The 100 most-cited articles in Monthly Notices of the Royal Astronomical Society, 2018

The distribution of elements in galaxies provides a wealth of information about their production sites and their subsequent mixing into the interstellar medium. Here we investigate the elemental distributions of stars in the IllustrisTNG simulations. We analyse the abundance ratios of magnesium and europium in Milky Way-like galaxies from the TNG100 simulation (stellar masses log (M⋆/M⊙) ∼ 9.7–11.2). Comparison of observed magnesium and europium for individual stars in the Milky Way with the stellar abundances in our more than 850 Milky Way-like galaxies provides stringent constraints on our chemical evolutionary methods. Here, we use the magnesium-to-iron ratio as a proxy for the effects of our SNII (core-collapse supernovae) and SNIa (Type Ia supernovae) metal return prescription and as a comparison to a variety of galactic observations. The europium-to-iron ratio tracks the rare ejecta from neutron star–neutron star mergers, the assumed primary site of europium production in our models, and is a sensitive probe of the effects of metal diffusion within the gas in our simulations.…

The Feedback In Realistic Environments (FIRE) project explores feedback in cosmological galaxy formation simulations.Previous FIRE simulations used an identical source code ('FIRE-1') for consistency.Motivated by the development of more accurate numerics -including hydrodynamic solvers, gravitational softening, and supernova coupling algorithmsand exploration of new physics (e.g.magnetic fields), we introduce 'FIRE-2', an updated numerical implementation of FIRE physics for the GIZMO code.We run a suite of simulations and compare against FIRE-1: overall, FIRE-2 improvements do not qualitatively change galaxy-scale properties.We pursue an extensive study of numerics versus physics.Details of the star formation algorithm, cooling physics, and chemistry have weak effects provided that we include metal-line cooling and star formation occurs at higher-than-mean densities.We present new resolution criteria for high-resolution galaxy simulations.Most galaxy-scale properties are robust to numerics we test, provided: (1) Toomre masses are resolved; (2) feedback coupling ensures conservation,…

We introduce the IllustrisTNG project, a new suite of cosmological magnetohydrodynamical simulations performed with the moving-mesh code AREPO employing an updated Illustris galaxy formation model. Here we focus on the general properties of magnetic fields and the diffuse radio emission in galaxy clusters. Magnetic fields are prevalent in galaxies, and their build-up is closely linked to structure formation. We find that structure formation amplifies the initial seed fields ($10^{-14}$ comoving Gauss) to the values observed in low-redshift galaxies ($1-10\,μ{\rm G}$). The magnetic field topology is closely connected to galaxy morphology such that irregular fields are hosted by early-type galaxies, while large-scale, ordered fields are present in disc galaxies. Using two simple models for the energy distribution of relativistic electrons we predict the diffuse radio emission of $280$ clusters with a baryonic mass resolution of $1.1\times 10^{7}\,{\rm M_{\odot}}$, and generate mock observations for VLA, LOFAR, ASKAP and SKA. Our simulated clusters show extended radio emission, whose…

Using a large sample of main sequence stars with 7D measurements supplied by Gaia and SDSS, we study the kinematic properties of the local (within ∼10 kpc from the Sun) stellar halo. We demonstrate that the halo’s velocity ellipsoid evolves strongly with metallicity. At the low-[Fe/H] end, the orbital anisotropy (the amount of motion in the radial direction compared with the tangential one) is mildly radial, with 0.2 <β< 0.4. For stars with [Fe/H] > −1.7, however, we measure extreme values of β∼ 0.9. Across the metallicity range considered, namely−3 < [Fe/H] < −1, the stellar halo’s spin is minimal, at the level of |$20\lt \bar{v}_{\theta }(\mathrm{kms}^{-1}) \lt 30$|⁠. Using a suite of cosmological zoom-in simulations of halo formation, we deduce that the observed acute anisotropy is inconsistent with the continuous accretion of dwarf satellites. Instead, we argue, the stellar debris in the inner halo was deposited in a major accretion event by a satellite with Mvir > 1010M⊙ around the epoch of the Galactic disc formation, between 8 and 11 Gyr ago. The radical halo anisotropy is…

We present Bayesian Analysis of Galaxies for Physical Inference and Parameter EStimation, or bagpipes, a new python tool that can be used to rapidly generate complex model galaxy spectra and to fit these to arbitrary combinations of spectroscopic and photometric data using the multinest nested sampling algorithm. We extensively test our ability to recover realistic star formation histories (SFHs) by fitting mock observations of quiescent galaxies from the mufasa simulation. We then perform a detailed analysis of the SFHs of a sample of 9289 quiescent galaxies from UltraVISTA with stellar masses, M* > 1010 M⊙ and redshifts 0.25 < |$z$| < 3.75. The majority of our sample exhibit SFHs that rise gradually then quench relatively rapidly over 1−2 Gyr. This behaviour is consistent with recent cosmological hydrodynamic simulations, where AGN-driven feedback in the low-accretion (jet) mode is the dominant quenching mechanism. At |$z$| > 1, we also find a class of objects with SFHs that rise and fall very rapidly, with quenching time-scales of <1 Gyr, consistent with quasar-mode AGN feedback.…

A new line list for H 16 2 O is presented.This line list, which is called POKAZATEL, includes transitions between rotational-vibrational energy levels up to 41 000 cm -1 and is the most complete to date.The potential energy surface (PES) used for producing the line list was obtained by fitting a high-quality ab initio PES to experimental energy levels with energies of 41 000 cm -1 and for rotational excitations up to J = 5.The final line list comprises all energy levels up to 41 000 cm -1 and rotational angular momentum J up to 72.An accurate ab initio dipole moment surface was used for the calculation of line intensities and reproduces high-precision experimental intensity data with an accuracy close to 1 per cent.The final line list uses empirical energy levels, whenever they are available, to ensure that line positions are reproduced as accurately as possible.The POKAZATEL line list contains over 5 billion transitions and is available from the ExoMol website (www.exomol.com)and the CDS data base.

Determining the properties of old stellar populations (those with age >1 Gyr) has long involved the comparison of their integrated light, either in the form of photometry or spectroscopic indexes, with empirical or synthetic templates. Here we re-evaluate the properties of old stellar populations using a new set of stellar population synthesis models, designed to incorporate the effects of binary stellar evolution pathways as a function of stellar mass and age. We find that single-aged stellar population models incorporating binary stars, as well as new stellar evolution and atmosphere models, can reproduce the colours and spectral indices observed in both globular clusters and quiescent galaxies. The best-fitting model populations are often younger than those derived from older spectral synthesis models and may also lie at slightly higher metallicities.

agama is a publicly available software library for a broad range of applications in the field of stellar dynamics. It provides methods for computing the gravitational potential of arbitrary analytic density profiles or N-body models, orbit integration and analysis, transformations between position/velocity and action/angle variables, distribution functions expressed in terms of actions and their moments, and iterative construction of self-consistent multicomponent galaxy models. Applications include the inference about the structure of Milky Way or other galaxies from observations of stellar kinematics, preparation of equilibrium initial conditions for N-body simulations, and analysis of snapshots from simulations. The library is written in C++ , provides a python interface, and can be coupled to other stellar-dynamical software: amuse, galpy, and nemo. It is hosted at http://github.com/GalacticDynamics-Oxford/Agama.

We have determined masses, stellar mass functions and structural parameters of 112 Milky Way globular clusters by fitting a large set of N-body simulations to their velocity dispersion and surface density profiles. The velocity dispersion profiles were calculated based on a combination of more than 15,000 high-precision radial velocities which we derived from archival ESO/VLT and Keck spectra together with ~20,000 published radial velocities from the literature. Our fits also include the stellar mass functions of the globular clusters, which are available for 47 clusters in our sample, allowing us to self-consistently take the effects of mass segregation and ongoing cluster dissolution into account. We confirm the strong correlation between the global mass functions of globular clusters and their relaxation times recently found by Sollima & Baumgardt (2017). We also find a correlation of the escape velocity from the centre of a globular cluster and the fraction of first generation stars (FG) in the cluster recently derived for 57 globular clusters by Milone et al. (2017), but no…

Various theoretical models treating the effect of stellar irradiation on planetary envelopes predict the presence of a radius valley, i.e. a bimodal distribution of planet radii, with super-Earths and sub-Neptune planets separated by a valley at around |${\approx } 2\, \text{R}_\oplus$|⁠. Such a valley has been observed recently, owing to an improvement in the precision of stellar and therefore planetary radii. Here, we investigate the presence, location, and shape of such a valley using a small sample with highly accurate stellar parameters determined from asteroseismology, which includes 117 planets with a median uncertainty on the radius of 3.3 per cent. We detect a clear bimodal distribution, with super-Earths (⁠|${\approx } 1.5\, \text{R}_\oplus$|⁠) and sub-Neptunes (≈2.5 R⊕) separated by a deficiency around |$2\, \text{R}_\oplus$|⁠. We furthermore characterize the slope of the valley as a power law R∝Pγ with |$\gamma = {-0.09^{+0.02}_{-0.04}}$|⁠. A negative slope is consistent with models of photoevaporation, but not with the late formation of rocky planets in a gas-poor…

Recent observations identify a valley in the radius distribution of small exoplanets, with planets in the range 1.5–2.0 R⊕ significantly less common than somewhat smaller or larger planets. This valley may suggest a bimodal population of rocky planets that are either engulfed by massive gas envelopes that significantly enlarge their radius, or do not have detectable atmospheres at all. One explanation of such a bimodal distribution is atmospheric erosion by high-energy stellar photons. We investigate an alternative mechanism: the luminosity of the cooling rocky core, which can completely erode light envelopes while preserving heavy ones, produces a deficit of intermediate sized planets. We evolve planetary populations that are derived from observations using a simple analytical prescription, accounting self-consistently for envelope accretion, cooling and mass-loss, and demonstrate that core-powered mass-loss naturally reproduces the observed radius distribution, regardless of the high-energy incident flux. Observations of planets around different stellar types may distinguish…

We present a new 3D map of interstellar dust reddening, covering three quarters of the sky (declinations of δ ≳ −30°) out to a distance of several kiloparsecs. The map is based on high-quality stellar photometry of 800 million stars from Pan-STARRS 1 and 2MASS. We divide the sky into sightlines containing a few hundred stars each, and then infer stellar distances and types, along with the line-of-sight dust distribution. Our new map incorporates a more accurate average extinction law and an additional 1.5 yr of Pan-STARRS 1 data, tracing dust to greater extinctions and at higher angular resolutions than our previous map. Out of the plane of the Galaxy, our map agrees well with 2D reddening maps derived from far-infrared dust emission. After accounting for a 25 per cent difference in scale, we find a mean scatter of ∼10 per cent between our map and the Planck far-infrared emission-based dust map, out to a depth of 0.8 mag in E(gP1 − rP1), with the level of agreement varying over the sky. Our map can be downloaded at http://argonaut.skymaps.info, or from the Harvard Dataverse (Green…

