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We present a novel code, named SIESTA (Statistical matchIng between rEal and Synthetic sTellar popuLations), designed for performing statistical isochrone fitting to colour–magnitude diagrams (CMDs) of single stellar populations by leveraging comparisons between the observed stellar distribution and predictions from synthetic populations, simulated on top of a grid of isochrones. These synthetic populations encompass determinant factors such as the cluster's initial mass function (IMF), the presence of non-resolved binaries, as well as the expected photometric errors, and observational completeness (or the observed luminosity function). Employing Markov Chain Monte Carlo within a Bayesian framework, SIESTA allows for the determination of a cluster's age, metallicity, distance, colour excess, and binary fraction (with masses exceeding a certain ratio). In this study, we rigorously benchmark the SIESTA code utilizing synthetic populations and evaluate its performance against observations from the VISCACHA Survey in the Small Magellanic Cloud, focusing on five star clusters: Lindsay 114, NGC 152, Lindsay 91, Lindsay 113, and NGC 121. These clusters were chosen for their diverse age range, spanning from 0.04 to 10 Gyr. Our findings demonstrate the capability of the SIESTA code to accurately represent the observed CMDs of these clusters. Furthermore, we compare the results obtained with SIESTA to previous characterizations of these clusters, highlighting the consistency between the derived metallicity and spectroscopic determinations from various sources. [ABSTRACT FROM AUTHOR]

Gravitational lensing may render individual high-mass stars detectable out to cosmological distances, and several extremely magnified stars have in recent years been detected out to redshifts |$z\approx 6$|⁠. Here, we present Muspelheim, a model for the evolving spectral energy distributions of both metal-enriched and metal-free stars at high redshifts. Using this model, we argue that lensed stars will form a highly biased sample of the intrinsic distribution of stars across the Hertzsprung–Russell diagram, and that this bias will typically tend to favour the detection of lensed stars in evolved stages characterized by low effective temperatures, even though stars only spend a minor fraction of their lifetimes in such states. We also explore the prospects of detecting individual, lensed metal-free (Population III) stars at high redshifts using the James Webb Space Telescope (JWST). We find that very massive (⁠|$\gtrsim 100\ \mathrm{M}_\odot$|⁠) Population III stars at |$z\gtrsim 6$| may potentially be detected by JWST in surveys covering large numbers of strong-lensing clusters, provided that the Population III stellar initial mass function is sufficiently top-heavy, that these stars evolve to effective temperatures |$\le 15000$| K, and that the cosmic star formation rate density of Pop III stars reaches |$\gtrsim 10^{-4}\ \mathrm{M}_\odot$| cMpc |$^{-3}$| yr |$^{-1}$| at |$z\approx 6$| –10. Various ways to distinguish metal-free lensed stars from metal-enriched ones are also discussed. [ABSTRACT FROM AUTHOR]

The question of whether the Milky Way's disc extends to low metallicity has been the subject of debate for many years. We aim to address the question by employing a large sample of giant stars with radial velocities and homogeneous metallicities based on the Gaia Data Release 3 BP/RP(XP) spectra. We study the 3D velocity distribution of stars in various metallicity ranges, including the very metal-poor (VMP) regime (⁠|$\mathrm{[M/H]} < -2.0$|⁠). We find that a clear, stand-alone disc population, i.e. that with a ratio of rotational velocity to velocity dispersion |$v/\sigma > 1$|⁠ , starts to emerge only around |$\mathrm{[M/H]} \sim -1.3$|⁠ , and is not visible for |$\mathrm{[M/H]} < -1.6$|⁠. Using Gaussian mixture modelling, we show that there are two halo populations in the VMP regime: one stationary and one with a net prograde rotation of |$\sim\!\! 80\ \mathrm{km\, s}^{-1}$|⁠. In this low-metallicity range, we are able to place constraints on the contribution of a rotation-supported thick disc sub-population to a maximum of |$\sim\!\! 3$| per cent in our sample. We compare our results to previous claims of discy VMP stars in both observations and simulations and find that having a prograde halo component could explain most of these. [ABSTRACT FROM AUTHOR]

