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This paper presents the results of the analysis of the integrated-light spectra of eight Galactic globular clusters with a relatively low luminosity and stellar density: Palomar 1, Palomar 2, Palomar 10, Palomar 13, Palomar 14, NGC 6426, NGC 6535, and NGC 6749. The absorption spectral indices in the Lick system were measured in their spectra, as well as in the spectra of bright clusters: NGC 7006, NGC 6229, NGC 6779, NGC 6205, NGC 6341, and NGC 2419. The age, metallicity, and approximate abundance of the $$\alpha $$ -process elements were determined for eight objects under study. The material of the study was the archival observational data of the 1.93-m telescope of the Haute-Provence Observatory. For seven out of eight objects, galactic analogs with close values of the Lick indices within the limits of their determination errors were found. The coincidence of the Lick indices implies the similarity of age and chemical composition. The available literature data confirm our conclusions regarding the similarity of the properties of the clusters’ stellar populations. According to the literature data on the spatial position and motion of objects, the objects of study turned out to belong, as a rule, to the same subsystems of the Galaxy as their analogs. No globular clusters with a complete set of Lick indices similar to those of Palomar 1 were found, which supports the literature conclusions about its possible extragalactic origin. Our photometry of stars in the VLT images and the Gaia DR3 data allowed us to estimate the metallicity, age, color excess, and distance for Palomar 10. The Gaia DR3 data for NGC 6426 were analyzed.

We study the outer regions of the Milky Way globular cluster NGC6809 based on Dark Energy Camera (DECam) observations, which reach nearly 6 mag below the cluster main sequence (MS) turnoff. In order to unveil its fainter outermost structure, we built stellar density maps using cluster MS stars, once the contamination of field stars was removed from the cluster color-magnitude diagram. We found that only the resulting stellar density map for the lightest stars exhibits some excesses of stars at opposite sides from the cluster centre that diminish soon thereafter at ~ 0.32 deg. Studied globular clusters with apogalactic distances smaller than that of NGC6809 (5.5 kpc) do not have observed tidal tails. The lack of detection of tidal tails in the studied inner globular cluster sample could be due to the reduced diffusion time of tidal tails by the kinematically chaotic nature of the orbits of these globular clusters, thus shortening the time interval during which the tidal tails can be detected. Further investigations with an enlarged cluster sample are needed to confirm whether chaotic and non-chaotic orbits are responsible for the existence of globular clusters with tidal tails and those with extra-tidal features that are different from tidal tails or without any signatures of extended stellar density profiles., Comment: 9 pages, 4 figures. Accepted for publication in MNRAS

We detail a method to measure the correspondence between dark matter (DM) models and observations of stellar populations within Local Group dwarf spheroidal galaxies (LG dSphs) that assumes no parametric stellar distribution. Solving the spherical or cylindrical Jeans equations, we calculate the consistency of DM and stellar kinematic models with stellar positions and line-of-sight velocities. Our method can be used to search for signals of standard and exotic DM distributions. Applying our methodology to the Fornax LG dSph and using statistical bootstrapping, we find: (i) that oblate or prolate cored DM haloes match the stellar data, respectively, ≃60 or ≃370 times better than oblate or prolate cusped DM haloes for isotropic and isothermal stellar velocity dispersions, (ii) that cusped spherical DM haloes and cored spherical DM haloes match the Fornax data similarly well for isotropic stellar velocity dispersions, (iii) that the semiminor to semimajor axial ratio of spheroidal DM haloes are more extreme than 80 per cent of those predicted by Lambda cold dark matter with baryon simulations, (iv) that oblate cored or cusped DM haloes are, respectively, ≃5 or ≃30 times better matches to Fornax than prolate cored or cusped DM haloes, and (v) that Fornax shows no evidence of a disc-like structure with more than two per cent of the total DM mass. We further note that the best-fitting cusped haloes universally favour the largest mass and size fit parameters. If these extreme limits are decreased, the cusped halo likelihoods decrease relative to those of cored haloes.

Recently, two-component spherical galaxy models have been presented, where the stellar profile is described by a Jaffe law, and the total density by another Jaffe law, or by an $r^{-3}$ law at large radii. We extend these two families to their ellipsoidal axisymmetric counterparts: the JJe and J3e models. The total and stellar density distributions can have different flattenings and scale lengths, and the dark matter halo is defined by difference. First, the analytical conditions required to have a nowhere negative dark matter halo density are derived. The Jeans equations for the stellar component are then solved analytically, in the limit of small flattenings, also in presence of a central BH. The azimuthal velocity dispersion anisotropy is described by the Satoh $k$-decomposition. Finally, we present the analytical formulae for velocity fields near the center and at large radii, together with the various terms entering the Virial Theorem. The JJe and J3e models can be useful in a number of theoretical applications, e.g. to explore the role of the various parameters (flattening, relative scale lengths, mass ratios, rotational support) in determining the behavior of the stellar kinematical fields before performing more time-expensive integrations with specific galaxy models, to test codes of stellar dynamics, and in numerical simulations of gas flows in galaxies., 21 pages, 10 figures. MNRAS accepted

The vertical density distribution of stars in a galactic disc is traditionally obtained by assuming an isothermal vertical velocity dispersion of stars. Recent observations from SDSS, LAMOST, RAVE, Gaia etc show that this dispersion increases with height from the mid-plane. Here we study the dynamical effect of such non-isothermal dispersion on the self-consistent vertical density distribution for the thin disc stars in the Galaxy, obtained by solving together the Poisson equation and the equation of hydrostatic equilibrium. We find that in the non-isothermal case the mid-plane density is lower, and the scale height is higher than the corresponding values for the isothermal distribution, due to higher vertical pressure, hence the distribution is vertically more extended. The change is ~35% at the solar radius for a stars-alone disc for the typical observed linear gradient of +6.7 km $s^{-1}kpc^{-1}$ and becomes even higher with increasing radii and increasing gradients explored. The distribution shows a wing at high z, in agreement with observations, and is fitted well by a double $sech^{2}$ , which could be mis-interpreted as the existence of a second, thicker disc, specially in external galaxies. We also consider a more realistic disc consisting of gravitationally coupled stars and gas in the field of dark matter halo. The results show the same trend but the effect of non-isothermal dispersion is reduced due to the opposite, constraining effect of the gas and halo gravity. Further, the non-isothermal dispersion lowers the theoretical estimate of the total mid-plane density i.e, Oort limit value, by 16%., 12 pages, 7 figures, 2 tables, matches to the published version in MNRAS