We study the population of supermassive black holes (SMBHs) and their effects on massive central galaxies in the IllustrisTNG cosmological hydrodynamical simulations of galaxy formation. The employed model for SMBH growth and feedback assumes a two-mode scenario in which the feedback from active galactic nuclei occurs through a kinetic, comparatively efficient mode at low accretion rates relative to the Eddington limit, and in the form of a thermal, less efficient mode at high accretion rates. We show that the quenching of massive central galaxies happens coincidently with kinetic-mode feedback, consistent with the notion that active supermassive black holes cause the low specific star formation rates observed in massive galaxies. However, major galaxy mergers are not responsible for initiating most of the quenching events in our model. Up to black hole masses of about |$10^{8.5}\, {\rm M}_{\odot}$|⁠, the dominant growth channel for SMBHs is in the thermal mode. Higher mass black holes stay mainly in the kinetic mode and gas accretion is self-regulated via their feedback, which…

We have generated synthetic images of ∼27 000 galaxies from the IllustrisTNG and the original Illustris hydrodynamic cosmological simulations, designed to match Pan-STARRS observations of log 10 (M * /M ) ≈ 9.8-11.3galaxies at z ≈ 0.05.Most of our synthetic images were created with the SKIRT radiative transfer code, including the effects of dust attenuation and scattering, and performing the radiative transfer directly on the Voronoi mesh used by the simulations themselves.We have analysed both our synthetic and real Pan-STARRS images with the newly developed statmorph code, which calculates non-parametric morphological diagnostics -including the Gini-M 20 and concentration-asymmetry-smoothness statisticsand performs 2D Sérsic fits.Overall, we find that the optical morphologies of IllustrisTNG galaxies are in good agreement with observations, and represent a substantial improvement compared to the original Illustris simulation.In particular, the locus of the Gini-M 20 diagram is consistent with that inferred from observations, while the median trends with stellar mass of all the…

We have derived the mean proper motions and space velocities of 154 Galactic globular clusters and the velocity dispersion profiles of 141 globular clusters based on a combination of Gaia DR2 proper motions with ground-based line-of-sight velocities. Combining the velocity dispersion profiles derived here with new measurements of the internal mass functions allows us to model the internal kinematics of 144 clusters, more than 90% of the currently known Galactic globular cluster population. We also derive the initial cluster masses by calculating the cluster orbits backwards in time applying suitable recipes to account for mass loss and dynamical friction. We find a correlation between the stellar mass function of a globular cluster and the amount of mass lost from the cluster, pointing to dynamical evolution as one of the mechanisms shaping the mass function of stars in clusters. The mass functions also show strong evidence that globular clusters started with a bottom-light initial mass function. Our simulations show that the currently surviving globular cluster population has lost…

The vertical structure and dynamics of stars in our local Galactic neighbourhood contains much information about the local distribution of visible and dark matter and of perturbations to the Milky Way disc. We use data on the positions and velocities of stars in the solar neighbourhood from Gaia Data Release 2 (DR2) and large spectroscopic surveys to investigate the vertical number counts and mean velocity trend as a function of distance from the local Galactic mid-plane. We perform a detailed measurement of the wave-like north–south asymmetry in the vertical number counts, which reveals a number of deficits at heights ≈0.4, ≈0.9, and |${\approx } 1.5\, \mathrm{kpc}$|⁠, and peaks at ≈0.2, ≈0.7, and |${\approx } 1.1\, \mathrm{kpc}$|⁠. We find that the asymmetry pattern is independent of colour. The mean vertical velocity is almost constant to |${\lt }1\, \mathrm{km\, s}^{-1}$| within a few 100 pc from the mid-plane and then displays a north–south symmetric dip at |${\approx }0.5\, \mathrm{kpc}$| with an amplitude of |${\approx } 2\, \mathrm{km\, s}^{-1}$| that is a plausible velocity…

The All-Sky Automated Survey for Supernovae (ASAS-SN) is the first optical survey to routinely monitor the whole sky with a cadence of ∼2–3 d down to V ≲ 17 mag. ASAS-SN has monitored the whole sky since 2014, collecting ∼100–500 epochs of observations per field. The V-band light curves for candidate variables identified during the search for supernovae are classified using a random forest classifier and visually verified. We present a catalogue of 66 179 bright, new variable stars discovered during our search for supernovae, including 27 479 periodic variables and 38 700 irregular variables. V-band light curves for the ASAS-SN variables are available through the ASAS-SN variable stars data base (https://asas-sn.osu.edu/variables). The data base will begin to include the light curves of known variable stars in the near future along with the results for a systematic, all-sky variability survey.

We present emerge, an Empirical ModEl for the foRmation of GalaxiEs, describing the evolution of individual galaxies in large volumes from z ∼ 10 to the present day. We assign a star formation rate to each dark matter halo based on its growth rate, which specifies how much baryonic material becomes available, and the instantaneous baryon conversion efficiency, which determines how efficiently this material is converted to stars, thereby capturing the baryonic physics. Satellites are quenched following the delayed-then-rapid model, and they are tidally disrupted once their subhalo has lost a significant fraction of its mass. The model is constrained with observed data extending out to high redshift. The empirical relations are very flexible, and the model complexity is increased only if required by the data, assessed by several model selection statistics. We find that for the same final halo mass galaxies can have very different star formation histories. Galaxies that are quenched at z = 0 typically have a higher peak star formation rate compared to their star-forming counterparts.…

We present a catalogue of white dwarf candidates selected from the second data release of Gaia (DR2). We used a sample of spectroscopically confirmed white dwarfs from the Sloan Digital Sky Survey (SDSS) to map the entire space spanned by these objects in the Gaia Hertzsprung–Russell diagram. We then defined a set of cuts in absolute magnitude, colour, and a number of Gaia quality flags to remove the majority of contaminating objects. Finally, we adopt a method analogous to the one presented in our earlier SDSS photometric catalogues to calculate a probability of being a white dwarf (PWD) for all Gaia sources that passed the initial selection. The final catalogue is composed of |$486\, 641$| stars with calculated PWD from which it is possible to select a sample of |${\simeq } 260\, 000$| high-confidence white dwarf candidates in the magnitude range 8 < G < 21. By comparing this catalogue with a sample of SDSS white dwarf candidates, we estimate an upper limit in completeness of 85 per cent for white dwarfs with G ≤ 20 mag and Teff >7000 K, at high Galactic latitudes (|b| > 20°).…

We present the extended GALEX Arecibo SDSS Survey (xGASS), a gas fraction-limited censusof the atomic hydrogen (H I) gas content of 1179 galaxies selected only by stellar mass (M* = 109-1011.5 Mo˙) and redshift (0.01

Abstract We present a morphological catalogue for ∼670 000 galaxies in the Sloan Digital Sky Survey in two flavours: T-type, related to the Hubble sequence, and Galaxy Zoo 2 (GZ2 hereafter) classification scheme. By combining accurate existing visual classification catalogues with machine learning, we provide the largest and most accurate morphological catalogue up to date. The classifications are obtained with Deep Learning algorithms using Convolutional Neural Networks (CNNs). We use two visual classification catalogues, GZ2 and Nair & Abraham (2010), for training CNNs with colour images in order to obtain T-types and a series of GZ2 type questions (disc/features, edge-on galaxies, bar signature, bulge prominence, roundness, and mergers). We also provide an additional probability enabling a separation between pure elliptical (E) from S0, where the T-type model is not so efficient. For the T-type, our results show smaller offset and scatter than previous models trained with support vector machines. For the GZ2 type questions, our models have large accuracy (>97 per cent), precision…

The first gravitational wave detections of mergers between black holes and neutron stars represent a remarkable new regime of high-energy transient astrophysics.The signals observed with LIGO-Virgo detectors come from mergers of extreme physical objects which are the end products of stellar evolution in close binary systems.To better understand their origin and merger rates, we have performed binary population syntheses at different metallicities using the new grid-based binary population synthesis code ComBinE.Starting from newborn pairs of stars, we follow their evolution including mass loss, mass transfer and accretion, common envelopes and supernova explosions.We apply the binding energies of common envelopes based on dense grids of detailed stellar structure models, make use of improved investigations of the subsequent Case BB Roche-lobe overflow and scale supernova kicks according to the stripping of the exploding stars.We demonstrate that all the double black hole mergers, GW150914, LVT151012, GW151226, GW170104, GW170608 and GW170814, as well as the double neutron star…

We use the age-metallicity distribution of 96 Galactic globular clusters (GCs) to infer the formation and assembly history of the Milky Way (MW), culminating in the reconstruction of its merger tree. Based on a quantitative comparison of the Galactic GC population to the 25 cosmological zoom-in simulations of MW-mass galaxies in the E-MOSAICS project, which self-consistently model the formation and evolution of GC populations in a cosmological context, we find that the MW assembled quickly for its mass, reaching $\{25,50\}\%$ of its present-day halo mass already at $z=\{3,1.5\}$ and half of its present-day stellar mass at $z=1.2$. We reconstruct the MW's merger tree from its GC age-metallicity distribution, inferring the number of mergers as a function of mass ratio and redshift. These statistics place the MW's assembly $\textit{rate}$ among the 72th-94th percentile of the E-MOSAICS galaxies, whereas its $\textit{integrated}$ properties (e.g. number of mergers, halo concentration) match the median of the simulations. We conclude that the MW has experienced no major mergers (mass…

The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of the Milky Way and designed to deliver chemical information complementary to a large number of stars covered by the Gaia mission.We present the GALAH second public data release (GALAH DR2) containing 342,682 stars.For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community.Here we present the target selection, observation, data reduction and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances.For the stellar analysis, we have used a multi-step approach.We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels (T eff , log g, [Fe/H], [X/Fe], v mic , v sin i, A K S ) for a representative training set of stars.This information is then propagated to the whole survey with the data-driven method of The Cannon.Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input…

Six gravitational wave events have been reported by the LIGO-Virgo collaboration (LVC), five of them associated with black hole binary (BHB) mergers and one with a double neutron star (DNS) merger, while the coalescence of a black hole–neutron star (BHNS) binary is still missing. We investigate the progenitors of double compact object binaries with our population-synthesis code mobse. mobse includes advanced prescriptions for mass loss by stellar winds (depending on metallicity and on the Eddington ratio) and a formalism for core-collapse, electron-capture and (pulsational) pair instability supernovae. We investigate the impact of progenitor’s metallicity, of the common-envelope parameter α and of the natal kicks on the properties of DNSs, BHNSs and BHBs. We find that neutron-star (NS) masses in DNSs span from 1.1 to 2.0 M⊙, with a preference for light NSs, while NSs in merging BHNSs have mostly large masses (1.3−2.0M⊙). BHs in merging BHNSs are preferentially of low mass (5−15M⊙). BH masses in merging BHBs strongly depend on the progenitor’s metallicity and span from ∼5 to ∼45 M⊙.…

We present a comprehensive study of the abundance evolution of the elements from H to U in the Milky Way halo and local disk. We use a consistent chemical evolution model, metallicity dependent isotopic yields from low and intermediate mass stars and yields from massive stars which include, for the first time, the combined effect of metallicity, mass loss and rotation for a large grid of stellar masses and for all stages of stellar evolution. The yields of massive stars are weighted by a metallicity dependent function of the rotational velocities, constrained by observations as to obtain a primary-like $^{14}$N behavior at low metallicity and to avoid overproduction of s-elements at intermediate metallicities. We show that the solar system isotopic composition can be reproduced to better than a factor of two for isotopes up to the Fe-peak, and at the 10\% level for most pure s-isotopes, both light ones (resulting from the weak s-process in rotating massive stars) and the heavy ones (resulting from the main s-process in low and intermediate mass stars). We conclude that the light…

