflector Dd = 1711+376−280 Mpc, with covariance between the two distances. From these constraints on the cosmological distances, we infer the Hubble constant H0= 74.2+2.7−3.0 km s−1 Mpc−1 assuming a flat ΛCDM cosmology and a uniform prior for Ωm as Ωm∼U(0.05,0.5)⁠. This measurement gives the most precise constraint on H0 to date from a single lens. Our measurement is consistent with that obtained from the previous sample of six lenses analysed by the H0 Lenses in COSMOGRAIL’s Wellspring (H0LiCOW) collaboration. It is also consistent with measurements of H0 based on the local distance ladder, reinforcing the tension with the inference from early Universe probes, for example, with 2.2σ discrepancy from the cosmic microwave background measurement.

Possible periodic activity in the repeating FRB 121102

Abstract: The discovery that at least some Fast Radio Bursts (FRBs) repeat has ruled out cataclysmic events as the progenitors of these particular bursts. FRB~121102 is the most well-studied repeating FRB but despite extensive monitoring of the source, no underlying pattern in the repetition has previously been identified. Here, we present the results from a radio monitoring campaign of FRB~121102 using the 76-m Lovell telescope. Using the pulses detected in the Lovell data along with pulses from the literature, we report a detection of periodic behaviour of the source over the span of five years of data. We predict that the source is currently `off' and that it should turn `on' for the approximate MJD range $59002-59089$ (2020-06-02 to 2020-08-28). This result, along with the recent detection of periodicity from another repeating FRB, highlights the need for long-term monitoring of repeating FRBs at a high cadence. Using simulations, we show that one needs at least 100 hours of telescope time to follow-up repeating FRBs at a cadence of 0.5--3 days to detect periodicities in the range of 10--150 days. If the period is real, it shows that repeating FRBs can have a large range in their activity periods that might be difficult to reconcile with neutron star precession models.

The biggest splash

Abstract: Using a large sample of bright nearby stars with accurate Gaia Data Release 2 astrometry and auxiliary spectroscopy we map out the properties of the principle Galactic components such as the “thin” and “thick” discs and the halo. We confirm previous claims that in the Solar neighborhood, there exists a large population of metal-rich ([Fe/H]>−0.7) stars on highly eccentric orbits. By studying the evolution of elemental abundances, kinematics and stellar ages in the plane of azimuthal velocity vφ and metallicity [Fe/H], we demonstrate that this metal-rich halo-like component, which we dub the Splash, is linked to the α-rich (or “thick”) disc. Splash stars have little to no angular momentum and many are on retrograde orbits. They are predominantly old, but not as old as the stars deposited into the Milky Way in the last major merger. We argue, in agreement with several recent studies, that the Splash stars may have been born in the Milky Way's proto-disc prior to the massive ancient accretion event which drastically altered their orbits. We can not, however, rule out other (alternative) formation channels. Taking advantage of the causal connection between the merger and the Splash, we put constraints of the epoch of the last massive accretion event to have finished 9.5 Gyr ago. The link between the local metal-rich and metal-poor retrograde stars is confirmed using a large suite of cutting-edge numerical simulations of the Milky Way's formation.

Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR

Abstract: A new upper limit on the 21 cm signal power spectrum at a redshift of z approximate to 9.1 is presented, based on 141 h of data obtained with the Low-Frequency Array (LOFAR). The analysis includes significant improvements in spectrally smooth gain-calibration, Gaussian Process Regression (GPR) foreground mitigation and optimally weighted power spectrum inference. Previously seen 'excess power' due to spectral structure in the gain solutions has markedly reduced but some excess power still remains with a spectral correlation distinct from thermal noise. This excess has a spectral coherence scale of 0.25-0.45 MHz and is partially correlated between nights, especially in the foreground wedge region. The correlation is stronger between nights covering similar local sidereal times. A best 2-sigma upper limit of Delta(2)(21) <(73)(2) mK(2) at k = 0.075 h cMpc(-1) is found, an improvement by a factor approximate to 8 in power compared to the previously reported upper limit. The remaining excess power could be due to residual foreground emission from sources or diffuse emission far away from the phase centre, polarization leakage, chromatic calibration errors, ionosphere, or low-level radiofrequency interference. We discuss future improvements to the signal processing chain that can further reduce or even eliminate these causes of excess power.