Full author list: A Pieres, L Girardi, E Balbinot, B Santiago, L N da Costa, A Carnero Rosell, A B Pace, K Bechtol, M A T Groenewegen, A Drlica-Wagner, T S Li, M A G Maia, R L C Ogando, M dal Ponte, H T Diehl, A Amara, S Avila, E Bertin, D Brooks, D L Burke, M Carrasco Kind, J Carretero, J De Vicente, S Desai, T F Eifler, B Flaugher, P Fosalba, J Frieman, J García-Bellido, E Gaztanaga, D W Gerdes, D Gruen, R A Gruendl, J Gschwend, G Gutierrez, D L Hollowood, K Honscheid, D J James, K Kuehn, N Kuropatkin, J L Marshall, R Miquel, A A Plazas, E Sanchez, S Serrano, I Sevilla-Noarbe, E Sheldon, M Smith, M Soares-Santos, F Sobreira, E Suchyta, M E C Swanson, G Tarle, D Thomas, V Vikram, A R Walker, We present a technique to fit the stellar components of the Galaxy by comparing Hess Diagrams (HDs) generated from TRILEGAL models to real data. We apply this technique, which we call MWFITTING, to photometric data from the first 3 yr of the Dark Energy Survey (DES). After removing regions containing known resolved stellar systems such as globular clusters, dwarf galaxies, nearby galaxies, the Large Magellanic Cloud, and the Sagittarius Stream, our main sample spans a total area of ~2300 deg2. We further explore a smaller subset (~1300 deg2) that excludes all regions with known stellar streams and stellar overdensities. Validation tests on synthetic data possessing similar properties to the DES data show that the method is able to recover input parameters with a precision better than 3 per cent. We fit the DES data with an exponential thick disc model and an oblate double power-law halo model. We find that the best-fitting thick disc model has radial and vertical scale heights of 2.67 ± 0.09 kpc and 925 ± 40 pc, respectively. The stellar halo is fit with a broken power-law density profile with an oblateness of 0.75 ± 0.01, an inner index of 1.82 ± 0.08, an outer index of 4.14 ± 0.05, and a break at 18.52 ± 0.27 kpc from the Galactic centre. Several previously discovered stellar overdensities are recovered in the residual stellar density map, showing the reliability of MWFITTING in determining the Galactic components. Simulations made with the best-fitting parameters are a promising way to predict Milky Way star counts for surveys such as the LSST and Euclid., The DESDM is supported by the National Science Foundation under grants AST-1138766 and AST-1536171. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2015-71825, ESP2015-66861, FPA2015-68048, SEV-2016-0588, SEV-2016-0597, and MDM-2015-0509, some of which include ERDF funds from the European Union. IFAE is partially funded by the CERCA program of the Generalitat de Catalunya. Research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013) including ERC grant agreements 240672, 291329, and 306478. We acknowledge support from the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020, and the Brazilian Instituto Nacional de Ci?ncia e Tecnologia (INCT) do e-Universe (CNPq grant 465376/2014-2). This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Centre for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Centre for Cosmology and AstroParticle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundac¸ão Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência, Tecnologia e Inovac¸ão, the Deutsche Forschungsgemeinschaft, and the Collaborating Institutions in the DES.

Using the catalogues of galaxy clusters from The Three Hundred project, modelled with both hydrodynamic simulations, (Gadget-X and Gadget-MUSIC), and semi-analytic models (SAMs), we study the scatter and self-similarity of the profiles and distributions of the baryonic components of the clusters: the stellar and gas mass, metallicity, the stellar age, gas temperature, and the (specific) star formation rate. Through comparisons with observational results, we find that the shape and the scatter of the gas density profiles matches well the observed trends including the reduced scatter at large radii which is a signature of self-similarity suggested in previous studies. One of our simulated sets, Gadget-X, reproduces well the shape of the observed temperature profile, while Gadget-MUSIC has a higher and flatter profile in the cluster centre and a lower and steeper profile at large radii. The gas metallicity profiles from both simulation sets, despite following the observed trend, have a relatively lower normalisation. The cumulative stellar density profiles from SAMs are in better agreement with the observed result than both hydrodynamic simulations which show relatively higher profiles. The scatter in these physical profiles, especially in the cluster centre region, shows a dependence on the cluster dynamical state and on the cool-core/non-cool-core dichotomy. The stellar age, metallicity and (s)SFR show very large scatter, which are then presented in 2D maps. We also do not find any clear radial dependence of these properties. However, the brightest central galaxies have distinguishable features compared to the properties of the satellite galaxies., Comment: 20 pages, 18 figures

We use the extensive $Gaia$ Data Release 2 set of Long Period Variables to select a sample of Oxygen-rich Miras throughout the Milky Way disk and bulge for study. Exploiting the relation between Mira pulsation period and stellar age/chemistry, we slice the stellar density of the Galactic disk and bulge as a function of period. We find the morphology of both components evolves as a function of stellar age/chemistry with the stellar disk being stubby at old ages, becoming progressively thinner and more radially extended at younger stellar ages, consistent with the picture of inside-out and upside-down formation of the Milky Way's disk. We see evidence of a perturbed disk, with large-scale stellar over-densities visible both in and away from the stellar plane. We find the bulge is well modelled by a triaxial boxy distribution with an axis ratio of $\sim [1:0.4:0.3]$. The oldest of the Miras ($\sim$ 9-10 Gyr) show little bar-like morphology, whilst the younger stars appear inclined at a viewing angle of $\sim 21^{\circ}$ to the Sun-Galactic Centre line. This suggests that bar formation and buckling took place 8-9 Gyr ago, with the older Miras being hot enough to avoid being trapped by the growing bar. We find the youngest Miras to exhibit a strong peanut morphology, bearing the characteristic X-shape of an inclined bar structure., MNRAS, submitted

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio bursts. Recent observations of a Galactic FRB suggest that at least some FRBs originate from magnetars, but the origin of cosmological FRBs is still not settled. Here we report the detection of 1863 bursts in 82 hr over 54 days from the repeating source FRB~20201124A. These observations show irregular short-time variation of the Faraday rotation measure (RM), which probes the density-weighted line-of-sight magnetic field strength, of individual bursts during the first 36 days, followed by a constant RM. We detected circular polarisation in more than half of the burst sample, including one burst reaching a high fractional circular polarisation of 75%. Oscillations in fractional linear and circular polarisations as well as polarisation angle as a function of wavelength were detected. All of these features provide evidence for a complicated, dynamically evolving, magnetised immediate environment within about an astronomical unit (au; Earth-Sun distance) of the source. Our optical observations of its Milky-Way-sized, metal-rich host galaxy reveal a barred spiral, with the FRB source residing in a low stellar density, interarm region at an intermediate galactocentric distance. This environment is inconsistent with a young magnetar engine formed during an extreme explosion of a massive star that resulted in a long gamma-ray burst or superluminous supernova., Comment: 28 pages, 10 figures, updated to match the published version

Despite the impressive advances in Galactic structure studies, thanks to the large astronomical surveys, there remain several open questions. Although at low distances, optical surveys can bring us important information, the potential of NIR surveys, combined with the optical data, should be considered. In the present work, we explore the stellar distribution through the most recent NIR surveys toward low latitudes (|b| < 2° for 20° ≤ ℓ ≤ 346°) in the Galactic disk, such as 2MASS (entire plane), UKIDSS (20° ≤ ℓ ≤ 231°), and VVV-PSF data (295° ≤ ℓ ≤ 346°), avoiding directions toward the Galactic bar and bulge. Our final compilation contains nearly 140 million stars. We used this sample to perform total star counts at different longitudes, obtaining longitudinal profiles that are compared with those of other authors. For some directions, we obtained the stellar density as a function of distance to investigate the stellar distribution in the Galactic disk. As an example, the variation of the counts toward the Scutum arm tangential direction reveals the stellar content of two spiral arms, e.g., Sagittarius and Scutum. These are the preliminary results of a study that will cover a large extension of the Galactic disk.