Abstract We present results from the first population synthesis study of protostellar discs. We analyse the evolution and properties of a large sample of protostellar discs formed in a radiation hydrodynamical simulation of star cluster formation. Due to the chaotic nature of the star formation process, we find an enormous diversity of young protostellar discs, including misaligned discs, and discs whose orientations vary with time. Star–disc interactions truncate discs and produce multiple systems. Discs may be destroyed in dynamical encounters and/or through ram-pressure stripping, but reform by later gas accretion. We quantify the distributions of disc mass and radii for protostellar ages up to ≈105 yr. For low-mass protostars, disc masses tend to increase with both age and protostellar mass. Disc radii range from of order 10 to a few hundred au, grow in size on time-scales ≲ 104 yr, and are smaller around lower mass protostars. The radial surface density profiles of isolated protostellar discs are flatter than the minimum mass solar nebula model, typically scaling as Σ ∝ r−1.…

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of five star-forming galaxies at redshifts z in the range 0.2993-0.4317 and with high emission-line flux ratios O32=[OIII]5007/[OII]3727 ~ 8-27 aiming to detect the Lyman continuum (LyC) emission. We detect LyC emission in all galaxies with the escape fractions fesc(LyC) in a range of 2-72 per cent. A narrow Ly-alpha emission line with two peaks in four galaxies and with three peaks in one object is seen in medium-resolution COS spectra with a velocity separation between the peaks Vsep varying from ~153 km/s to ~345 km/s. We find a general increase of the LyC escape fraction with increasing O32 and decreasing stellar mass M*, but with a large scatter of fesc(LyC). A tight anti-correlation is found between fesc(LyC) and Vsep making Vsep a good parameter for the indirect determination of the LyC escape fraction. We argue that one possible source driving the escape of ionizing radiation is stellar winds and radiation from hot massive stars.

We introduce a new model for the structure and evolution of the gas in galactic discs. In the model the gas is in vertical pressure and energy balance. Star formation feedback injects energy and momentum, and non-axisymmetric torques prevent the gas from becoming more than marginally gravitationally unstable. From these assumptions we derive the relationship between galaxies' bulk properties (gas surface density, stellar content, and rotation curve) and their star formation rates, gas velocity dispersions, and rates of radial inflow. We show that the turbulence in discs can be powered primarily by star formation feedback, radial transport, or a combination of the two. In contrast to models that omit either radial transport or star formation feedback, the predictions of this model yield excellent agreement with a wide range of observations, including the star formation law measured in both spatially resolved and unresolved data, the correlation between galaxies' star formation rates and velocity dispersions, and observed rates of radial inflow. The agreement holds across a wide range…

Double neutron stars (DNSs) have been observed as Galactic radio pulsars, and the recent discovery of gravitational waves from the DNS merger GW170817 adds to the known DNS population. We perform rapid population synthesis of massive binary stars and discuss model predictions, including DNS formation rates, mass distributions, and delay time distributions. We vary assumptions and parameters of physical processes such as mass transfer stability criteria, supernova natal kick distributions, remnant mass prescriptions, and common-envelope energetics. We compute the likelihood of observing the orbital period–eccentricity distribution of the Galactic DNS population under each of our population synthesis models, allowing us to quantitatively compare the models. We find that mass transfer from a stripped post-helium-burning secondary (case BB) on to a neutron star is most likely dynamically stable. We also find that a natal kick distribution composed of both low (Maxwellian |$\sigma =30\, \rm km\, s^{-1}$|⁠) and high (⁠|$\sigma =265\, \rm km\, s^{-1}$|⁠) components is preferred over a…

To gain understanding of the complicated, non-linear, and numerical processes associated with the tidal evolution of dark matter subhaloes in numerical simulation, we perform a large suite of idealized simulations that follow individual N-body subhaloes in a fixed, analytical host halo potential. By varying both physical and numerical parameters, we investigate under what conditions the subhaloes undergo disruption. We confirm the conclusions from our more analytical assessment in van den Bosch et al. that most disruption is numerical in origin; as long as a subhalo is resolved with sufficient mass and force resolution, a bound remnant survives. This implies that state-of-the-art cosmological simulations still suffer from significant overmerging. We demonstrate that this is mainly due to inadequate force softening, which causes excessive mass loss and artificial tidal disruption. In addition, we show that subhaloes in N-body simulations are susceptible to a runaway instability triggered by the amplification of discreteness noise in the presence of a tidal field. These two processes…

The coronal activity–rotation relationship is considered to be a proxy for the underlying stellar dynamo responsible for magnetic activity in solar and late-type stars. While this has been studied in considerable detail for partly convective stars that are believed to operate an interface dynamo, it is poorly unconstrained in fully convective stars that lack the necessary shear layer between radiative core and the convective envelope. We present new X-ray observations of 19 slowly rotating fully convective stars with rotation periods from the MEarth Project. We use these to calculate X-ray luminosities (or upper limits for undetected sources) and combine these with existing measurements. We confirm the existence of fully convective stars in the X-ray unsaturated regime and find that these objects follow the same rotation–activity relationship seen for partly convective stars. We measure the power-law slope of the relationship between Rossby number (the ratio of the rotation period to the convective turnover time) and the fractional X-ray luminosity for X-ray unsaturated fully…

We compare shadows cast by Schwarzschild black holes with those produced by two classes of naked singularities that result from gravitational collapse of spherically symmetric matter. The latter models consist of an interior naked singularity space–time restricted to radii r ≤ Rb, matched to Schwarzschild space–time outside the boundary radius Rb. While a black hole always has a photon sphere and always casts a shadow, we find that the naked singularity models have photon spheres only if a certain parameter M0 that characterizes these models satisfies M0 ≥ 2/3, or equivalently, if Rb ≤ 3M, where M is the total mass of the object. Such models do produce shadows. However, models with M0 < 2/3 (or Rb > 3M) have no photon sphere and do not produce a shadow. Instead, they produce an interesting ‘full-moon’ image. These results imply that the presence of a shadow does not by itself prove that a compact object is necessarily a black hole. The object could be a naked singularity with M0 ≥ 2/3, and we will need other observational clues to distinguish the two possibilities. On the other…

Primordial black holes (PBHs) could provide the dark matter in various mass windows below 102 M⊙ and those of 30 M⊙ might explain the LIGO events. PBHs much larger than this might have important consequences even if they provide only a small fraction of the dark matter. In particular, they could generate cosmological structure either individually through the ‘seed’ effect or collectively through the ‘Poisson’ effect, thereby alleviating some problems associated with the standard cold dark matter scenario. If the PBHs all have a similar mass and make a small contribution to the dark matter, then the seed effect dominates on small scales, in which case PBHs could generate the supermassive black holes in galactic nuclei or even galaxies themselves. If they have a similar mass and provide the dark matter, the Poisson effect dominates on all scales and the first bound clouds would form earlier than in the usual scenario, with interesting observational consequences. If the PBHs have an extended mass spectrum, which is more likely, they could fulfill all three roles – providing the dark…

We investigate the long-term evolution of black hole accretion discs formed in neutron star mergers. These discs expel matter that contributes to an r-process kilonova, and can produce relativistic jets powering short gamma-ray bursts. Here we report the results of a three-dimensional, general-relativistic magnetohydrodynamic (GRMHD) simulation of such a disc which is evolved for long enough (∼9 s, or ∼6 × 105rg/c) to achieve completion of mass ejection far from the disc. Our model starts with a poloidal field, and fully resolves the most unstable mode of the magnetorotational instability. We parametrize the dominant microphysics and neutrino cooling effects, and compare with axisymmetric hydrodynamic models with shear viscosity. The GRMHD model ejects mass in two ways: a prompt MHD-mediated outflow and a late-time, thermally driven wind once the disc becomes advective. The total amount of unbound mass ejected (⁠|$0.013\, \mathrm{M}_\odot$|⁠, or |${\simeq } 40{{\ \rm per\ cent}}$| of the initial torus mass) is twice as much as in hydrodynamic models, with higher average velocity…

We present the SPHINX suite of cosmological adaptive mesh refinement simulations, the first radiation-hydrodynamical simulations to simultaneously capture large-scale reionization and the escape of ionizing radiation from thousands of resolved galaxies.Our 5 and 10 co-moving Mpc volumes resolve haloes down to the atomic cooling limit and model the interstellar medium with better than ≈10 pc resolution.The project has numerous goals in improving our understanding of reionization and making predictions for future observations.In this first paper, we study how the inclusion of binary stars in computing stellar luminosities impacts reionization, compared to a model that includes only single stars.Owing to the suppression of galaxy growth via strong feedback, our galaxies are in good agreement with observational estimates of the galaxy luminosity function.We find that binaries have a significant impact on the timing of reionization: with binaries, our boxes are 99.9 percent ionized by volume at z ≈ 7, while without them our volumes fail to reionize by z = 6.These results are robust to…

We combine Dark Energy Survey Year 1 clustering and weak lensing data with baryon acoustic oscillations and Big Bang nucleosynthesis experiments to constrain the Hubble constant. Assuming a flat ΛCDM model with minimal neutrino mass (∑mν = 0.06 eV), we find |$H_0=67.4^{+1.1}_{-1.2}\ \rm {km\,\rm s^{-1}\,\rm Mpc^{-1}}$| (68 per cent CL). This result is completely independent of Hubble constant measurements based on the distance ladder, cosmic microwave background anisotropies (both temperature and polarization), and strong lensing constraints. There are now five data sets that: (a) have no shared observational systematics; and (b) each constrains the Hubble constant with fractional uncertainty at the few-per cent level. We compare these five independent estimates, and find that, as a set, the differences between them are significant at the 2.5σ level (χ2/dof = 24/11, probability to exceed = 1.1 per cent). Having set the threshold for consistency at 3σ, we combine all five data sets to arrive at |$H_0=69.3^{+0.4}_{-0.6}\ \rm {km\,\mathrm{ s}^{-1}\,\mathrm{ Mpc}^{-1}}$|⁠.