A unified picture of Galactic and cosmological fast radio bursts

Abstract: The discovery of a fast radio burst (FRB) in our galaxy associated with a magnetar (neutron star with strong magnetic field) has provided a critical piece of information to help us finally understand these enigmatic transients. We show that the volumetric rate of Galactic-FRB like events is consistent with the faint end of the cosmological FRB rate, and hence they most likely belong to the same class of transients. The Galactic FRB had an accompanying X-ray burst but many X-ray bursts from the same object had no radio counterpart. Their relative rates suggest that for every FRB there are roughly 100 to 1000 X-ray bursts. The radio lightcurve of the galactic FRB had two spikes separated by 30 ms in the 400-800 MHz frequency band. This is an important clue and highly constraining of the class of models where the radio emission is produced outside the light-cylinder of the magnetar. We suggest that magnetic disturbances close to the magnetar surface propagate to a distance of a few tens of neutron star radii where they damp and produce radio emission. The coincident hard X-ray spikes associated with the two FRB pulses seen in this burst and the flux ratio between the two frequency bands can be understood in this scenario. This model provides a unified picture for faint bursts like the Galactic FRB as well as the bright events seen at cosmological distances.

An ALMA survey of the SCUBA-2 CLS UDS field: physical properties of 707 sub-millimetre galaxies

Abstract: We analyse the physical properties of a large, homogeneously selected sample of ALMA-located sub-mm galaxies (SMGs) detected in the SCUBA-2 CLS 850-$\mu$m map of the UKIDSS/UDS field. This survey, AS2UDS, identified 707 SMGs across the ~1 sq.deg. field, including ~17 per cent which are undetected in the optical/near-infrared to $K$>~25.7 mag. We interpret the UV-to-radio data using a physically motivated model, MAGPHYS and determine a median photometric redshift of z=2.61+-0.08, with a 68th percentile range of z=1.8-3.4 and just ~6 per cent at z>4. The redshift distribution is well fit by a model combining evolution of the gas fraction in halos with the growth of halo mass past a threshold of ~4x10$^{12}$M$_\odot$, thus SMGs may represent the highly efficient collapse of gas-rich massive halos. Our survey provides a sample of the most massive, dusty galaxies at z>~1, with median dust and stellar masses of $M_d$=(6.8+-0.3)x10$^{8}$M$_\odot$ (thus, gas masses of ~10$^{11}$M$_\odot$) and $M_\ast=$(1.26+-0.05)x10$^{11}$M$_\odot$. These galaxies have gas fractions of $f_{gas}=$0.41+-0.02 with depletion timescales of ~150Myr. The gas mass function evolution at high masses is consistent with constraints at lower masses from blind CO-surveys, with an increase to z~2-3 and then a decline at higher redshifts. The space density and masses of SMGs suggests that almost all galaxies with $M_\ast$>~2x10$^{11}$M$_\odot$ have passed through an SMG-like phase. We find no evolution in dust temperature at a constant far-infrared luminosity across z~1.5-4. We show that SMGs appear to behave as simple homologous systems in the far-infrared, having properties consistent with a centrally illuminated starburst. Our study provides strong support for an evolutionary link between the active, gas-rich SMG population at z>1 and the formation of massive, bulge-dominated galaxies across the history of the Universe.

The completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: BAO and RSD measurements from anisotropic clustering analysis of the quasar sample in configuration space between redshift 0.8 and 2.2

Abstract: We measure the anisotropic clustering of the quasar sample from Data Release 16 (DR16) of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey (eBOSS). A sample of $343,708$ spectroscopically confirmed quasars between redshift $0.8

Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations

Abstract: Globular clusters (GCs) formed when the Milky Way experienced a phase of rapid assembly. We use the wealth of information contained in the Galactic GC population to quantify the properties of the satellite galaxies from which the Milky Way assembled. To achieve this, we train an artificial neural network on the E-MOSAICS cosmological simulations of the co-formation and co-evolution of GCs and their host galaxies. The network uses the ages, metallicities, and orbital properties of GCs that formed in the same progenitor galaxies to predict the stellar masses and accretion redshifts of these progenitors. We apply the network to Galactic GCs associated with five progenitors: {\it Gaia}-Enceladus, the Helmi streams, Sequoia, Sagittarius, and the recently discovered, `low-energy' GCs, which provide an excellent match to the predicted properties of the enigmatic galaxy `Kraken'. The five galaxies cover a narrow stellar mass range [$M_\star=(0.6{-}4.6)\times10^8~{\rm M}_\odot$], but have widely different accretion redshifts ($z_{\rm acc}=0.57{-}2.65$). All accretion events represent minor mergers, but Kraken likely represents the most major merger ever experienced by the Milky Way, with stellar and virial mass ratios of $r_{M_\star}=1$:$31^{+34}_{-16}$ and $r_{M_{\rm h}}=1$:$7^{+4}_{-2}$, respectively. The progenitors match the $z=0$ relation between GC number and halo virial mass, but have elevated specific frequencies, suggesting an evolution with redshift. Even though these progenitors likely were the Milky Way's most massive accretion events, they contributed a total mass of only $\log{(M_{\rm \star,tot}/{\rm M}_\odot)}=9.0\pm0.1$, similar to the stellar halo. This implies that the Milky Way grew its stellar mass mostly by in-situ star formation. We conclude by organising these accretion events into the most detailed reconstruction to date of the Milky Way's merger tree.

The mass–metallicity and the fundamental metallicity relation revisited on a fully Te-based abundance scale for galaxies

Abstract: The relationships between stellar mass, gas-phase metallicity and star formation rate (i.e. the Mass-Metallicity, MZR, and the Fundamental Metallcity Relation, FMR) in the local Universe are revisited by fully anchoring the metallicity determination for SDSS galaxies on the Te abundance scale defined exploiting the strong-line metallicity calibrations presented in Curti et al. (2017). Self-consistent metallicity measurements allow a more unbiased assessment of the scaling relations involving M, Z and SFR, which provide powerful constraints for the chemical evolution models. We parametrise the MZR with a new functional form which allows us to better characterise the turnover mass. The slope and saturation metallicity are in good agreement with previous determinations of the MZR based on the Te method, while showing significantly lower normalisation compared to those based on photoionisation models. The Z- SFR dependence at fixed stellar mass is also investigated, being particularly evident for highly star forming galaxies, where the scatter in metallicity is reduced up to a factor of ~30%. A new parametrisation of the FMR is given by explicitly introducing the SFR-dependence of the turnover mass into the MZR. The residual scatter in metallicity for the global galaxy population around the new FMR is 0.054 dex. The new FMR presented in this work represents a useful local benchmark to compare theoretical predictions and observational studies (of both local and high-redshift galaxies) whose metallicity measurements are tied to the abundance scale defined by the Te method, hence allowing to properly assess its evolution with cosmic time.

The bolometric quasar luminosity function at z = 0–7

Abstract: In this paper, we provide updated constraints on the bolometric quasar luminosity function (QLF) from 푧 = 0 to 푧 = 7. The constraints are based on an observational compilation that includes observations in the rest-frame IR, B band, UV, soft and hard X-ray in past decades. Our method follows Hopkins et al. 2007 with an updated quasar SED model and bolometric and extinction corrections. The new best-fit bolometric quasar luminosity function behaves qualitatively different from the Hopkins et al. 2007 model at high redshift. Compared with the old model, the number density normalization decreases towards higher redshift and the bright-end slope is steeper at 푧 & 2. Due to the paucity of measurements at the faint end, the faint end slope at 푧 & 5 is quite uncertain. We present two models, one featuring a progressively steeper faint-end slope at higher redshift and the other featuring a shallow faint-end slope at 푧 & 5. Further multi-band observations of the faint-end QLF are needed to distinguish between these models. The evolutionary pattern of the bolometric QLF can be interpreted as an early phase likely dominated by the hierarchical assembly of structures and a late phase likely dominated by the quenching of galaxies. We explore the implications of this model on the ionizing photon production by quasars, the CXB spectrum, the SMBH mass density and mass functions. The predicted hydrogen photoionization rate contributed by quasars is subdominant during the epoch of reionization and only becomes important at 푧 . 3. The predicted CXB spectrum, cosmic SMBH mass density and SMBH mass function are generally consistent with existing observations.