A statistical analysis of the observed perturbations in the density of stellar streams can in principle set stringent constraints on the mass function of dark matter subhaloes, which in turn can be used to constrain the mass of the dark matter particle. However, the likelihood of a stellar density with respect to the stream and subhaloes parameters involves solving an intractable inverse problem which rests on the integration of all possible forward realizations implicitly defined by the simulation model. In order to infer the subhalo abundance, previous analyses have relied on Approximate Bayesian Computation (ABC) together with domain-motivated but handcrafted summary statistics. Here, we introduce a likelihood-free Bayesian inference pipeline based on Amortised Approximate Likelihood Ratios (AALR), which automatically learns a mapping between the data and the simulator parameters and obviates the need to handcraft a possibly insufficient summary statistic. We apply the method to the simplified case where stellar streams are only perturbed by dark matter subhaloes, thus neglecting baryonic substructures, and describe several diagnostics that demonstrate the effectiveness of the new method and the statistical quality of the learned estimator.

Numerous protoplanetary discs show distinct spiral arms features. While possibly caused by a range of processes, detailed pattern analysis points at close stellar flybys as cause for some of them. Surprisingly, these discs reside in young low-mass clusters, where close stellar flybys are expected to be rare. This fact motivated us to take a fresh look at the frequency of close flybys in low-mass clusters. In the solar neighbourhood, low-mass clusters have smaller half-mass radii than their more massive counterparts. We show that this observational fact results in the mean and central stellar density of low-mass clusters being approximately the same as in high-mass clusters, which is rarely reflected in theoretical studies. We perform N-body simulations of the stellar dynamics in young clusters obeying the observed mass-radius relation. Taking the mean disc truncation radius as a proxy for the degree of influence of the environment, we find that the influence of the environment on discs is more or less the same in low- and high-mass clusters. Even the fraction of small discs($, Comment: 18 pages, 9 figures, accepted for ApJ

The dispersal of protoplanetary disks sets the timescale available for planets to assemble, and thus it is one of the fundamental parameters in theories of planetary formation. Disk dispersal is determined by several properties of the central star, the disk itself, and the surrounding environment. In particular, the metallicity of disks may impact their evolution, even if to date controversial results exist: in low-metallicity clusters disks seem to rapidly disperse, while in the Magellanic Clouds some evidence supports the existence of accreting disks few tens of Myrs old. In this paper we study the dispersal timescale of disks in Dolidze~25, the young cluster in proximity of the Sun with lowest metallicity, with the aim of understanding whether disk evolution is impacted by the low-metallicity of the cluster. We have analyzed Chandra/ACIS-I observations of the cluster and combined the resulting source catalog with existing optical and infrared catalogs of the region. We selected the disk-bearing population and the disk-less population of Dolidze 25. We have derived stellar parameters from isochrones fitted to color-magnitude diagrams. We derived a disk fraction of about 34% and a median age of 1.2 Myrs. By comparing this estimate with existing estimates of the disk fraction of clusters younger than 10 Myrs, our study suggests that the disk fraction of Dolidze 25 is lower than what is expected from its age alone. Even if our results are not conclusive given the intrinsic uncertainty on stellar ages estimated from isochrones fitting to color-magnitude diagrams, we suggest that disk evolution in Dolidze 25 may be impacted by the environment. Given the poor O star population and low stellar density of the cluster, it is more likely that disks dispersal timescale is dictated more by the low metallicity of the cluster rather than external photoevaporation or dynamical encounters., Accepted for publication by Astronomy & Astrophysics

We have studied the kinematic properties of the candidates for hot subdwarfs (HSDs) selected by Geier et al. from the Gaia DR2 catalogue. We have used a total of 12 515 stars with relative trigonometric parallax errors less than 30\%. The HSDs are shown to have different kinematics, depending on their positions on the celestial sphere. For example, the sample of low-latitude $(|b, Comment: 18 pages, 4 figures, 4 tables

When a planet is only observed to transit once, direct measurement of its period is impossible. It is possible, however, to constrain the periods of single transiters, and this is desirable as they are likely to represent the cold and far extremes of the planet population observed by any particular survey. Improving the accuracy with which the period of single transiters can be constrained is therefore critical to enhance the long-period planet yield of surveys. Here, we combine Gaia parallaxes with stellar models and broad-band photometry to estimate the stellar densities of K2 planet host stars, then use that stellar density information to model individual planet transits and infer the posterior period distribution. We show that the densities we infer are reliable by comparing with densities derived through asteroseismology, and apply our method to 27 validation planets of known (directly measured) period, treating each transit as if it were the only one, as well as to 12 true single transiters. When we treat eccentricity as a free parameter, we achieve a fractional period uncertainty over the true single transits of $94^{+87}_{-58}\%$, and when we fix $e=0$, we achieve fractional period uncertainty $15^{+30}_{-6}\%$, a roughly threefold improvement over typical period uncertainties of previous studies., Comment: 14 pages, 11 figures. Accepted to MNRAS

Numerous studies have demonstrated the ability of Convolutional Neural Networks (CNNs) to classify large numbers of galaxies in a manner which mimics the expertise of astronomers. Such classifications are not always physically motivated, however, such as categorising galaxies by their morphological types. In this work, we consider the use of CNNs to classify simulated S0 galaxies based on fundamental physical properties. In particular, we undertake two investigations: (1) the classification of simulated S0 galaxies into three distinct evolutionary paths (isolated, tidal interaction in a group halo, and Spiral-Spiral merger), and (2) the prediction of the mass ratio for the S0s formed via mergers. To train the CNNs, we first run several hundred N-body simulations to model the formation of S0s under idealised conditions; and then we build our training datasets by creating images of stellar density and two dimensional kinematic maps for each simulated S0. Our trained networks have remarkable accuracies exceeding 99% when classifying the S0 formation pathway. For the case of predicting merger mass ratios, the mean predictions are consistent with the true values to within roughly one standard deviation across the full range of our data. Our work demonstrates the potential of CNNs to classify galaxies by the fundamental physical properties which drive their evolution., Accepted for publication in MNRAS

We explore scaling relations between the physical properties of spatially resolved regions within the galaxies that emerge in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) hydrodynamical, cosmological simulations. Using 1 kpc-scale spaxels, we compute the relationships between the star formation rate and stellar mass surface densities, i.e. the spatially resolved star-forming main sequence (rSFMS), and between the gas metallicity and the stellar mass surface density, i.e. the spatially resolved mass-metallicity relation (rMZR). We compare to observed relations derived from integral field unit surveys and imaging of galaxies. EAGLE reproduces the slope of the local ($z\approx0.1$) rSFMS well, but with a $\approx-0.15$ dex offset, close to that found for the galaxy-integrated relation. The shape of the rMZR agrees reasonably well with observations, replicating the characteristic turnover at high surface density, which we show is due to AGN feedback. The residuals of the rSFMS and rMZR are negatively (positively) correlated at low (high) surface density. The rSFMS becomes shallower as the simulation evolves from $z=2$ to 0.1, a manifestation of inside-out galaxy formation. The shape of the rMZR also exhibits dramatic evolution, from a convex profile at $z=2$ to the observed concave profile at $z=0.1$, such that the gas in regions of high stellar density is more enriched at higher redshift. The redshift independence of the relationship between the galaxy-wide gas fraction and metallicity in EAGLE galaxies is not preserved on 1 kpc scales, implying that chemical evolution is non-local due to the transport of gas and metals within galaxies., Submitted to MNRAS. 20 pages (15 + 5 appendices), 12 figures & 2 tables