Absolute parameters of 509 main-sequence stars selected from the components of detached-eclipsing spectroscopic binaries in the Solar neighbourhood are used to study mass-luminosity, mass-radius and mass-effective temperature relations (MLR, MRR and MTR). The MLR function is found better if expressed by a six-piece classical MLR ($L \propto M^α$) rather than a fifth or a sixth degree polynomial within the mass range of $0.179\leq M/M_{\odot}\leq 31$. The break points separating the mass-ranges with classical MLR do not appear to us to be arbitrary. Instead, the data indicate abrupt changes along the mass axis in the mean energy generation per unit of stellar mass. Unlike the MLR function, the MRR and MTR functions cannot be determined over the full range of masses. A single piece MRR function is calibrated from the radii of stars with $M\leq1.5M_{\odot}$, while a second single piece MTR function is found for stars with $M>1.5M_{\odot}$. The missing part of the MRR is computed from the MLR and MTR, while the missing part of the MTR is computed from the MLR and MRR. As a result, we…

We study the interactions of a relativistic jet with a dense turbulent gaseous disc of radius ∼2 kpc. We have performed a suite of simulations with different mean density, jet power, and orientation. Our results show that: (A) The relativistic jet couples strongly with the gas in the inner kpc, creating a cavity and launching outflows. (B) The high pressure bubble inflated by the jet and its back-flow compresses the disc at the outer edges, driving inflows within the disc. (C) Jets inclined towards the disc affect the disc more and launch sub-relativistic, wide-angled outflows along the minor axis. (D) Shocks driven directly by the jet and the jet-driven energy bubble raise the velocity dispersion throughout the disc by several times its initial value. (E) Compression by the jet-driven shocks can enhance the star formation rate in the disc, especially in a ring-like geometry close to the axis. However, enhanced turbulent dispersion in the disc also leads to quenching of star formation. Whether positive or negative feedback dominates depends on jet power, ISM density, jet orientation…

We develop a new spectral model for the broad-band spectral energy distribution (SED) of active galactic nuclei (AGN). This includes an outer standard disc, an inner warm Comptonizing region to produce the soft X-ray excess and a hot corona. We tie these together energetically by assuming Novikov–Thorne emissivity, and use this to define a size scale for the hard X-ray corona as equal to the radius where the remaining accretion energy down to the black hole can power the observed X-ray emission. We test this on three AGN with well-defined SEDs as well as on larger samples to show that the average hard X-ray luminosity is always approximately a few per cent of the Eddington luminosity across a large range of Eddington ratio. As a consequence, the radial size scale required for gravity to power the X-ray corona has to decrease with increasing Eddington fraction. For the first time, we hardwire this into the spectral models, and set the hard X-ray spectral index self-consistently from the ratio of the hard X-ray luminosity to intercepted seed photon luminosity from the disc. This…

We present a new, open source, free semi-analytic model (SAM) of galaxy formation, Shark, designed to be highly flexible and modular, allowing easy exploration of different physical processes and ways of modelling them. We introduce the philosophy behind Shark and provide an overview of the physical processes included in the model. Shark is written in C++11 and has been parallelized with OpenMP. In the released version (v1.1), we implement several different models for gas cooling, active galactic nuclei, stellar and photo-ionisation feedback, and star formation (SF). We demonstrate the basic performance of Shark using the Planck15 cosmology SURFS simulations, by comparing against a large set of observations, including: the stellar mass function (SMF) and stellar-halo mass relation at z=0-4; the cosmic evolution of the star formation rate density (SFRD), stellar mass, atomic and molecular hydrogen; local gas scaling relations; and structural galaxy properties, finding excellent agreement. Significant improvements over previous SAMs are seen in the mass-size relation for disks/bulges,…

We model the broad-band (optical/UV and X-ray) continuum spectrum of the ‘changing-look’ active galactic nucleus (AGN) Mrk 1018, as it fades from Seyfert 1 to 1.9 in ∼ 8 years. The brightest spectrum, with Eddington ratio L/LEdd ∼ 0.08 has a typical type 1 AGN continuum, with a strong ‘soft X-ray excess’ spanning between the UV and soft X-rays. The dimmest spectrum, at L/LEdd ∼ 0.006, is very different in shape as well as luminosity, with the soft excess dropping by much more than the hard X-rays. The soft X-ray excess produces most of the ionizing photons, so its dramatic drop leads to the disappearance of the broad-line region, driving the ‘changing-look’ phenomena. This spectral hardening appears similar to the soft-to-hard state transition in black hole binaries at L/LEdd ∼ 0.02, where the inner disc evaporates into an advection dominated accretion flow, while the overall drop in luminosity appears consistent with the hydrogen ionization disc instability. None the less, both processes happen much faster in Mrk 1018 than predicted by disc theory. We critically examine scaling…

We infer the mass distribution of neutron stars in binary systems using a flexible Gaussian mixture model and use Bayesian model selection to explore evidence for multi-modality and a sharp cut-off in the mass distribution. We find overwhelming evidence for a bimodal distribution, in agreement with previous literature, and report for the first time positive evidence for a sharp cut-off at a maximum neutron star mass. We measure the maximum mass to be $2.0M_\odot < m_\mathrm{max} < 2.2M_\odot$ (68\%), $2.0M_\odot < m_\mathrm{max}< 2.6M_\odot$ (90\%), and evidence for a cut-off is robust against the choice of model for the mass distribution and to removing the most extreme (highest mass) neutron stars from the dataset. If this sharp cut-off is interpreted as the maximum stable neutron star mass allowed by the equation of state of dense matter, our measurement puts constraints on the equation of state. For a set of realistic equations of state that support $>2M_\odot$ neutron stars, our inference of $m_\mathrm{max}$ is able to distinguish between models at odds ratios of up to $12:1$,…

We study molecular outflows in a sample of 45 local galaxies, both star forming and AGN, primarily by using CO data from the ALMA archive and from the literature.For a subsample we also compare the molecular outflow with the ionized and neutral atomic phases.We infer an empirical analytical function relating the outflow rate simultaneously to the SFR, L AGN , and galaxy stellar mass; this relation is much tighter than the relations with the individual quantities.The outflow kinetic power shows a larger scatter than in previous studies, spanning from 0.1 to 5 per cent of L AGN , while the momentum rate ranges from 1 to 30 times L AGN /c, indicating that these outflows can be both energy-driven, but with a broad range of coupling efficiencies with the ISM, and radiation pressure-driven.For about 10 per cent of the objects the outflow properties significantly exceed the maximum theoretical values; we interpret these as "fossil outflows" resulting from activity of a past strong AGN, which has now faded.We estimate that, in the stellar mass range probed here (> 10 10 M ), less than 5 per…

The mass–period or radius–period distribution of close-in exoplanets shows a paucity of intermediate mass/size (sub-Jovian) planets with periods ≲3 d. We show that this sub-Jovian desert can be explained by the photoevaporation of highly irradiated sub-Neptunes and the tidal disruption barrier for gas giants undergoing high-eccentricity migration. The distinctive triangular shape of the sub-Jovain desert results from the fact that photoevaporation is more effective closer to the host star, and that in order for a gas giant to tidally circularize closer to the star without tidal disruption it needs to be more massive. Our work indicates that super-Earths/mini-Neptunes and hot-Jupiters had distinctly separate formation channels and arrived at their present locations at different times.

We present cosmological parameter constraints from a joint analysis of three cosmological probes: the tomographic cosmic shear signal in ∼450 deg2 of data from the Kilo Degree Survey (KiDS), the galaxy-matter cross-correlation signal of galaxies from the Galaxies And Mass Assembly (GAMA) survey determined with KiDS weak lensing, and the angular correlation function of the same GAMA galaxies. We use fast power spectrum estimators that are based on simple integrals over the real-space correlation functions, and show that they are practically unbiased over relevant angular frequency ranges. We test our full pipeline on numerical simulations that are tailored to KiDS and retrieve the input cosmology. By fitting different combinations of power spectra, we demonstrate that the three probes are internally consistent. For all probes combined, we obtain |$S_8\equiv \sigma _8 \sqrt{\Omega _{\rm m}/0.3}=0.800_{-0.027}^{+0.029}$|⁠, consistent with Planck and the fiducial KiDS-450 cosmic shear correlation function results. Marginalizing over wide priors on the mean of the tomographic redshift…

Gravitational potential fluctuations driven by bursty star formation can kinematically ‘heat up’ dark matter at the centres of dwarf galaxies. A key prediction of such models is that, at a fixed dark matter halo mass, dwarfs with a higher stellar mass will have a lower central dark matter density. We use stellar kinematics and HI gas rotation curves to infer the inner dark matter densities of eight dwarf spheroidal and eight dwarf irregular galaxies with a wide range of star formation histories. For all galaxies, we estimate the dark matter density at a common radius of 150 pc, |$\rho _{\rm DM}(150\, \mathrm{pc})$|⁠. We find that our sample of dwarfs falls into two distinct classes. Those that stopped forming stars over 6 Gyr ago favour central densities |$\rho _{\rm DM}(150\, \mathrm{pc})\gt 10^8$| M⊙ kpc−3, consistent with cold dark matter cusps, while those with more extended star formation favour |$\rho _{\rm DM}(150\, \mathrm{pc})\lt 10^8$| M⊙ kpc−3, consistent with shallower dark matter cores. Using abundance matching to infer pre-infall halo masses, M200, we show that this…

We constrain the mass-richness scaling relation of redMaPPer galaxy clusters identified in the Dark Energy Survey Year 1 data using weak gravitational lensing.We split clusters into 4 × 3 bins of richness λ and redshift z for λ ≥ 20 and 0.2 ≤ z ≤ 0.65 and measure the mean masses of these bins using their stacked weak lensing signal.By modelling the scaling relation as M 200m |λ, z = M 0 (λ/40) F ((1 + z)/1.35)G , we constrain the normalization of the scaling relation at the 5.0 per cent level, finding M 0 = [3.081± 0.075(stat) ± 0.133(sys)] • 10 14 M at λ = 40 and z = 0.35.The recovered richness scaling index is F = 1.356 ± 0.051 (stat) ± 0.008 (sys) and the redshift scaling index G = -0.30± 0.30 (stat) ± 0.06 (sys).These are the tightest measurements of the normalization and richness scaling index made to date from a weak lensing experiment.We use a semi-analytic covariance matrix to characterize the statistical errors in the recovered weak lensing profiles.Our analysis accounts for the following sources of systematic error: shear and photometric redshift errors, cluster…

We analyze observations of eight quiescent low-mass X-ray binaries in globular clusters and combine them to determine the neutron star mass-radius curve and the equation of state of dense matter. We determine the effect that several uncertainties may have on our results, including uncertainties in the distance, the atmosphere composition, the neutron star maximum mass, the neutron star mass distribution, the possible presence of a hotspot on the neutron star surface, and the prior choice for the equation of state of dense matter. We find that the radius of a 1.4 solar mass neutron star is most likely from 10 to 14 km and that tighter constraints are only possible with stronger assumptions about the nature of the neutron stars, the systematics of the observations, or the nature of dense matter. Strong phase transitions are preferred over other models and interpretations of the data with a Bayes factor of 8 or more, and in this case, the radius is likely smaller than 12 km. However, radii larger than 12 km are preferred if the neutron stars have uneven temperature distributions.