SHARP – VII. New constraints on the dark matter free-streaming properties and substructure abundance from gravitationally lensed quasars

Abstract: We present an analysis of seven strongly gravitationally lensed quasars and the corresponding constraints on the properties of dark matter. Our results are derived by modelling the lensed image positions and flux- ratios using a combination of smooth macro models and a population of low-mass haloes within the mass range 106 to 109 M☉. Our lens models explicitly include higher-order complexity in the form of stellar discs and luminous satellites, as well as low-mass haloes located along the observed lines of sight for the first time. Assuming a Cold Dark Matter (CDM) cosmology, we infer an average total mass fraction in substructure of f_sub = 0.012^{+0.007}_{-0.004} (68 per cent confidence limits), which is in agreement with the predictions from CDM hydrodynamical simulations to within 1σ. This result is closer to the predictions than those from previous studies that did not include line-of-sight haloes. Under the assumption of a thermal relic dark matter model, we derive a lower limit on the particle relic mass of mth > 5.58 keV (95 per cent confidence limits), which is consistent with a value of mth > 5.3 keV from the recent analysis of the Lyα forest. We also identify two main sources of possible systematic errors and conclude that deeper investigations in the complex structure of lens galaxies as well as the size of the background sources should be a priority for this field.

The relationship between black hole mass and galaxy properties: Examining the black hole feedback model in IllustrisTNG

Abstract: Supermassive black hole feedback is thought to be responsible for the lack of star formation, or quiescence, in a significant fraction of galaxies. We explore how observable correlations between the specific star formation rate (sSFR), stellar mass (M$_{\rm{star}}$), and black hole mass (M$_{\rm{BH}}$) are sensitive to the physics of black hole feedback in a galaxy formation model. We use the IllustrisTNG simulation suite, specifically the TNG100 simulation and ten model variations that alter the parameters of the black hole model. Focusing on central galaxies at $z = 0$ with M$_{\rm{star}} > 10^{10}$ M$_{\odot}$, we find that the sSFR of galaxies in IllustrisTNG decreases once the energy from black hole kinetic winds at low accretion rates becomes larger than the gravitational binding energy of gas within the galaxy stellar radius. This occurs at a particular M$_{\rm{BH}}$ threshold above which galaxies are found to sharply transition from being mostly star-forming to mostly quiescent. As a result of this behavior, the fraction of quiescent galaxies as a function of M$_{\rm{star}}$ is sensitive to both the normalization of the M$_{\rm{BH}}$-M$_{\rm{star}}$ relation and the M$_{\rm{BH}}$ threshold for quiescence in IllustrisTNG. Finally, we compare these model results to observations of 91 central galaxies with dynamical M$_{\rm{BH}}$ measurements with the caveat that this sample is not representative of the whole galaxy population. While IllustrisTNG reproduces the observed trend that quiescent galaxies host more massive black holes, the observations exhibit a broader scatter in M$_{\rm{BH}}$ at a given M$_{\rm{star}}$ and show a smoother decline in sSFR with M$_{\rm{BH}}$.