Fragmentation often occurs in disk-like structures, both in the early Universe and in the context of present-day star formation. Supermassive black holes (SMBHs) are astrophysical objects whose origin is not well understood; they weigh millions of solar masses and reside in the centers of galaxies. An important formation scenario for SMBHs is based on collisions and mergers of stars in a massive cluster, in which the most massive star moves to the center of the cluster due to dynamical friction. This increases the rate of collisions and mergers since massive stars have larger collisional cross sections. This can lead to runaway growth of a very massive star which may collapse to become an intermediate-mass black hole. Here we investigate the dynamical evolution of Miyamoto-Nagai models that allow us to describe dense stellar clusters, including flattening and different degrees of rotation. We find that the collisions in these clusters depend mostly on the number of stars and the initial stellar radii for a given radial size of the cluster. By comparison, rotation seems to affect the collision rate by at most $20\%$. For flatness, we compared spherical models with systems that have a scale height of about $10\%$ of their radial extent, in this case finding a change in the collision rate of less than $25\%$. Overall, we conclude that the parameters only have a minor effect on the number of collisions. Our results also suggest that rotation helps to retain more stars in the system, reducing the number of escapers by a factor of $2-3$ depending on the model and the specific realization. After two million years, a typical lifetime of a very massive star, we find that about $630$ collisions occur in typical models with $N=10^4$, $R=100$ $\rm~R_\odot$ and a half-mass radius of $0.1$ $\rm~pc$, leading to a mass of about $6.3\times10^3$ $\rm~M_\odot$ for the most massive object., 10 pages, 7 figures

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., We present the steps taken to produce a reliable and complete input galaxy catalogue for the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey (BGS) using the photometric Legacy Survey DR8 DECam. We analyse some of the main issues faced in the selection of targets for the DESI BGS, such as star–galaxy separation, contamination by fragmented stars and bright galaxies. Our pipeline utilizes a new way to select BGS galaxies using Gaia photometry and we implement geometrical and photometric masks that reduce the number of spurious objects. The resulting catalogue is cross-matched with the Galaxy And Mass Assembly (GAMA) survey to assess the completeness of the galaxy catalogue and the performance of the target selection. We also validate the clustering of the sources in our BGS catalogue by comparing with mock catalogues and the Sloan Digital Sky Survey (SDSS) data. Finally, the robustness of the BGS selection criteria is assessed by quantifying the dependence of the target galaxy density on imaging and other properties. The largest systematic correlation we find is a 7 per cent suppression of the target density in regions of high stellar density. © 2021 The Author(s)., OR-M is supported by the Mexican National Council of Science and Technology (CONACYT) through grant no. 297228/440775 and funding from the European Union’s Horizon 2020 Framework Programme under the Marie Sklodowska-Curie grant agreement no. 734374. SC, PN, PZ, CMB, and JL acknowledge support from the Science and Technology Facilities Council through ST/P000541/1 and ST/T000244/1. ADM was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Award Number DE-SC0019022. JM gratefully acknowledges support from the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award Number DE-SC002008 and from the National Science Foundation under grant AST-1616414. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under contract no. DEAC02-05CH11231. This work also made extensive use of the NASA Astrophysics Data System and of the astro-ph preprint archive at arXiv.org. Authors want to thank the GAMA Collaboration for early access to GAMA DR4 data for this work. Some of the results in this paper have been derived using the HEALPY and HEALPIX package. We acknowledge the usage of the HyperLeda data base (http://leda.univ-lyon1.fr). The Siena Galaxy Atlas was made possible by funding support from the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award Number DE-SC002008 and from the National Science Foundation under grant AST-1616414. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work used the DiRAC@Durham facility managed by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility (www.dirac.ac.uk). The equipment was funded by BEIS capital funding via STFC capital grants ST/K00042X/1, ST/P002293/1, and ST/R002371/1, Durham University, and STFC operations grant ST/R000832/1. DiRAC is part of the National e-Infrastructure. This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under contract no. DE-AC02-05CH1123, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under contract no. AST-0950945 to the NSF’s National Optical-Infrared Astronomy Research Laboratory, the Science and Technology Facilities Council of the United Kingdom, the Gordon and Betty Moore Foundation, the Heising-Simons Foundation, the French Alternative Energies and Atomic Energy Commission (CEA), the National Council of Science and Technology, Mexico, the Ministry of Economy of Spain, and by the DESI Member Institutions. The authors are honoured to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

We model the effects of collisions and close encounters on the stellar populations observed in the Milky Way nuclear stellar cluster (NSC). Our analysis is based on $N$-body simulations in which the NSC forms by accretion of massive stellar clusters around a supermassive black hole. We attach stellar populations to our $N$-body particles and follow the evolution of their stars, and the rate of collisions and close encounters. The most common encounters are collisions between pairs of main-sequence stars, which lead to mergers: destructive collisions between main-sequence stars and compact objects are rare. We find that the effects of collisions on the stellar populations are small for three reasons. First, our models possess a core which limits the maximum stellar density. Secondly, the velocity dispersion in the NSC is similar to the surface escape velocities of the stars, which minimises the collision rate. Finally, whilst collisions between main-sequence stars destroy bright giants by accelerating their evolution, they also create them by accelerating the evolution of lower-mass stars. These two effects approximately cancel out. We also investigate whether the G2 cloud could be a fuzzball: a compact stellar core which has accreted a tenuous envelope in a close encounter with a red giant. We conclude that fuzzballs with cores below $2\,M_\odot$ have thermal times-scales too short to reproduce G2. A fuzzball with a black-hole core could reproduce the surface properties of G2 but the production rate of such objects in our model is low., 17 pages, 15 figures, 4 tables. Accepted for publication in MNRAS

New data from the $\textit{Gaia}$ satellite, when combined with accurate photometry from the Pan-STARRS survey, allow us to accurately estimate the properties of the GD-1 stream. Here, we analyze the stellar density perturbations in the GD-1 stream and show that they cannot be due to known baryonic structures like giant molecular clouds, globular clusters, or the Milky Way's bar or spiral arms. A joint analysis of the GD-1 and Pal 5 streams instead requires a population of dark substructures with masses $\approx 10^{7}$ to $10^9 \ M_{\rm{\odot}}$. We infer a total abundance of dark subhalos normalised to standard cold dark matter $n_{\rm sub}/n_{\rm sub, CDM} = 0.4 ^{+0.3}_{-0.2}$ ($68 \%$), which corresponds to a mass fraction contained in the subhalos $f_{\rm{sub}} = 0.14 ^{+0.11}_{-0.07} \%$, compatible with the predictions of hydrodynamical simulation of cold dark matter with baryons., 20 pages, 14 figures. Also see companion paper : "Novel constraints on the particle nature of dark matter from stellar streams". Accepted in MNRAS. Modified main text slightly. Updated Appendix B and added a plot. Main results and conclusions remain unchanged