With the Hubble Frontier Fields program, gravitational lensing has provided a powerful way to extend the study of the ultraviolet luminosity function (LF) of galaxies at |$z$| ∼ 6 down to unprecedented magnitude limits. At the same time, significant discrepancies between different studies were found at the very faint end of the LF. In an attempt to understand such disagreements, we present a comprehensive assessment of the uncertainties associated with the lensing models and the size distribution of galaxies. We use end-to-end simulations from the source plane to the final LF that account for all lensing effects and systematic uncertainties by comparing several mass models. In addition to the size distribution, the choice of lens model leads to large differences at magnitudes fainter than MUV = −15 AB mag, where the magnification factor becomes highly uncertain. We perform Markov Chain Monte Carlo (MCMC) simulations that include all these uncertainties at the individual galaxy level to compute the final LF, allowing, in particular, a crossover between magnitude bins. The best LF…

We present ALMA Band 9 observations of the [C ii]158 |$\mu$|m emission for a sample of 10 main-sequence galaxies at redshift |$z$| ∼ 2, with typical stellar masses (log M⋆/M⊙ ∼ 10.0–10.9) and star formation rates (∼35–115 M⊙ yr−1). Given the strong and well-understood evolution of the interstellar medium from the present to |$z$| = 2, we investigate the behaviour of the [C ii] emission and empirically identify its primary driver. We detect [C ii] from six galaxies (four secure and two tentative) and estimate ensemble averages including non-detections. The [C ii]-to-infrared luminosity ratio (⁠|${\rm [C\, {\small II}]}$|/LIR) of our sample is similar to that of local main-sequence galaxies (∼2 × 10−3), and ∼10 times higher than that of starbursts. The [C ii] emission has an average spatial extent of 4–7 kpc, consistent with the optical size. Complementing our sample with literature data, we find that the [C ii] luminosity correlates with galaxies’ molecular gas mass, with a mean absolute deviation of 0.2 dex and without evident systematics: the [C ii]-to-H2 conversion factor…

Understanding the formation and evolution of our Galaxy requires accurate distances, ages, and chemistry for large populations of field stars. Here, we present several updates to our spectrophotometric distance code, which can now also be used to estimate ages, masses, and extinctions for individual stars. Given a set of measured spectrophotometric parameters, we calculate the posterior probability distribution over a given grid of stellar evolutionary models, using flexible Galactic stellar-population priors. The code (called StarHorse) can accommodate different observational data sets, prior options, partially missing data, and the inclusion of parallax information into the estimated probabilities. We validate the code using a variety of simulated stars as well as real stars with parameters determined from asteroseismology, eclipsing binaries, and isochrone fits to star clusters. Our main goal in this validation process is to test the applicability of the code to field stars with known Gaia-like parallaxes. The typical internal precisions (obtained from realistic simulations of an…

We introduce the the three hundred project, an endeavour to model 324 large galaxy clusters with full-physics hydrodynamical re-simulations. Here we present the data set and study the differences to observations for fundamental galaxy cluster properties and scaling relations. We find that the modelled galaxy clusters are generally in reasonable agreement with observations with respect to baryonic fractions and gas scaling relations at redshift |$z$| = 0. However, there are still some (model-dependent) differences, such as central galaxies being too massive, and galaxy colours (g − r) being bluer (about 0.2 dex lower at the peak position) than in observations. The agreement in gas scaling relations down to |$10^{13}{{\, h^{-1}\, {\rm {M_{\odot }}}}}$| between the simulations indicates that particulars of the sub-grid modelling of the baryonic physics only has a weak influence on these relations. We also include – where appropriate – a comparison to three semi-analytical galaxy formation models as applied to the same underlying dark-matter-only simulation. All simulations and derived…

Wide-field optical surveys have begun to uncover large samples of fast (t rise 5d), luminous (M peak < -18), blue transients.While commonly attributed to the breakout of a supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered detailed investigation of their properties.We present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT 2018cow (ATLAS 18qqn), the first fast-luminous optical transient to be found in real time at low redshift.Our first spectra (< 2 days after discovery) are entirely featureless.A very broad absorption feature suggestive of near-relativistic velocities develops between 3 -8 days, then disappears.Broad emission features of H and He develop after > 10 days.The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R < 10 14 cm after 1 month).This behaviour does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed…

We present N-body simulations of a Sagittarius (Sgr)-like dwarf spheroidal galaxy that follows its orbit about the Milky Way (MW) since its first crossing of the Galaxy’s virial radius to the present day. As Sgr orbits around the MW, it excites vertical oscillations, corrugating and flaring the Galactic stellar disc. These responses can be understood by a two-phase picture in which the interaction is first dominated by torques from the wake excited by Sgr in the MW dark halo before transitioning to tides from Sgr’s direct impact on the disc at late times. We show for the first time that a massive Sgr model simultaneously reproduces the locations and motions of arclike overdensities, such as the Monoceros Ring and the Triangulum Andromeda stellar clouds, that have been observed at the extremities of the disc, while also satisfying the solar-neighbourhood constraints on the vertical structure and streaming motions of the disc. In additional simulations, we include the Large Magellanic Cloud (LMC) self-consistently with Sgr. The LMC introduces coupling through constructive and…

We study the implementation of mechanical feedback from supernovae (SNe) and stellar mass loss in galaxy simulations, within the Feedback In Realistic Environments (FIRE) project. We present the FIRE-2 algorithm for coupling mechanical feedback, which can be applied to any hydrodynamics method (e.g. fixed-grid, moving-mesh, and mesh-less methods), and black hole as well as stellar feedback. This algorithm ensures manifest conservation of mass, energy, and momentum, and avoids imprinting 'preferred directions' on the ejecta. We show that it is critical to incorporate both momentum and thermal energy of mechanical ejecta in a self-consistent manner, accounting for SNe cooling radii when they are not resolved. Using idealized simulations of single SN explosions, we show that the FIRE-2 algorithm, independent of resolution, reproduces converged solutions in both energy and momentum. In contrast, common 'fully-thermal' (energy-dump) or 'fully-kinetic' (particle-kicking) schemes in the literature depend strongly on resolution: when applied at mass resolution >100 solar masses, they…

We develop a new method, which is based on the optimal redshift weighting scheme, to extract the maximal tomographic information of baryonic acoustic oscillations (BAO) and redshift space distortions (RSD) from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 14 quasar (DR14Q) survey. We validate our method using the EZ mocks, and apply our pipeline to the eBOSS DR14Q sample in the redshift range of $0.8

We introduce the Ophiuchus DIsc Survey Employing ALMA (ODISEA), a project aiming to study the entire population of Spitzer-selected protoplanetary discs in the Ophiuchus Molecular Cloud (∼300 objects) from both millimetre continuum and CO isotopologues data. Here we present 1.3 mm/230 GHz continuum images of 147 targets at 0.2 arcsec (28 au) resolution and a typical rms of 0.15 mJy. We detect a total of 133 discs, including the individual components of 11 binary systems and 1 triple system. 60 of these discs are spatially resolved. We find clear substructures (inner cavities, rings, gaps, and/or spiral arms) in eight of the sources and hints of such structures in another four discs. We construct the disc luminosity function for our targets and perform preliminary comparisons to other regions. A simple conversion between flux and dust mass (adopting standard assumptions) indicates that all discs detected at 1.3 mm are massive enough to form one or more rocky planets. In contrast, only ∼50 discs (∼1/3 of the sample) have enough mass in the form of dust to form the canonical 10 M⊕ core…

ABSTRACT The detection of the binary neutron star merger GW170817 together with the observation of electromagnetic counterparts across the entire spectrum inaugurated a new era of multimessenger astronomy. In this study, we incorporate wavelength-dependent opacities and emissivities calculated from atomic-structure data enabling us to model both the measured light curves and spectra of the electromagnetic transient AT2017gfo. Best fits of the observational data are obtained by Gaussian Process Regression, which allows us to present posterior samples for the kilonova and source properties connected to GW170817. Incorporating constraints obtained from the gravitational wave signal measured by the LIGO-Virgo Scientific Collaboration, we present a $90{{\ \rm per\ cent}}$ upper bound on the mass ratio q ≲ 1.38 and a lower bound on the tidal deformability of $\tilde{\Lambda } \gtrsim 197$, which rules out sufficiently soft equations of state. Our analysis is a path-finder for more realistic kilonova models and shows how the combination of gravitational wave and electromagnetic…

We present a model for the concurrent formation of globular clusters (GCs) and supermassive stars (SMSs, 10 3 M ) to address the origin of the HeCNONaMgAl abundance anomalies in GCs.GCs form in converging gas flows and accumulate low-angular momentum gas, which accretes on to protostars.This leads to an adiabatic contraction of the cluster and an increase of the stellar collision rate.A SMS can form via runaway collisions if the cluster reaches sufficiently high density before two-body relaxation halts the contraction.This condition is met if the number of stars 10 6 and the gas accretion rate 10 5 M Myr -1 , reminiscent of GC formation in high gas-density environments, such as -but not restricted to -the early Universe.The strong SMS wind mixes with the inflowing pristine gas, such that the protostars accrete diluted hot-hydrogen burning yields of the SMS.Because of continuous rejuvenation, the amount of processed material liberated by the SMS can be an order of magnitude higher than its maximum mass.This 'conveyor-belt' production of hot-hydrogen burning products provides a…

The electromagnetic transients accompanying compact binary mergers (γ -ray bursts, afterglows and 'macronovae') are crucial to pinpoint the sky location of gravitational wave sources.Macronovae are caused by the radioactivity from freshly synthesized heavy elements, e.g. from dynamic ejecta and various types of winds.We study macronova signatures by using multidimensional radiative transfer calculations.We employ the radiative transfer code SUPERNU and state-of-the-art LTE opacities for a few representative elements from the wind and dynamical ejecta (Cr, Pd, Se, Te, Br, Zr, Sm, Ce, Nd, U) to calculate synthetic light curves and spectra for a range of ejecta morphologies.The radioactive power of the resulting macronova is calculated with the detailed input of decay products.We assess the detection prospects for our most complex models, based on the portion of viewing angles that are sufficiently bright, at different cosmological redshifts (z).The brighter emission from the wind is unobscured by the lanthanides (or actinides) in some of the models, permitting non-zero detection…

Recent work, based on data from the Hubble Space Telescope (HST) UV Legacy Survey of Galactic Globular Clusters (GCs), has revealed that all the analyzed clusters host two groups of first- (1G) and second-generation (2G) stars. In most GCs, both 1G and 2G stars host sub-stellar populations with different chemical composition. We compare multi-wavelength HST photometry with synthetic spectra to determine for the first time the average helium difference between the 2G and 1G stars in a large sample of 57 GCs and the maximum helium variation within each of them. We find that in all clusters 2G stars are consistent with being enhanced in helium with respect to 1G. The maximum helium variation ranges from less than 0.01 to more than 0.10 in helium mass fraction and correlates with both the cluster mass and the color extension of the horizontal branch (HB). These findings demonstrate that the internal helium variation is one of the main (second) parameters governing the HB morphology.