A lower bound on the maximum mass if the secondary in GW190814 was once a rapidly spinning neutron star

Abstract: The recent detection of GW190814 featured the merger of a binary with a primary having a mass of |$\sim 23\, \mathrm{ M}_{\odot }$| and a secondary with a mass of |$\sim 26\, \mathrm{ M}_{\odot }$|⁠ While the primary was most likely a black hole, the secondary could be interpreted as either the lightest black hole or the most massive neutron star ever observed, but also as the indication of a novel class of exotic compact objects We here argue that although the secondary in GW190814 is most likely a black hole at merger, it needs not be an ab-initio black hole nor an exotic object Rather, based on our current understanding of the nuclear-matter equation of state, it can be a rapidly rotating neutron star that collapsed to a rotating black hole at some point before merger Using universal relations connecting the masses and spins of uniformly rotating neutron stars, we estimate the spin, |$049_{-005}^{+008} \lesssim \chi \lesssim 068_{-005}^{+011}$|⁠, of the secondary – a quantity not constrained so far by the detection – and a novel strict lower bound on the maximum mass, |$M_{_{\mathrm{TOV}}}\gt 208^{+004}_{-004}\, \, \mathrm{ M}_{\odot }$| and an optimal bound of |$M_{_{\mathrm{TOV}}}\gt 215^{+004}_{-004}\, \, \mathrm{ M}_{\odot }$|⁠, of non-rotating neutron stars, consistent with recent observations of a very massive pulsar The new lower bound also remains valid even in the less likely scenario in which the secondary neutron star never collapsed to a black hole

Systematic opacity calculations for kilonovae

Abstract: Coalescence of neutron stars gives rise to kilonova, thermal emission powered by radioactive decays of freshly synthesized r-process nuclei. Although observational properties are largely affected by bound-bound opacities of r-process elements, available atomic data have been limited. In this paper, we study element-to-element variation of the opacities in the ejecta of neutron star mergers by performing systematic atomic structure calculations of r-process elements for the first time. We show that the distributions of energy levels tend to be higher as electron occupation increases for each electron shell due to the larger energy spacing caused by larger effects of spin-orbit and electron-electron interactions. As a result, elements with a fewer number of electrons in the outermost shells tend to give larger contributions to the bound-bound opacities. This implies that Fe is not representative for the opacities of light r-process elements. The average opacities for the mixture of r-process elements are found to be kappa ~ 20-30 cm^2 g^{-1} for the electron fraction of Ye ~ 0.25, with no lanthanide) are needed to explain the early, blue emission in GW170817/AT2017gfo while lanthanide-rich ejecta (with a mass fraction of lanthanides ~ 5 x 10^{-3}) reproduce the long-lasting near-infrared emission.

Detection of Fe i in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy

Abstract: High-resolution Doppler-resolved spectroscopy has opened up a new window into the atmospheres of both transiting and non-transiting exoplanets. Here, we present VLT/UVES observations of a transit of WASP-121b, an 'ultra-hot' Jupiter previously found to exhibit a temperature inversion and detections of multiple species at optical wavelengths. We present initial results using the blue arm of UVES ($\approx$3700-5000A), recovering a clear signal of neutral Fe in the planet's atmosphere at >8$\sigma$, which could contribute to (or even fully explain) the temperature inversion in the stratosphere. However, using standard cross-correlation methods, it is difficult to extract physical parameters such as temperature and abundances. Recent pioneering efforts have sought to develop likelihood `mappings' that can be used to directly fit models to high-resolution datasets. We introduce a new framework that directly computes the likelihood of the model fit to the data, and can be used to explore the posterior distribution of parameterised model atmospheres via MCMC techniques. Our method also recovers the physical extent of the atmosphere, as well as account for time- and wavelength-dependent uncertainties. We measure a temperature of $3710^{+490}_{-510}$K, indicating a higher temperature in the upper atmosphere when compared to low-resolution observations. We also show that the Fe I signal is physically separated from the exospheric Fe II. However, the temperature measurements are highly degenerate with aerosol properties; detection of additional species, using more sophisticated atmospheric models, or combining these methods with low-resolution spectra should help break these degeneracies.