The Taurus-Auriga complex is the prototypical low-mass star forming region, and provides a unique testbed of the star formation process, which left observable imprints on the spatial, kinematic, and temporal structure of its stellar population. Taurus's rich observational history has uncovered peculiarities that suggest a complicated star forming event, such as members at large distances from the molecular clouds and evidence of an age spread. With Gaia, an in-depth study of the Taurus census is possible to confirm membership, identify substructure, and reconstruct its star formation history. We have compiled an expansive census of the greater Taurus region, identifying spatial subgroups and confirming that Taurus is substructured across stellar density. There are two populations of subgroups: clustered groups near the clouds and sparse groups spread throughout the region. The sparse groups comprise Taurus's distributed population, which is on average older than the population near the clouds, and hosts sub-populations up to 15 Myr old. The ages of the clustered groups increase with distance, suggesting that the current star formation was triggered from behind. Still, the region is kinematically coherent, and its velocity structure reflects an initial turbulent spectrum similar to Larson's Law that has been modified by dynamical relaxation. Overall, Taurus has a complicated star formation history, with at least two epochs of star formation featuring both clustered and distributed modes. Given the correlations between age and spatial distribution, Taurus might be part of a galaxy-scale star forming event that can only begin to be understood in the Gaia era., Comment: Accepted to AJ, 43 pages, 14 figures, 4 tables in preprint2 format

We present the goals, strategy and first results of the high-cadence Galactic plane survey using the Zwicky Transient Facility (ZTF). The goal of the survey is to unveil the Galactic population of short-period variable stars, including short period binaries and stellar pulsators with periods less than a few hours. Between June 2018 and January 2019, we observed 64 ZTF fields resulting in 2990 deg$^2$ of high stellar density in ZTF-$r$ band along the Galactic Plane. Each field was observed continuously for 1.5 to 6 hrs with a cadence of 40 sec. Most fields have between 200 and 400 observations obtained over 2-3 continuous nights. As part of this survey we extract a total of $\approx$230 million individual objects with at least 80 epochs obtained during the high-cadence Galactic Plane survey reaching an average depth of ZTF-$r$ $\approx$20.5 mag. For four selected fields with 2 million to 10 million individual objects per field we calculate different variability statistics and find that $\approx$1-2% of the objects are astrophysically variable over the observed period. We present a progress report on recent discoveries, including a new class of compact pulsators, the first members of a new class of Roche Lobe filling hot subdwarf binaries as well as new ultracompact double white dwarfs and flaring stars. Finally we present a sample of 12 new single-mode hot subdwarf B-star pulsators with pulsation amplitudes between ZTF-$r$ = 20-76 mmag and pulsation periods between $P$ = 5.8-16 min with a strong cluster of systems with periods $\approx$ 6 min. All of the data have now been released in either ZTF Data Release 3 or data release 4., Comment: accepted for publication in MNRAS, 16 pages, 10 figures and 5 tables

In the star formation process, the vital impact of environmental factors such as feedback from massive stars and stellar density on the form of the initial mass function (IMF) at low-mass end is yet to be understood. Hence a systematic, highly sensitive observational analysis of a sample of regions under diverse environmental conditions is essential. We analyse the IMF of eight young clusters ($, Comment: Accepted for publication in Monthly Notices of Royal Astronomical Society (MNRAS). 27 pages, 24 figures, 4 tables; typos corrected

We investigate the large-scale clustering of the final spectroscopic sample of quasars from the recently completed extended Baryon Oscillation Spectroscopic Survey (eBOSS). The sample contains $343708$ objects in the redshift range $0.8, Comment: 17 pages, 13 figures, 2 tables. Accepted for publication in MNRAS. For the associated code and value-added catalogs see https://github.com/mehdirezaie/sysnetdev and https://github.com/mehdirezaie/eBOSSDR16QSOE

We present a new method for the mitigation of observational systematic effects in angular galaxy clustering via corrective random galaxy catalogues. Real and synthetic galaxy data, from the Kilo Degree Survey's (KiDS) 4$^{\rm{th}}$ Data Release (KiDS-$1000$) and the Full-sky Lognormal Astro-fields Simulation Kit (FLASK) package respectively, are used to train self-organising maps (SOMs) to learn the multivariate relationships between observed galaxy number density and up to six systematic-tracer variables, including seeing, Galactic dust extinction, and Galactic stellar density. We then create `organised' randoms, i.e. random galaxy catalogues with spatially variable number densities, mimicking the learnt systematic density modes in the data. Using realistically biased mock data, we show that these organised randoms consistently subtract spurious density modes from the two-point angular correlation function $w(\vartheta)$, correcting biases of up to $12\sigma$ in the mean clustering amplitude to as low as $0.1\sigma$, over a high signal-to-noise angular range of 7-100 arcmin. Their performance is also validated for angular clustering cross-correlations in a bright, flux-limited subset of KiDS-$1000$, comparing against an analogous sample constructed from highly-complete spectroscopic redshift data. Each organised random catalogue object is a `clone' carrying the properties of a real galaxy, and is distributed throughout the survey footprint according to the parent galaxy's position in systematics-space. Thus, sub-sample randoms are readily derived from a single master random catalogue via the same selection as applied to the real galaxies. Our method is expected to improve in performance with increased survey area, galaxy number density, and systematic contamination, making organised randoms extremely promising for current and future clustering analyses of faint samples., Comment: 19 pages (7 appendix pages), 12 figures (8 appendix figures), accepted to A&A

The flat stellar density cores of massive elliptical galaxies form rapidly due to sinking supermassive black holes (SMBHs) in gas-poor galaxy mergers. After the SMBHs form a bound binary, gravitational slingshot interactions with nearby stars drive the core regions towards a tangentially biased stellar velocity distribution. We use collisionless galaxy merger simulations with accurate collisional orbit integration around the central SMBHs to demonstrate that the removal of stars from the centre by slingshot kicks accounts for the entire change in velocity anisotropy. The rate of strong (unbinding) kicks is constant over several hundred Myr at $\sim 3 \ \mathrm{ M}_\odot\, \rm yr^{-1}$ for our most massive SMBH binary (MBH = 1.7 × 1010 M⊙). Using a frequency-based orbit classification scheme (box, x-tube, z-tube, rosette), we demonstrate that slingshot kicks mostly affect box orbits with small pericentre distances, leading to a velocity anisotropy of β ≲ −0.6 within several hundred Myr as observed in massive ellipticals with large cores. We show how different SMBH masses affect the orbital structure of the merger remnants and present a kinematic tomography connecting orbit families to integral field kinematic features. Our direct orbit classification agrees remarkably well with a modern triaxial Schwarzschild analysis applied to simulated mock kinematic maps.

We study the outer regions of the Milky Way globular cluster NGC6981 from publicly available $BV$ photometry and new Dark Energy Camera (DECam) observations, both reaching nearly 4 mag below the cluster main sequence (MS) turnoff. While the $BV$ data sets reveal the present of extra-tidal features around the cluster, the much larger field of view of DECam observations allowed us to identify some other tidal features, which extend from the cluster toward the opposite direction to the Milky Way center. These cluster structural features arise from stellar density maps built using MS stars, once the cluster color-magnitude diagram was cleaned from the contamination of field stars. We also performed $N$-body simulations in order to help us to understand the spatial distribution of the extra-tidal debris. The outcomes reveal the presenceof long trailing and leading tails mostly parallel to the direction of the cluster velocity vector. We found that the cluster has lost most of its mass by tidal disruption during its perigalactic passages, that lasted nearly 20 Myr each. Hence, a decrease in the density of escaping stars near the cluster is expected from our $N$-body simulations, which in turn means that stronger extra-tidal features could be found out by exploring much larger areas around NGC6891., Comment: 8 pages, 10 figures. Accepted for publication in Astronomy & Astrophysics