Transmission spectroscopy of exoplanets has the potential to provide precise measurements of atmospheric chemical abundances, in particular of hot Jupiters whose large sizes and high temperatures make them conducive to such observations. To date, several transmission spectra of hot Jupiters have revealed low amplitude features of water vapour compared to expectations from cloud-free atmospheres of solar metallicity. The low spectral amplitudes in such atmospheres could either be due to the presence of aerosols that obscure part of the atmosphere or due to inherently low abundances of H2O in the atmospheres. A recent survey of transmission spectra of ten hot Jupiters used empirical metrics to suggest atmospheres with a range of cloud/haze properties but with no evidence for H2O depletion. Here, we conduct a detailed and homogeneous atmospheric retrieval analysis of the entire sample and report the H2O abundances, cloud properties, terminator temperature profiles, and detection significances of the chemical species. This study finds that the majority of hot Jupiters have atmospheres…

We present predictions for the quenching of star formation in satellite galaxies of the Local Group from a suite of 30 cosmological zoom simulations of Milky Way-like host galaxies. The Auriga simulations resolve satellites down to the luminosity of the classical dwarf spheroidal galaxies of the Milky Way. We find strong mass-dependent and distance-dependent quenching signals, where dwarf systems beyond 600 kpc are only strongly quenched below a stellar mass of 107 M⊙. Ram pressure stripping appears to be the dominant quenching mechanism and 50 per cent of quenched systems cease star formation within 1 Gyr of first infall. We demonstrate that systems within a host galaxy’s R200 radius are comprised of two populations: (i) a first infall population that has entered the host halo within the past few Gyrs and (ii) a population of returning ‘backsplash’ systems that have had a much more extended interaction with the host. Backsplash galaxies that do not return to the host galaxy by redshift zero exhibit quenching properties similar to galaxies within R200 and are distinct from other…

Six gravitational wave detections have been reported so far, providing crucial insights on the merger rate of double compact objects. We investigate the cosmic merger rate of double neutron stars (DNSs), neutron star black hole binaries (NSBHs), and black hole binaries (BHBs) by means of population-synthesis simulations coupled with the Illustris cosmological simulation. We have performed six different simulations, considering different assumptions for the efficiency of common envelope (CE) ejection and exploring two distributions for the supernova (SN) kicks. The current BHB merger rate derived from our simulations spans from ∼150 to ∼240 Gpc−3 yr−1 and is only mildly dependent on CE efficiency. In contrast, the current merger rates of DNSs (ranging from ∼20 to ∼600 Gpc−3 yr−1) and NSBHs (ranging from ∼10 to ∼100 Gpc−3 yr−1) strongly depend on the assumptions on CE and natal kicks. The merger rate of DNSs is consistent with the one inferred from the detection of GW170817 only if a high efficiency of CE ejection and low-SN kicks (drawn from a Maxwellian distribution with…

We introduce a value-added full-sky catalogue of galaxies, named as Galaxy List for the Advanced Detector Era, or GLADE. The purpose of this catalogue is to (i) help identifications of host candidates for gravitational-wave events, (ii) support target selections for electromagnetic follow-up observations of gravitational-wave candidates, (iii) provide input data on the matter distribution of the local Universe for astrophysical or cosmological simulations, and (iv) help identifications of host candidates for poorly localized electromagnetic transients, such as gamma-ray bursts observed with the InterPlanetary Network. Both being potential hosts of astrophysical sources of gravitational waves, GLADE includes inactive and active galaxies as well. GLADE was constructed by cross-matching and combining data from five separate (but not independent) astronomical catalogues: GWGC, 2MPZ, 2MASS XSC, HyperLEDA, and SDSS-DR12Q. GLADE is complete up to |$d_{\rm L}=37^{+3}_{-4}\, \mathrm{Mpc}$| in terms of the cumulative B-band luminosity of galaxies within luminosity distance dL, and contains…

Deep learning with artificial neural networks is increasingly gaining attention, because of its potential for data-driven astronomy. However, this methodology usually does not provide uncertainties and does not deal with incompleteness and noise in the training data. In this work, we design a neural network for high-resolution spectroscopic analysis using APOGEE data that mimics the methodology of standard spectroscopic analyses: stellar parameters are determined using the full wavelength range, but individual element abundances use censored portions of the spectrum. We train this network with a customized objective function that deals with incomplete and noisy training data and apply dropout variational inference to derive uncertainties on our predictions. We determine parameters and abundances for 18 individual elements at the $\approx 0.03$ dex level, even at low signal-to-noise ratio. We demonstrate that the uncertainties returned by our method are a realistic estimate of the precision and they automatically blow up when inputs or outputs outside of the training set are…

We present two galaxy shape catalogues from the Dark Energy Survey Year 1 data set, covering 1500 deg2 with a median redshift of 0.59. The catalogues cover two main fields: Stripe 82, and an area overlapping the South Pole Telescope survey region. We describe our data analysis process and in particular our shape measurement using two independent shear measurement pipelines, metacalibration and im3shape. The metacalibration catalogue uses a Gaussian model with an innovative internal calibration scheme, and was applied to riz bands, yielding 34.8M objects. The im3shape catalogue uses a maximum-likelihood bulge/disc model calibrated using simulations, and was applied to r-band data, yielding 21.9M objects. Both catalogues pass a suite of null tests that demonstrate their fitness for use in weak lensing science. We estimate the 1σ uncertainties in multiplicative shear calibration to be 0.013 and 0.025 for the metacalibration and im3shape catalogues, respectively.

We describe the derivation and validation of redshift distribution estimates and their uncertainties for the populations of galaxies used as weak-lensing sources in the Dark Energy Survey (DES) Year 1 cosmological analyses. The Bayesian Photometric Redshift (bpz) code is used to assign galaxies to four redshift bins between z ≈ 0.2 and ≈1.3, and to produce initial estimates of the lensing-weighted redshift distributions |$n^i_{\rm PZ}(z)\propto \mathrm{d}n^i/\mathrm{d}z$| for members of bin i. Accurate determination of cosmological parameters depends critically on knowledge of ni, but is insensitive to bin assignments or redshift errors for individual galaxies. The cosmological analyses allow for shifts |$n^i(z)=n^i_{\rm PZ}(z-\Delta z^i)$| to correct the mean redshift of ni(z) for biases in |$n^i_{\rm PZ}$|⁠. The Δzi are constrained by comparison of independently estimated 30-band photometric redshifts of galaxies in the Cosmic Evolution Survey (COSMOS) field to bpz estimates made from the DES griz fluxes, for a sample matched in fluxes, pre-seeing size, and lensing weight to the…

The short Gamma-Ray Burst, GRB 170817A, that followed the binary neutron star merger gravitational waves signal, GW170817, is not a usual short gamma-ray burst (sGRB). It is weaker by three orders of magnitude than the weakest sGRB seen before and its spectrum, showing a hard early signal followed by a softer thermal spectrum, is unique. We show, first, that the γ-rays must have emerged from at least mildly relativistic outflow, implying that a relativistic jet was launched following the merger. We then show that the observations are consistent with the predictions of a mildly relativistic shock breakout: a minute γ-ray energy as compared with the total energy and a rather smooth light curve with a hard to soft evolution. We present here a novel analytic study and detailed numerical 2D and 3D relativistic hydrodynamic and radiation simulations that support the picture in which the observed γ-rays arose from a shock breakout of a cocoon from the merger’s ejecta . The cocoon can be formed either by a choked jet which does not generate an sGRB (in any direction) or by a successful jet…

We present a semi-empirical, largely model-independent approach for estimating Galactic birth radii, rbirth, for Milky Way disc stars. The technique relies on the justifiable assumption that a negative radial metallicity gradient in the interstellar medium (ISM) existed for most of the disc lifetime. Stars are projected back to their birth positions according to the observationally derived age and [Fe/H] with no kinematical information required. Applying our approach to the AMBRE:HARPS and HARPS–GTO local samples, we show that we can constrain the ISM metallicity evolution with Galactic radius and cosmic time, [Fe/H]ISM(r, t), by requiring a physically meaningful rbirth distribution. We find that the data are consistent with an ISM radial metallicity gradient that flattens with time from ∼− 0.15 dex kpc−1 at the beginning of disc formation, to its measured present-day value (−0.07 dex kpc−1). We present several chemokinematical relations in terms of mono-rbirth populations. One remarkable result is that the kinematically hottest stars would have been born locally or in the outer…

Ultracompact binaries with orbital periods less than a few hours will dominate the gravitational wave signal in the mHz regime. Until recently, 10 systems were expected to have a predicted gravitational wave signal strong enough to be detectable by the Laser Interferometer Space Antenna (LISA), the so-called ‘verification binaries’. System parameters, including distances, are needed to provide an accurate prediction of the expected gravitational wave strength to be measured by LISA. Using parallaxes from Gaia Data Release 2 we calculate signal-to-noise ratios (SNR) for ≈50 verification binary candidates. We find that 11 binaries reach an SNR ≥ 20, two further binaries reaching an SNR≥ 5, and three more systems are expected to have a SNR≈ 5 after 4 yr integration with LISA. For these 16 systems, we present predictions of the gravitational wave amplitude (⁠|$\mathcal {A}$|⁠) and parameter uncertainties from Fisher information matrix on the amplitude (⁠|$\mathcal {A}$|⁠) and inclination (ι).

We present measurements of the mean and scatter of the intergalactic medium (IGM) Lyman-α opacity at 4.9 < z < 6.1 along the lines of sight of 62 quasars at zsource> 5.7, the largest sample assembled at these redshifts to date by a factor of two. The sample size enables us to sample cosmic variance at these redshifts more robustly than ever before. The spectra used here were obtained by the Sloan Digital Sky Survey, Dark Energy Survey–VISTA Hemisphere Survey, and Subaru High-z Exploration of Low-Luminosity Quasars collaborations, drawn from the Echellette Spectrograph and Imager and X-Shooter archives, reused from previous studies or observed specifically for this work. We measure the effective optical depth of Lyman-α in bins of 10, 30, 50, and 70 cMpc h−1, construct cumulative distribution functions under two treatments of upper limits on flux and explore an empirical analytic fit to residual Lyman-α transmission. We verify the consistency of our results with those of previous studies via bootstrap resampling and confirm the existence of tails towards high values in the opacity…

We present a sample of 40 active galactic nucleus (AGN) in dwarf galaxies at redshifts z ≲ 2.4. The galaxies are drawn from the Chandra COSMOS-Legacy survey as having stellar masses 107 ≤ M* ≤ 3 × 109 M⊙. Most of the dwarf galaxies are star forming. After removing the contribution from star formation to the X-ray emission, the AGN luminosities of the 40 dwarf galaxies are in the range L0.5–10 keV ∼ 1039−1044 erg s−1. With 12 sources at z > 0.5, our sample constitutes the highest-redshift discovery of AGN in dwarf galaxies. The record-holder is cid_1192, at z = 2.39 and with L0.5–10 keV ∼ 1044 erg s−1. One of the dwarf galaxies has M* = 6.6 × 107 M⊙ and is the least massive galaxy found so far to host an AGN. All the AGN are of type 2 and consistent with hosting intermediate-mass black holes (BHs) with masses ∼104–105 M⊙ and typical Eddington ratios >1 per cent. We also study the evolution, corrected for completeness, of AGN fraction with stellar mass, X-ray luminosity, and redshift in dwarf galaxies out to z = 0.7. We find that the AGN fraction for 109 < M* ≤ 3 × 109 M⊙ and LX ∼…

We present a suite of cosmological zoom-in simulations at z ≥ 5 from the Feedback In Realistic Environments project, spanning a halo mass range Mhalo ∼ 108–1012 M⊙ at z = 5. We predict the stellar mass–halo mass relation, stellar mass function, and luminosity function in several bands from z = 5 to 12. The median stellar mass–halo mass relation does not evolve strongly at z = 5–12. The faint-end slope of the luminosity function steepens with increasing redshift, as inherited from the halo mass function at these redshifts. Below z ∼ 6, the stellar mass function and ultraviolet (UV) luminosity function slightly flatten below M* ∼ 104.5 M⊙ (fainter than M1500 ∼ −12), owing to the fact that star formation in low-mass haloes is suppressed by the ionizing background by the end of reionization. Such flattening does not appear at higher redshifts. We provide redshift-dependent fitting functions for the SFR–Mhalo, SFR–M*, and broad-band magnitude–stellar mass relations. We derive the star formation rate density and stellar mass density at z = 5–12 and show that the contribution from very…

We present a panoramic map of the stellar streams of the Milky Way based upon astrometric and photometric measurements from the Gaia DR2 catalogue. In this first contribution, we concentrate on the halo at heliocentric distances beyond |$5{\rm \, kpc}$|⁠, and at Galactic latitudes |b| > 30°, using the STREAMFINDER algorithm to detect structures along plausible orbits that are consistent with the Gaia proper motion measurements. We find a rich network of criss-crossing streams in the halo. Some of these structures were previously known, while several are new discoveries, but others are potentially artefacts of the Gaia scanning law and will require confirmation. With these initial discoveries, we are starting to unravel the complex formation of the halo of our Galaxy.