x-cigale: fitting AGN/galaxy SEDs from X-ray to infrared

Abstract: CIGALE is a powerful multiwavelength spectral energy distribution (SED) fitting code for extragalactic studies. However, the current version of CIGALE is not able to fit X-ray data, which often provide unique insights into AGN intrinsic power. We develop a new X-ray module for CIGALE, allowing it to fit SEDs from the X-ray to infrared (IR). We also improve the AGN fitting of CIGALE from UV-to-IR wavelengths. We implement a modern clumpy two-phase torus model, SKIRTOR. To account for moderately extincted type 1 AGNs, we implement polar-dust extinction. We publicly release the source code (named X-CIGALE). We test X-CIGALE with X-ray detected AGNs in SDSS, COSMOS, and AKARI-NEP. The fitting quality (as indicated by reduced $\chi^2$) is good in general, indicating that X-CIGALE is capable of modelling the observed SED from X-ray to IR. We discuss constrainability and degeneracy of model parameters in the fitting of AKARI-NEP, for which excellent mid-IR photometric coverage is available. We also test fitting a sample of AKARI-NEP galaxies for which only X-ray upper limits are available from Chandra observations, and find that the upper limit can effectively constrain the AGN SED contribution for some systems. Finally, using X-CIGALE, we assess the ability of Athena to constrain the AGN activity in future extragalactic studies.

Signatures of the core-powered mass-loss mechanism in the exoplanet population: dependence on stellar properties and observational predictions

Abstract: Recent studies have shown that atmospheric mass-loss powered by the cooling luminosity of a planet's core can explain the observed radius valley separating super-Earths and sub-Neptunes, even without photoevaporation. In this work, we investigate the dependence of this core-powered mass-loss mechanism on stellar mass ($M_\ast$), metallicity ($Z_\ast$) and age ($\tau_\ast$). Without making any changes to the underlying planet population, we find that the core-powered mass-loss model yields a shift in the radius valley to larger planet sizes around more massive stars with a slope given by $\text{d log}R_p/\text{d log}M_\ast \simeq 0.35$, in agreement with observations. To first order, this slope is driven by the dependence of core-powered mass-loss on the bolometric luminosity of the host star and is given by $\text{d log}R_p/\text{d log}M_\ast \simeq (3\alpha-2)/36 \simeq 0.33$, where $(L_\ast/L_\odot) = (M_\ast/M_\odot)^\alpha$ is the stellar mass-luminosity relation and $\alpha\simeq 4.6$ for the CKS dataset. We therefore find, in contrast to photoevaporation models, no evidence for a linear correlation between planet and stellar mass, but can't rule it out either. In addition, we show that the location of the radius valley is, to first order, independent of stellar age and metallicity. Since core-powered mass-loss proceeds over Gyr timescales, the abundance of super-Earths relative to sub-Neptunes increases with age but decreases with stellar metallicity. Finally, due the dependence of the envelope's cooling timescale on metallicity, we find that the radii of sub-Neptunes increase with metallicity and decrease with age with slopes given by $\text{d log}R_p/\text{d log}Z_\ast \simeq 0.1$ and $\text{d log}R_p/\text{d log}\tau_\ast \simeq -0.1$, respectively. We conclude with a series of observational tests that can differentiate between core-powered mass-loss and photoevaporation models.

SuperNNova: an open-source framework for Bayesian, Neural Network based supernova classification

Abstract: We introduce SuperNNova, an open source supernova photometric classification framework which leverages recent advances in deep neural networks. Our core algorithm is a recurrent neural network (RNN) that is trained to classify light-curves using photometric information only. Additional information such as host-galaxy redshift can be incorporated to improve performance. We evaluate our framework using realistic supernovae simulations that include survey detection. We show that our method, for the type Ia vs. non Ia supernovae classification problem, reaches accuracies greater than 96.92 +- 0.09 without any redshift information and up to 99.55 +- 0.06 when redshift, either photometric or spectroscopic, is available. Further, we show that our method attains unprecedented performance for classification of incomplete light-curves, reaching accuracies >86.4 +- 0.1 (>93.5 +- 0.8) without host-galaxy redshift (with redshift information) two days before maximum light. In contrast with previous methods, there is no need for time-consuming feature engineering and we show that our method scales to very large datasets with a modest computing budget. In addition, we investigate often neglected pitfalls of machine learning algorithms. We show that commonly used algorithms suffer from poor calibration and overconfidence on out-of-distribution samples when applied to supernovae data. We devise extensive tests to estimate the robustness of classifiers and cast the learning procedure under a Bayesian light, demonstrating a much better handling of uncertainties. We study the benefits of Bayesian RNNs for SN Ia cosmology. Our code is open-sourced and available on https://github.com/supernnova/SuperNNova.