The first stages of planet formation usually occur when the host star is still in a (relatively) dense star-forming region, where the effects of the external environment may be important for understanding the outcome of the planet formation process. In particular, star-forming regions that contain massive stars have strong far ultraviolet (FUV) and extreme ultraviolet (EUV) radiation fields, which can induce mass-loss from protoplanetary discs due to photoevaporation. In this paper we present a parameter-space study of the expected FUV and EUV fields in N-body simulations of star-forming regions with a range of initial conditions. We then use recently published models to determine the mass-loss due to photoevaporation from protoplanetary discs. In particular, we focus on the effects of changing the initial degree of spatial structure and initial virial ratio in the star-forming regions, as well as the initial stellar density. We find that the FUV fields in star-forming regions are much higher than in the interstellar medium, even when the regions have stellar densities as low as in the Galactic field, due to the presence of intermediate-mass, and massive, stars (>5Msun). These strong radiation fields lead to the destruction of the gas component in protoplanetary discs within 1 Myr, implying that gas giant planets must either form extremely rapidly (, 18 pages (including two short appendices), 6 Fgiures in main paper, accepted for publication in MNRAS

Circumstellar discs are the precursors of planetary systems and develop shortly after their host star has formed. In their early stages these discs are immersed in an environment rich in gas and neighbouring stars, which can be hostile for their survival. There are several environmental processes that affect the evolution of circumstellar discs, and external photoevaporation is arguably one of the most important ones. Theoretical and observational evidence point to circumstellar discs losing mass quickly when in the vicinity of massive, bright stars. In this work we simulate circumstellar discs in clustered environments in a range of stellar densities, where the photoevaporation mass-loss process is resolved simultaneously with the stellar dynamics, stellar evolution, and the viscous evolution of the discs. Our results indicate that external photoevaporation is efficient in depleting disc masses and that the degree of its effect is related to stellar density. We find that a local stellar density lower than 100 stars pc$^{-2}$ is necessary for discs massive enough to form planets to survive for \SI{2.0}{Myr}. There is an order of magnitude difference in the disc masses in regions of projected density 100 stars pc$^{-2}$ versus $10^4$ stars pc$^{-2}$. We compare our results to observations of the Lupus clouds, the Orion Nebula Cluster, the Orion Molecular Cloud-2, Taurus, and NGC 2024, and find that the trends observed between region density and disc masses are similar to those in our simulations., Accepted for publication in MNRAS. 9 pages, 4 figures

Using the TNG100 (100 Mpc)^3 simulation of the IllustrisTNG project, we demonstrate a strong connection between the onset of star formation quenching and the stellar size of galaxies. We do so by tracking the evolutionary history of extended and normal-size galaxies selected at z=2 with log(M_star) = 10.2 - 11 and stellar-half-mass-radii above and within 1-sigma of the stellar size--stellar mass relation, respectively. We match the stellar mass and star formation rate distributions of the two populations. By z=1, only 36% of the extended massive galaxies have quenched, in contrast to a quenched fraction of 69% for the normal-size massive galaxies. We find that normal-size massive galaxies build up their central stellar mass without a significant increase in their stellar size between z=2-4, whereas the stellar size of the extended massive galaxies almost doubles in the same time. In IllustrisTNG, lower black hole masses and weaker kinetic-mode feedback appears to be responsible for the delayed quenching of star formation in the extended massive galaxies. We show that relatively gas-poor mergers may be responsible for the lower central stellar density and weaker supermassive black hole feedback in the extended massive galaxies., 15 pages, 9 figures, Accepted for publication in the Astrophysical Journal

Energetic feedback from star clusters plays a pivotal role in shaping the dynamical evolution of giant molecular clouds (GMCs). To study the effects of stellar feedback on the star formation efficiency of the clouds and the dynamical response of embedded star clusters, we perform a suite of isolated GMC simulations with star formation and momentum feedback subgrid models using the moving-mesh hydrodynamics code \textsc{Arepo}. The properties of our simulated GMCs span a wide range of initial mass, radius, and velocity configurations. We find that the ratio of the final stellar mass to the total cloud mass, $\epsilon_{\rm int}$, scales strongly with the initial cloud surface density and momentum feedback strength. This correlation is explained by an analytic model that considers force balancing between gravity and momentum feedback. For all simulated GMCs, the stellar density profiles are systematically steeper than that of the gas at the epochs of the peaks of star formation, suggesting a centrally concentrated stellar distribution. We also find that star clusters are always in a sub-virial state with a virial parameter $\sim0.6$ prior to gas expulsion. Both the sub-virial dynamical state and steeper stellar density profiles prevent clusters from dispersal during the gas removal phase of their evolution. The final cluster bound fraction is a continuously increasing function of $\epsilon_{\rm int}$. GMCs with star formation efficiency smaller than 0.5 are still able to form clusters with large bound fractions., Comment: 17 pages, 13 figures; Match the published version in MNRAS

27 pags., 19 figs., 4 tabs., Molecular hydrogen being unobservable in cold molecular clouds, the column density measurements of molecular gas currently rely either on dust emission observation in the far-IR or on star counting. (Sub-)millimeter observations of numerous trace molecules are effective from ground based telescopes, but the relationships between the emission of one molecular line and the H2 column density (NH2) is non-linear and sensitive to excitation conditions, optical depths, abundance variations due to the underlying physico-chemistry. We aim to use multi-molecule line emission to infer NH2 from radio observations. We propose a data-driven approach to determine NH2 from radio molecular line observations. We use supervised machine learning methods (Random Forests) on wide-field hyperspectral IRAM-30m observations of the Orion B molecular cloud to train a predictor of NH2, using a limited set of molecular lines as input, and the Herschel-based dust-derived NH2 as ground truth output. For conditions similar to the Orion B molecular cloud, we obtain predictions of NH2 within a typical factor of 1.2 from the Herschel-based estimates. An analysis of the contributions of the different lines to the predictions show that the most important lines are $^{13}$CO(1-0), $^{12}$CO(1-0), C$^{18}$O(1-0), and HCO$^+$(1-0). A detailed analysis distinguishing between diffuse, translucent, filamentary, and dense core conditions show that the importance of these four lines depends on the regime, and that it is recommended to add the N$_2$H$^+$(1-0) and CH$_3$OH(20-10) lines for the prediction of NH2 in dense core conditions. This article opens a promising avenue to directly infer important physical parameters from the molecular line emission in the millimeter domain. The next step will be to try to infer several parameters simultaneously (e.g., NH2 and far-UV illumination field) to further test the method. [Abridged], This work is based on observations carried out under project numbers 019-13, 022-14, 145-14, 122-15, 018-16, and finally the large program number 124-16 with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). This research also used data from the Herschel Gould Belt survey (HGBS) project (http:// gouldbelt-herschel.cea.fr). The HGBS is a Herschel Key Programme jointly carried out by SPIRE Specialist Astronomy Group 3 (SAG 3), scientists of several institutes in the PACS Consortium (CEA Saclay, INAF-IFSI Rome and INAF-Arcetri, KU Leuven, MPIA Heidelberg), and scientists of the Herschel Science Center (HSC). We thank CIAS for their hospitality during the many workshops devoted to the ORION-B project. This work was supported in part by the Programme National “Physique et Chimie du Milieu Interstellaire” (PCMI) of CNRS/INSU with INC/INP, co-funded by CEA and CNES. This project has received financial support from the CNRS through the MITI interdisciplinary programs. J.R.G. thanks Spanish MICI for funding support under grant AYA2017-85111-P.