We explore the abundance, spatial distribution, and physical properties of the OVI, OVII, and OVIII ions of oxygen in circumgalactic and intergalactic media (the CGM, IGM, and WHIM). We use the TNG100 and TNG300 large volume cosmological magneto-hydrodynamical simulations. Modeling the ionization states of simulated oxygen, we find good agreement with observations of the low-redshift OVI column density distribution function (CDDF), and present its evolution for all three ions from z=0 to z=4. Producing mock quasar absorption line spectral surveys, we show that the IllustrisTNG simulations are fully consistent with constraints on the OVI content of the CGM from COS-Halos and other low redshift observations, producing columns as high as observed. We measure the total amount of mass and average column densities of each ion using hundreds of thousands of simulated galaxies spanning 10^11 < Mhalo/Msun < 10^15 corresponding to 10^9 < M*/Msun < 10^12 in stellar mass. Stacked radial profiles of OVI are computed in 3D number density and 2D projected column, decomposing into the 1-halo and…

In this paper we present the astro-photometric catalogues of 56 globular clusters and one open cluster. Astrometry and photometry are mainly based on images collected within the "HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation" (GO-13297, PI:~Piotto), and the "ACS Survey of Galactic Globular Clusters" (GO-10775, PI:~Sarajedini). For each source in the catalogues for which we have reliable proper motion we also publish a membership probability for separation of field and cluster stars. These new catalogues, which we make public in Mikulski Archive for Space Telescopes, replace previous catalogues by Paper VIII of this series.

The theory of the nuclear energy-density functional is used to provide a unified and thermodynamically consistent treatment of all regions of cold non-accreting neutron stars. In order to assess the impact of our lack of complete knowledge of the density dependence of the symmetry energy on the constitution and the global structure of neutron stars, we employ four different functionals. All of them were precision fitted to essentially all the nuclear-mass data with the Hartree-Fock-Bogoliubov method and two different neutron-matter equations of state based on realistic nuclear forces. For each functional, we calculate the composition, the pressure-density relation, and the chemical potentials throughout the star. We show that uncertainties in the symmetry energy can significantly affect the theoretical results for the composition and global structure of neutron stars. To facilitate astrophysical applications, we construct analytic fits to our numerical results.

ABSTRACT We present angular diameter distance measurements obtained by locating the baryon acoustic oscillations (BAO) scale in the distribution of galaxies selected from the first year of Dark Energy Survey data. We consider a sample of over 1.3 million galaxies distributed over a footprint of 1336 deg2 with 0.6 < $z$photo < 1 and a typical redshift uncertainty of 0.03(1 + $z$). This sample was selected, as fully described in a companion paper, using a colour/magnitude selection that optimizes trade-offs between number density and redshift uncertainty. We investigate the BAO signal in the projected clustering using three conventions, the angular separation, the comoving transverse separation, and spherical harmonics. Further, we compare results obtained from template-based and machine-learning photometric redshift determinations. We use 1800 simulations that approximate our sample in order to produce covariance matrices and allow us to validate our distance scale measurement methodology. We measure the angular diameter distance, DA, at the effective redshift of our sample divided…

In this paper, we present the results of our three-dimensional, multigroup, multineutrino-species radiation/hydrodynamic simulation using the state-of-the-art code fornax of the terminal dynamics of the core of a non-rotating 16 M⊙ stellar progenitor. The calculation incorporates redistribution by inelastic scattering, a correction for the effect of many-body interactions on the neutrino–nucleon scattering rates, approximate general relativity (including the effects of gravitational redshifts), velocity-dependent frequency advection, and an implementation of initial perturbations in the progenitor core. The model explodes within ∼100 ms of bounce (near when the silicon–oxygen interface is accreted through the temporarily stalled shock) and by the end of the simulation (here, ∼677 ms after bounce) is accumulating explosion energy at a rate of ∼2.5 × 1050 erg s−1. The supernova explodes with an asymmetrical multiplume structure, with one hemisphere predominating. The gravitational mass of the residual proto-neutron star at ∼677 ms is ∼1.42 M⊙. Even at the end of the simulation,…

We introduce ProFound, a source finding and image analysis package. ProFound provides methods to detect sources in noisy images, generate segmentation maps identifying the pixels belonging to each source, and measure statistics like flux, size, and ellipticity. These inputs are key requirements of ProFit, our recently released galaxy profiling package, where the design aim is that these two software packages will be used in unison to semi-automatically profile large samples of galaxies. The key novel feature introduced in ProFound is that all photometry is executed on dilated segmentation maps that fully contain the identifiable flux, rather than using more traditional circular or ellipse-based photometry. Also, to be less sensitive to pathological segmentation issues, the de-blending is made across saddle points in flux. We apply ProFound in a number of simulated and real-world cases, and demonstrate that it behaves reasonably given its stated design goals. In particular, it offers good initial parameter estimation for ProFit, and also segmentation maps that follow the sometimes…

Accurate cosmology from upcoming weak lensing surveys relies on knowledge of the total matter power spectrum at per cent level at scales k < 10 h Mpc−1, for which modelling the impact of baryonic physics is crucial. We compare measurements of the total matter power spectrum from the Horizon cosmological hydrodynamical simulations: a dark-matter-only run, one with full baryonic physics, and another lacking active galactic nucleus (AGN) feedback. Baryons cause a suppression of power at k ≃ 10 h Mpc−1 of |${\lt}15{{\ \rm per\ cent}}$| at |$z$| = 0, and an enhancement of a factor of a few at smaller scales due to the more efficient cooling and star formation. The results are sensitive to the presence of the highest mass haloes in the simulation and the distribution of dark matter is also impacted up to a few per cent. The redshift evolution of the effect is non-monotonic throughout |$z$| = 0−5 due to an interplay between AGN feedback and gas pressure, and the growth of structure. We investigate the effectiveness of an analytic ‘baryonic correction model’ in describing our results. We…

We test if the cosmological zoom-in simulations of isolated galaxies from the FIRE project reproduce the properties of ultra diffuse galaxies (UDGs). We show that outflows that dynamically heat galactic stars, together with a passively aging stellar population after imposed quenching, naturally reproduce the observed population of red UDGs, without the need for high spin haloes, or dynamical influence from their host cluster. We reproduce the range of surface brightness, radius, and absolute magnitude of the observed red UDGs by quenching simulated galaxies at a range of different times. They represent a mostly uniform population of dark matter-dominated dwarf galaxies with M* ∼ 108 M⊙, low metallicity, and a broad range of ages; the more massive the UDGs, the older they are. The most massive red UDG in our sample (M* ∼ 3 × 108 M⊙) requires quenching at z ∼ 3 when its halo reached Mh ∼ 1011 M⊙. Our simulated UDGs form with normal stellar-to-halo ratios and match the central enclosed masses and the velocity dispersions of the observed UDGs. Enclosed masses remain largely fixed across…

We present 3D hydrodynamical models of the HD 142527 protoplanetary disc, a bright and well-studied disc that shows spirals and shadows in scattered light around a 100 au gas cavity, a large horseshoe dust structure in mm continuum emission, together with mysterious fast radial flows and streamers seen in gas kinematics. By considering several possible orbits consistent with the observed arc, we show that all of the main observational features can be explained by one mechanism – the interaction between the disc and the observed binary companion. We find that the spirals, shadows, and horseshoe are only produced in the correct position angles by a companion on an inclined and eccentric orbit approaching periastron – the ‘red’ family from Lacour et al. Dust–gas simulations show radial and azimuthal concentration of dust around the cavity, consistent with the observed horseshoe. The success of this model in the HD 142527 disc suggests other mm-bright transition discs showing cavities, spirals, and dust asymmetries may also be explained by the interaction with central companions.

We present a simple analytic model, that captures the key features of the emission of radiation from material ejected by the merger of neutron stars (NS), and construct the multi-band and bolometric luminosity light curves of the transient associated with GW170817, AT\,2017gfo, using all available data. The UV to IR emission is shown to be consistent with a single $\approx0.05$\,M$_\odot$ component ejecta, with a power-law velocity distribution between $\approx 0.1\,c$ and $>0.3\,c$, a low opacity, {$κ<1$\,cm$^2$\,g$^{-1}$}, and a radioactive energy release rate consistent with an initial $Y_{\rm e}<0.4$. The late time spectra require an opacity of $κ_ν\approx0.1$\,cm$^2$\,g$^{-1}$ at 1 to $2μ$m. If this opacity is provided entirely by Lanthanides, their implied mass fraction is $X_{\rm Ln}\approx10^{-3}$, approximately 30 times below the value required to account for the solar abundance. The inferred value of $X_{\rm Ln}$ is uncertain due to uncertainties in the estimates of IR opacities of heavy elements, which also do not allow the exclusion of a significant contribution to the…

In this paper, we study the strong gravitational lensing of gravitational waves (GWs) from a statistical perspective, with particular focus on the high frequency GWs from stellar binary black hole coalescences. These are most promising targets for ground-based detectors such as Advanced Laser Interferometer Gravitational Wave Observatory (aLIGO) and the proposed Einstein Telescope (ET) and can be safely treated under the geometrical optics limit for GW propagation. We perform a thorough calculation of the lensing rate, by taking account of effects caused by the ellipticity of lensing galaxies, lens environments, and magnification bias. We find that in certain GW source rate scenarios, we should be able to observe strongly lensed GW events once per year (∼1 yr−1) in the aLIGO survey at its design sensitivity; for the proposed ET survey, the rate could be as high as ∼80 yr−1. These results depend on the estimate of GW source abundance, and hence can be correspondingly modified with an improvement in our understanding of the merger rate of stellar binary black holes. We also compute…