Binary black holes in the pair instability mass gap

Abstract: Pair instability (PI) and pulsational PI prevent the formation of black holes (BHs) with mass $\gtrsim{}60$ M$_\odot$ from single star evolution. Here, we investigate the possibility that BHs with mass in the PI gap form via stellar mergers and multiple stellar mergers, facilitated by dynamical encounters in young star clusters. We analyze $10^4$ simulations, run with the direct N-body code nbody6++gpu coupled with the population synthesis code MOBSE. We find that up to $\sim{}6$~% of all simulated BHs have mass in the PI gap, depending on progenitor's metallicity. This formation channel is strongly suppressed in metal-rich (Z = 0.02) star clusters, because of stellar winds. BHs with mass in the PI gap are initially single BHs but can efficiently acquire companions through dynamical exchanges. We find that $\sim{}$21%, 10% and 0.5% of all binary BHs have at least one component in the PI mass gap at metallicity Z = 0.0002, 0.002 and 0.02, respectively. Based on the evolution of the cosmic star formation rate and metallicity, and under the assumption that all stars form in young star clusters, we predict that $\sim{}5$~% of all binary BH mergers detectable by advanced LIGO and Virgo at their design sensitivity have at least one component in the PI mass gap.

A cosmic UV/X-ray background model update

Abstract: We present an updated model of the cosmic ionizing background from the UV to the X-rays. Relative to our previous model (Faucher-Giguere et al. 2009), the new model provides a better match to a large number of up-to-date empirical constraints, including: 1) new galaxy and AGN luminosity functions; 2) stellar spectra including binary stars; 3) obscured and unobscured AGN; 4) a measurement of the non-ionizing UV background; 5) measurements of the intergalactic HI and HeII photoionization rates at z~0-6; 6) the local X-ray background; and 7) improved measurements of the intergalactic opacity. In this model, AGN dominate the HI ionizing background at z<~3 and star-forming galaxies dominate it at higher redshifts. Combined with the steeply declining AGN luminosity function beyond z~2, the slow evolution of the HI ionization rate inferred from the high-redshift HI Lya forest requires an escape fraction from star-forming galaxies that increases with redshift (a population-averaged escape fraction of ~1% suffices to ionize the intergalactic medium at z=3 when including the contribution from AGN). We provide effective photoionization and photoheating rates calibrated to match the Planck 2018 reionization optical depth and recent constraints from the HeII Lya forest in hydrodynamic simulations.

Massively parallel Bayesian inference for transient gravitational-wave astronomy

Abstract: Understanding the properties of transient gravitational waves (GWs) and their sources is of broad interest in physics and astronomy. Bayesian inference is the standard framework for astrophysical measurement in transient GW astronomy. Usually, stochastic sampling algorithms are used to estimate posterior probability distributions over the parameter spaces of models describing experimental data. The most physically accurate models typically come with a large computational overhead which can render data analsis extremely time consuming, or possibly even prohibitive. In some cases highly specialized optimizations can mitigate these issues, though they can be difficult to implement, as well as to generalize to arbitrary models of the data. Here, we investigate an accurate, flexible, and scalable method for astrophysical inference: parallelized nested sampling. The reduction in the wall-time of inference scales almost linearly with the number of parallel processes running on a high-performance computing cluster. By utilizing a pool of several hundreds or thousands of CPUs in a high-performance cluster, the large wall times of many astrophysical inferences can be alleviated while simultaneously ensuring that any GW signal model can be used ‘out of the box’, i.e. without additional optimization or approximation. Our method will be useful to both the LIGO-Virgo-KAGRA collaborations and the wider scientific community performing astrophysical analyses on GWs. An implementation is available in the open source gravitational-wave inference library pBilby (parallel bilby).