While magnetic fields have long been considered to be important for the evolution of magnetic non-degenerate stars and compact stars, it has become clear in recent years that actually all of the stars are deeply affected. This is particularly true regarding their internal angular momentum distribution, but magnetic fields may also influence internal mixing processes and even the fate of the star. We propose a new framework for stellar evolution simulations, in which the interplay between magnetic field, rotation, mass loss, and changes in the stellar density and temperature distributions are treated self-consistently. For average large-scale stellar magnetic fields which are symmetric to the axis of rotation of the star, we derive 1D evolution equations for the toroidal and poloidal components from the mean-field MHD equation by applying Alfven's theorem, and a conservative form of the angular momentum transfer due to the Lorentz force is formulated. We implement our formalism into a numerical stellar evolution code and simulate the magneto-rotational evolution of 1.5 M$_\odot$ stars. The Lorentz force aided by the $\Omega$ effect imposes torsional Alfven waves propagating through the magnetized medium, leading to near-rigid rotation within the Alfven timescale. Our models with different initial spins and B-fields can reproduce the main observed properties of Ap/Bp stars. Calculations continued to the red-giant regime show a pronounced core-envelope coupling, which reproduces the core and surface rotation periods determined by asteroseismic observations., Comment: Accepted for publication in A&A. 29 pages, 13+figures, 1 Table

The dynamical formation of black hole binaries in globular clusters that merge due to gravitational waves occurs more frequently in higher stellar density. Meanwhile, the probability to form intermediate mass black holes (IMBHs) also increases with the density. To explore the impact of the formation and growth of IMBHs on the population of stellar mass black hole binaries from globular clusters, we analyze the existing large survey of Monte-Carlo globular cluster simulation data (MOCCA SURVEY Database I). We show that the number of binary black hole mergers agrees with the prediction based on clusters' initial properties when the IMBH mass is not massive enough or the IMBH seed forms at a later time. However, binary black hole formation and subsequent merger events are significantly reduced compared to the prediction when the present-day IMBH mass is more massive than $\sim10^4 \rm M_{\odot}$ or the present-day IMBH mass exceeds about 1 per cent of cluster's initial total mass. By examining the maximum black hole mass in the system at the moment of black hole binary escaping, we find that $\sim$ 90 per cent of the merging binary black holes escape before the formation and growth of the IMBH. Furthermore, large fraction of stellar mass black holes are merged into the IMBH or escape as single black holes from globular clusters in cases of massive IMBHs, which can lead to the significant under-population of binary black holes merging with gravitational waves by a factor of 2 depending on the clusters' initial distributions., 9 pages, 8 figures, Accepted for publication in MNRAS

NGC 300 is a low-mass disk galaxy in the Sculptor group. In the literature, it has been identified as a pure exponential disk galaxy, as its luminosity profile could be well fitted with a single exponential law over many disk scale lengths (Type I). We investigate the stellar luminosity distribution of NGC 300 using $Hubble$ $Space$ $Telescope$ (HST) archive data, reaching farther and deeper than any other previous studies. Color magnitude diagrams show a significant population of old red giant branch (RGB) stars in all fields out to $R\sim19$ kpc ($32'$), as well as younger populations in the inner regions. We construct the density profiles of the young, intermediate-aged, and old stellar populations. We find two clear breaks in the density profiles of the old RGB and intermediate-aged stars: one down-bending (Type II) at $R\sim5.9$ kpc, and another up-bending (Type III) at $R\sim8.3$ kpc. Moreover, the old RGB stars exhibit a negative radial color gradient with an up-bending at $R\sim8$~kpc, beyond which the stellar populations are uniformly old ($>$7~Gyr) and metal-poor ($\rm[Fe/H] = -1.6^{+0.2}_{-0.4}$ dex). The outer stellar component at $R\gtrapprox8$ kpc is, therefore, well separated from the inner disk in terms of the stellar density and stellar populations. While our results cast doubt on the currently established wisdom that NGC\,300 is a pure exponential disk galaxy, a more detailed survey should be carried out to identify the outskirts as either a disk or a stellar halo., 6 pages, 5 figures, 1 appendix, accepted for publication in A&A Letters

Observationally, it has been reported that the densest stellar system in the Universe does not exceed a maximum stellar surface density, $\Sigma^{\max}_{*}$ = $3\times10^5$M$_{\odot}$pc$^{-2}$, throughout a wide physical scale ranging from star cluster to galaxy. This suggests there exists a fundamental physics which regulates the star formation and stellar density. However, factors that determine this maximum limit are not clear. In this study, we show that $\Sigma^{\max}_{*}$ of galaxies is not a constant as previous work reported, but actually depends on the stellar mass. We select galaxy sample from the Sloan Digital Sky Survey Data Release 12 at $z=0.01-0.5$. In contrast to a constant maximum predicted by theoretical models, $\Sigma^{\max}_{*}$ strongly depends on stellar mass especially for less massive galaxies with $\sim10^{10}$M$_{\odot}$. We also found that a majority of high-$\Sigma_{*}$ galaxies show red colours and low star-formation rates. These galaxies probably reach the $\Sigma^{\max}_{*}$ as a consequence of the galaxy evolution from blue star forming to red quiescent by quenching star formation. One possible explanation of the stellar-mass dependency of $\Sigma^{\max}_{*}$ is a mass dependent efficiency of stellar feedback. The stellar feedback could be relatively more efficient in a shallower gravitational potential, which terminates star formation quickly before the stellar system reaches a high stellar density., Comment: 6 pages, 6 figures, accepted for publication in MNRAS. Summary of the paper can be found at https://www.youtube.com/watch?v=7OVnOmT25O0

Aims. In this work we aim to estimate the lowest stellar mass that MICADO at the ELT will be able to reliably detect given a stellar density and distance. We also show that instrumental effects that will play a critical role, and report the number of young clusters that will be accessible for IMF studies in the local Universe with the ELT. Methods. We used SimCADO, the instrument simulator package for the MICADO camera, to generate observations of 56 dense stellar regions with densities similar to the cores of young stellar clusters. We placed the cluster fields at distances between 8 kpc and 5 Mpc from the Earth, implying core densities from 10^2 to 10^5 stars arcsec^-2, and determined the lowest reliably observable mass for each stellar field through point-spread function (PSF) fitting photometry. Results. Our results show that stellar densities of 2 Msun will be resolved in fields of, Comment: 13 pages, 8 figures, 3 tables

We report on the search for overall kinematical or structural conditions that have allowed some Milky Way globular clusters to presently develop tidal tails. For this purpose, we build a comprehensive catalogue of globular clusters with studies focused on their outermost regions and classified them in three categories: those with observed tidal tails, those with extra-tidal features different from tidal tails and those without any signature of extended stellar density profiles. When exploring different kinematical and structural parameter spaces, we found that globular clusters - irrespective from the presence of tidal tails, or any other kind of extra-tidal features or the absence of them - behave similarly. In general, globular clusters whose orbits are relatively more eccentric and very inclined respect to the Milky Way plane have undergone a larger amount of mass-loss by tidal disruption. The latter has also accelerated the internal dynamics toward a comparatively more advanced stage of evolution. These outcomes show that it is not straightforward to find any particular set of parameter space and dynamical conditions that can definitely predict tidal tails along globular clusters in the Milky Way., Comment: 5 pages, 3 figures. Accepted for publication in Astronomy & Astrophysics Letters