Radio emission is a key indicator of star formation activity in galaxies, but the radio luminositystar formation relation has to date been studied almost exclusively at frequencies of 1.4 GHz or above.At lower radio frequencies, the effects of thermal radio emission are greatly reduced, and so we would expect the radio emission observed to be completely dominated by synchrotron radiation from supernova-generated cosmic rays.As part of the LOFAR Surveys Key Science project, the Herschel-ATLAS NGP field has been surveyed with LOFAR at an effective frequency of 150 MHz.We select a sample from the MPA-JHU catalogue of Sloan Digital Sky Survey galaxies in this area: the combination of Herschel, optical and mid-infrared data enable us to derive star formation rates (SFRs) for our sources using spectral energy distribution fitting, allowing a detailed study of the low-frequency radio luminosity-star formation relation in the nearby Universe.For those objects selected as star-forming galaxies (SFGs) using optical emission line diagnostics, we find a tight relationship between the 150 MHz…

We present a suite of 3D multiphysics MHD simulations following star formation in isolated turbulent molecular gas discs ranging from 5 to 500 parsecs in radius. These simulations are designed to survey the range of surface densities between those typical of Milky Way giant molecular clouds (GMCs) (⁠|${\sim } 10^2\,{\rm {\rm M}_{\odot }\,pc^{-2}}$|⁠) and extreme ultraluminous infrared galaxy environments (⁠|${\sim } 10^4\,{\rm {\rm M}_{\odot }\,pc^{-2}}$|⁠) so as to map out the scaling of the cloud-scale star formation efficiency (SFE) between these two regimes. The simulations include prescriptions for supernova, stellar wind, and radiative feedback, which we find to be essential in determining both the instantaneous per-freefall (εff) and integrated (εint) star formation efficiencies. In all simulations, the gas discs form stars until a critical stellar surface density has been reached and the remaining gas is blown out by stellar feedback. We find that surface density is a good predictor of εint, as suggested by analytic force balance arguments from previous works. SFE eventually…

We show that nearly half of all binary black hole (BBH) mergers dynamically assembled in globular clusters have measurable eccentricities (e > 0.01) in the LISA band (10−2 Hz), when General Relativistic corrections are properly included in the N-body evolution. If only Newtonian gravity is included, the derived fraction of eccentric LISA sources is significantly lower, which explains why recent studies all have greatly underestimated this fraction. Our findings have major implications for how to observationally distinguish between BBH formation channels using eccentricity with LISA, which is one of the key science goals of the mission. We illustrate that the relatively large population of eccentric LISA sources reported here originates from BBHs that merge between hardening binary–single interactions inside their globular cluster. These results indicate a bright future for using LISA to probe the origin of BBH mergers.

In anticipation of the upcoming deployment of the James Webb Space Telescope (JWST), we present high-redshift predictions by the well-established Santa Cruz semi-analytic model. We update the models by re-calibrating them after adopting cosmological parameters consistent with recent constraints from Planck. We provide predictions for rest-frame UV luminosity functions for galaxy populations over a wide range of $M_\text{UV}$ from $\sim-6$ to $\sim-24$ between $z = 4 - 10$. In addition, we present the corresponding predictions for observed-frame galaxy number counts in different redshift bins in the full set of NIRCam filters. We provide predictions of the quantitative effect on these observables of varying the physical recipes implemented in the models, such as the molecular gas depletion time (star formation efficiency) scalings or the scalings of outflow rates driven by stars and supernovae with galaxy circular velocity. Based on these results, we discuss what may be learned about the physical processes that shape galaxy formation from JWST observations of galaxy number densities…

We provide here a significant extension of the NuGrid Set 1 models in mass coverage and towards lower metallicity, adopting the same physics assumptions.The combined data set now includes the initial masses M ZAMS / M = 1, 1. 65, 2, 3, 4, 5, 6, 7, 12, 15, 20, 25 for Z = 0.02, 0.01, 0.006, 0.001, 0.0001 with α-enhanced composition for the lowest three metallicities.These models are computed with the MESA stellar evolution code and are evolved up to the AGB, the white dwarf stage, or until core collapse.The nucleosynthesis was calculated for all isotopes in post-processing with the NuGrid MPPNP code.Explosive nucleosynthesis is based on semi-analytic 1D shock models.Metallicity-dependent mass-loss, convective boundary mixing in low-and intermediate-mass models and H and He core burning massive star models are included.Convective O-C shell mergers in some stellar models lead to the strong production of odd-Z elements P, Cl, K, and Sc.In AGB models with hot dredge-up, the convective boundary mixing efficiency is reduced to accommodate for its energetic feedback.In both low-mass and…

Most stars form and spend their early life in regions of enhanced stellar density. Therefore, the evolution of protoplanetary discs (PPDs) hosted by such stars are subject to the influence of other members of the cluster. Physically, PPDs might be truncated either by photoevaporation due to ultraviolet flux from massive stars, or tidal truncation due to close stellar encounters. Here we aim to compare the two effects in real cluster environments. In this vein we first review the properties of well-studied stellar clusters with a focus on stellar number density, which largely dictates the degree of tidal truncation, and far-ultraviolet (FUV) flux, which is indicative of the rate of external photoevaporation. We then review the theoretical PPD truncation radius due to an arbitrary encounter, additionally taking into account the role of eccentric encounters that play a role in hot clusters with a 1D velocity dispersion σv ≳ 2 km s−1. Our treatment is then applied statistically to varying local environments to establish a canonical threshold for the local stellar density (nc ≳ 104 pc−3)…

We study radial profiles in H α equivalent width and specific star formation rate (sSFR) derived from spatially resolved SDSS-IV MaNGA spectroscopy to gain insight on the physical mechanisms that suppress star formation and determine a galaxy’s location in the SFR-M⋆ diagram. Even within the star-forming ‘main sequence’, the measured sSFR decreases with stellar mass, in both an integrated and spatially resolved sense. Flat sSFR radial profiles are observed for log(M⋆/M⊙) < 10.5, while star-forming galaxies of higher mass show a significant decrease in sSFR in the central regions, a likely consequence of both larger bulges and an inside-out growth history. Our primary focus is the green valley, constituted by galaxies lying below the star formation main sequence, but not fully passive. In the green valley we find sSFR profiles that are suppressed with respect to star-forming galaxies of the same mass at all galactocentric distances out to 2 effective radii. The responsible quenching mechanism therefore appears to affect the entire galaxy, not simply an expanding central region. The…

We present the dissection in space, time, and energy of the region around the IceCube-170922A neutrino alert. This study is motivated by: (1) the first association between a neutrino alert and a blazar in a flaring state, TXS 0506+056; (2) the evidence of a neutrino flaring activity during 2014–2015 from the same direction; (3) the lack of an accompanying simultaneous γ-ray enhancement from the same counterpart; (4) the contrasting flaring activity of a neighbouring bright γ-ray source, the blazar PKS 0502+049, during 2014–2015. Our study makes use of multiwavelength archival data accessed through Open Universe tools and includes a new analysis of Fermi-LAT data. We find that PKS 0502+049 contaminates the γ-ray emission region at low energies but TXS 0506+056 dominates the sky above a few GeV. TXS 0506+056, which is a very strong (top percent) radio and γ-ray source, is in a high γ-ray state during the neutrino alert but in a low though hard γ-ray state in coincidence with the neutrino flare. Both states can be reconciled with the energy associated with the neutrino emission and, in…

The role of galaxy mergers in fuelling active galactic nuclei (AGNs) is still debated, owing partly to selection effects inherent to studies of the merger/AGN connection. In particular, luminous AGNs are often obscured in late-stage mergers. Mid-infrared (IR) colour selection of dust-enshrouded AGN with, e.g. the Wide-field Infrared Survey Explorer (WISE) has uncovered large new populations of obscured AGN. However, this method is sensitive mainly to AGN that dominate emission from the host. To understand how selection biases affect mid-IR studies of the merger/AGN connection, we simulate the evolution of AGN throughout galaxy mergers. Although mid-IR colours closely trace luminous, obscured AGN, we show that nearly half of merger-triggered AGNs are missed with common mid-IR selection criteria, even in late-stage, gas-rich major mergers. At z ≲ 0.5, where merger signatures and dual nuclei can most easily be detected, we find that a more lenient W1 − W2 > 0.5 cut greatly improves completeness without significantly decreasing reliability. Extreme nuclear starbursts are briefly able to…

We present the most precise measurement of the z = 0 H i mass function (HIMF) to date based on the final catalogue of the ALFALFA (Arecibo Legacy Fast ALFA) blind H i survey of the nearby Universe. The Schechter function fit has a ‘knee’ mass |$\log (M_{*}\,h^{2}_{70}/\mathrm{M_{{\odot }}}) = 9.94 \pm 0.01 \pm 0.05$|⁠, a low-mass slope parameter α = −1.25 ± 0.02 ± 0.1, and a normalization |$\phi _{*} = (4.5 \,\pm \, 0.2\, \pm \, 0.8) \times 10^{-3} \, h^{3}_{70}\, \mathrm{Mpc^{-3}\,dex^{-1}}$|⁠, with both random and systematic uncertainties as quoted. Together these give an estimate of the H i content of the z = 0 Universe as |$\Omega _{\mathrm{\rm{H\,\small {I}}}} = (3.9 \pm 0.1 \pm 0.6) \times 10^{-4} \, h^{-1}_{70}$| (corrected for H i self-absorption). Our analysis of the uncertainties indicates that the ‘knee’ mass is a cosmologically fair measurement of the z = 0 value, with its largest uncertainty originating from the absolute flux calibration, but that the low-mass slope is only representative of the local Universe. We also explore large-scale trends in α and M* across the…

We report results from 21-cm intensity maps acquired from the Parkes radio telescope and cross-correlated with galaxy maps from the 2dF galaxy survey. The data span the redshift range 0.057 < z < 0.098 and cover approximately 1300 deg2 over two long fields. Cross-correlation is detected at a significance of 5.7 σ. The amplitude of the cross-power spectrum is low relative to the expected dark matter power spectrum, assuming a neutral hydrogen (H i) bias and mass density equal to measurements from the ALFALFA survey. The decrement is pronounced and statistically significant at small scales. At k ∼ 1.5 h Mpc−1, the cross-power spectrum is more than a factor of 6 lower than expected, with a significance of 15.3 σ. This decrement indicates a lack of clustering of neutral hydrogen (H i), a small correlation coefficient between optical galaxies and H i, or some combination of the two. Separating 2dF into red and blue galaxies, we find that red galaxies are much more weakly correlated with H i on k ∼ 1.5 h Mpc−1 scales, suggesting that H i is more associated with blue star-forming galaxies…

It is well known that galaxies falling into clusters can experience gas stripping due to ram pressure by the intra-cluster medium. The most spectacular examples are galaxies with extended tails of optically bright stripped material known as ‘jellyfish’. We use the first large homogeneous compilation of jellyfish galaxies in clusters from the WINGS and OmegaWINGS surveys, and follow-up MUSE observations from the GASP MUSE programme to investigate the orbital histories of jellyfish galaxies in clusters and reconstruct their stripping history through position versus velocity phase-space diagrams. We construct analytic models to define the regions in phase-space where ram-pressure stripping is at play. We then study the distribution of cluster galaxies in phase-space and find that jellyfish galaxies have on average higher peculiar velocities (and higher cluster velocity dispersion) than the overall population of cluster galaxies at all cluster-centric radii, which is indicative of recent infall into the cluster and radial orbits. In particular, the jellyfish galaxies with the longest…