This work is based on deep multi-band (g, r, i) data from the Fornax Deep Survey with VST. We analyse the surface brightness profiles of the 19 bright ETGs inside the virial radius of the Fornax cluster. The main aim of this work is to identify signatures of accretion onto galaxies by studying the presence of outer stellar halos, and understand their nature and occurrence. Our analysis also provides a new and accurate estimate of the intra-cluster light inside the virial radius of Fornax. We performed multi-component fits to the azimuthally averaged surface brightness profiles available for all sample galaxies. This allows to quantify the relative weight of all components in the galaxy structure that contribute to the total light. In addition, we derived the average g-i colours in each component identified by the fit, as well as the azimuthally averaged g-i colour profiles, to correlate them with the stellar mass of each galaxy and the location inside the cluster. We find that in the most massive and reddest ETGs the fraction of light in, probably accreted, halos is much larger than in the other galaxies. Less-massive galaxies have an accreted mass fraction lower than 30%, bluer colours and reside in the low-density regions of the cluster. Inside the virial radius of the cluster, the total luminosity of the intra-cluster light, compared with the total luminosity of all cluster members, is about 34%. Inside the Fornax cluster there is a clear correlation between the amount of accreted material in the stellar halos of galaxies and the density of the environment in which those galaxies reside. By comparing this quantity with theoretical predictions and previous observational estimates, there is a clear indication that the driving factor for the accretion process is the total stellar mass of the galaxy, in agreement with the hierarchical accretion scenario., 18 pages, 10 figures. Accepted for publication in A&A

AIMS. We calculate the stellar density using star counts obtained from Gaia DR2 up to a Galactocentric distance R=20 kpc with a deconvolution technique for the parallax errors. Then we analyse the density in order to study the structure of the outer Galactic disc, mainly the warp. METHODS. In order to carry out the deconvolution, we used the Lucy inversion technique for recovering the corrected star counts. We also used the Gaia luminosity function of stars with $M_G, Comment: 19 pages, 21 figures, accepted to be published in A&A

The aim of this paper is to test the need for non-baryonic dark matter in the context of galactic rotation and the apparent difference between distributions of galactic mass and luminosity. We present a set of rotation curves and 3.6 &mu, m surface brightness profiles for a diverse sample of 214 galaxies. Using rotation curves as the sole input into our Newtonian disk model, we compute non-parametric radial profiles of surface mass density. All profiles exhibit lower density than parametric models with dark halos and provide a superior fit with observed rotation curves. Assuming all dynamical mass is in main-sequence stars, we estimate radial distributions of characteristic star mass implied by the corresponding pairs of density and brightness profiles. We find that for 132 galaxies or 62% of the sample, the relation between density and brightness can be fully explained by a radially declining stellar mass gradient. Such idealized stellar population fitting can also largely address density and brightness distributions of the remaining 82 galaxies, but their periphery shows, on average, 14 M⊙/pc2 difference between total density and light-constrained stellar density. We discuss how this density gap can be interpreted, by considering a low-luminosity baryonic matter, observational uncertainties, and visibility cutoffs for red dwarf populations. Lastly, we report tight correlation between radial density and brightness trends, and the discovered flattening of surface brightness profiles&mdash, both being evidence against dark matter. Our findings make non-baryonic dark matter unnecessary in the context of galactic rotation.

We compute the tidal disruption event (TDE) rate around local massive black holes (MBHs) with masses as low as $2.5\times10^4 {\rm M}_\odot$, thus probing the dwarf regime for the first time. We select a sample of 37 galaxies for which we have the surface stellar density profile, a dynamical estimate of the mass of the MBH, and 6 of which, including our Milky Way, have a resolved nuclear star cluster (NSC). For the Milky Way, we find a total TDE rate of $\sim 10^{-4}{\rm yr}^{-1}$ when taking the NSC in account, and $\sim 10^{-7} {\rm yr}^{-1}$ otherwise. TDEs are mainly sourced from the NSC for light ($, Accepted in MNRAS

We present results on the basis of Dark Energy Camera Legacy Survey (DECaLS) DR8 astrometric and photometric data sets of the Milky Way globular cluster Pal 13. Because of its relative small size and mass, there has not been yet a general consensus about the existence of extra-tidal structures around it. While some previous results claim for the absence of such features, others have shown that the cluster is under the effects of tidal stripping. From DECaLS g,r magnitudes of stars placed along the cluster Main Sequence in the colour-magnitude diagram --previously corrected by interstellar reddening--, we built the cluster stellar density map. The resulting density map shows nearly smooth contours around Pal 13 out to 1.6 times the most recent estimate of its Jacobi radius, derived by taking into account its variation along its orbital motion. This outcome favours the presence of stars escaping the cluster, a phenomenon frequently seen in globular clusters that have crossed the Milky Way disc a comparable large number of times. Particularly, the orbital high eccentricity and large inclination angle of this accreted globular cluster could have been responsible for the relatively large amount of cluster mass lost., Comment: 8 pages, 6 figures. Accepted for publication in Astronomy & Astrophysics

We evaluate the impact of imaging systematics on the clustering of luminous red galaxies (LRG), emission-line galaxies (ELG), and quasars (QSO) targeted for the upcoming Dark Energy Spectroscopic Instrument (DESI) survey. Using Data Release 7 of the DECam Legacy Survey, we study the effects of astrophysical foregrounds, stellar contamination, differences between north galactic cap and south galactic cap measurements, and variations in imaging depth, stellar density, galactic extinction, seeing, airmass, sky brightness, and exposure time before presenting survey masks and weights to mitigate these effects. With our sanitized samples in hand, we conduct a preliminary analysis of the clustering amplitude and evolution of the DESI main targets. From measurements of the angular correlation functions, we determine power law fits r(0) = 7.78 +/- 0.26 h(-1) Mpc, gamma = 1.98 +/- 0.02 for LRGs and r(0) = 5.45 +/- 0.1 h(-1) Mpc, gamma = 1.54 +/- 0.01 for ELGs. Additionally, from the angular power spectra, we measure the linear biases and model the scale-dependent biases in the weakly non-linear regime. Both sets of clustering measurements show good agreement with survey requirements for LRGs and ELGs, attesting that these samples will enable DESI to achieve precise cosmological constraints. We also present clustering as a function of magnitude, use cross-correlations with external spectroscopy to infer dN/dz and measure clustering as a function of luminosity, and probe higher order clustering statistics through counts-in-cells moments.© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society, The authors thank Stephen Bailey, Daniel Eisenstein, Shirley Ho, Dustin Lang, Jeffrey Newman, Anand Raichoor, Ashley Ross, HeeJong Seo, Mike Wilson, Christophe Y`eche, and Pauline Zarrouk for many useful discussions. E. K. and M. W. are supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award No. DE-SC0017860. D. S., J. G., M. L., and J. M. are supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under contract no. DE-AC02-05CH11231, and by the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility under the same contract. This work also made extensive use of the NASA Astrophysics Data System and of the astro-ph preprint archive at arXiv.org. Additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under contract no. AST-0950945 to the National Optical Astronomy Observatory; the Science and Technologies Facilities Council of theUnitedKingdom; theGordon and Betty Moore Foundation; the Heising-Simons Foundation; the National Council of Science and Technology of Mexico; and by the DESI Member Institutions. The authors are honored to be permitted to conduct astronomical research on Iolkam Duag (Kitt Peak), a mountain with particular significance to the Tohono O'odham Nation.