In recent years, the study of the Milky Way has significantly advanced due to extensive spectroscopic surveys of its stars, complemented by astroseismic and astrometric data. However, it remains disjoint from recent advancements in understanding the physics of the Galactic interstellar medium (ISM). This paper introduces a new model for the chemical evolution of the Milky Way that can be constrained on stellar data, because it combines a state-of-the-art ISM model with a Milky Way stellar disc model. Utilizing a data set of red clump stars from APOGEE, known for their precise ages and metallicities, we concentrate on the last 6 billion years – a period marked by Milky Way's secular evolution. We examine the oxygen abundance in the low- |$\alpha$| disc stars relative to their ages and birth radii, validating or constraining critical ISM parameters that remain largely unexplored in extragalactic observations. The models that successfully reproduce the radius–metallicity distribution and the age–metallicity distribution of stars without violating existing ISM observations indicate a need for modest differential oxygen enrichment in Galactic outflows, meaning that the oxygen abundance of outflows is higher than the local ISM abundance, irrespective of outflow mass loading. The models also suggest somewhat elevated ISM gas velocity dispersion levels over the past 6 billion years compared to galaxies of similar mass. The extra turbulence necessary could result from energy from gas accretion onto the Galaxy, supernovae clustering in the ISM, or increased star formation efficiency per freefall time. This work provides a novel approach to constraining the Galactic ISM and outflows, leveraging the detailed insights available from contemporary Milky Way surveys. [ABSTRACT FROM AUTHOR]

Context. The dynamical evolution of open clusters is driven by stellar evolution, internal dynamics, and external forces, which according to dynamical simulations will lead to their evaporation over a timescale of about 1 Ga. However, about 10% of the known open clusters are older. These latter are special systems whose detailed properties are related to their dynamical evolution and the balance between mechanisms of cluster formation and dissolution. Aims. We investigated the spatial distribution and structural parameters of six open clusters older than 1 Ga in order to constrain their dynamical evolution and longevity. Methods. We identified members using Gaia EDR3 data up to a distance of 150 pc from the centre of each cluster. We investigated the spatial distribution of stars inside each cluster to understand their degree of mass segregation. Finally, in order to interpret the obtained radial density profiles, we reproduced them using the lowered isothermal model explorer with PYthon (LIMEPY) and the spherical potential escapers stitched (SPES) models. Results. All the studied clusters appear to be more extended than previously reported in the literature. The spatial distributions of three of them show some structures aligned with their orbits. These structures may be related to the existence of extra tidal stars. Moreover, we find that about 20% of their members have sufficient energy to leave the systems or are already unbound. Together with their initial masses, their distances to the Galactic plane may play significant roles in their survival. We find clear evidence that the most dynamically evolved clusters do not fill their Roche volumes, appearing more concentrated than the others. Finally, we find a cusp–core dichotomy in the central regions of the studied clusters, which shows some similarities to that observed among globular clusters. [ABSTRACT FROM AUTHOR]

We present results from a recent study of the spin rate properties of a sample of more than 400 Galactic O-type stars surveyed by the IACOB and OWN projects. We combine vsini, Teff, and logg estimates with information about the spectroscopic binarity status for 285 of the stars in the sample, and provide a renewed overview about how the empirical distribution of projected rotational velocities in the O-star domain depends on mass, evolutionary and binary status. The obtained distributions are then compared with predictions of state-of-the-art population synthesis simulations including binary interaction, and used to provide hints about the initial velocity distribution of stars with masses in the range 15-80 M⊙. [ABSTRACT FROM AUTHOR]

If primordial black holes (PBHs) constitute the dark matter (DM), stars forming in dark-matter dominated environments with low velocity dispersions, such as ultra-faint dwarf galaxies, may capture a black hole at birth. The capture probability is non-negligible for PBHs of masses around 1020 g, and increases with stellar mass. Moreover, infected stars are turned into virtually invisible black holes on cosmologically short time-scales. Hence, the number of observed massive main-sequence stars in ultra-faint dwarfs should be suppressed if the DM was made of asteroid-mass PBHs. This would impact the measured mass distribution of stars, making it top-light (i.e. depleted in the high-mass range). Using simulated data that mimic the present-day observational power of telescopes, we show that already existing measurements of the mass function of stars in local ultra-faint dwarfs could be used to constrain the fraction of DM composed of PBHs in the – currently unconstrained – mass range of 1019–1021 g. [ABSTRACT FROM AUTHOR]

Antonie ('Anton') Pannekoek (1873 -1960), the founder of the Astronomical Institute of the University of Amsterdam, is remembered as one of the initiators of the field of stellar atmospheres. A second, maybe equally significant part of his research and legacy did not concern stellar, but Galactic astronomy. He was awarded an honorary doctorate by Harvard University and the Gold Medal of the Royal Astronomical Society (UK) for his total research effort. From his long-term interest in viewing and mapping the Milky Way he became convinced that the sidereal system was built up of clouds of stars, condensations of various sizes in a smooth but low-density stratum of stars. In addition, there were dark clouds together with streaks with little or no extinction in between them. So, he took the opposite view of Jacobus C. Kapteyn, concerning the stellar distribution, which the latter regarded in first approximation to be smooth and uniform in longitude so that star counts as a function of apparent magnitude depended primarily on latitude. Pannekoek's research into the structure of the stellar system consisted of various parts. He first looked at bright clouds of the Milky Way, such as in Cygnus, and assuming these were isolated structures he estimated their distance from their contribution to star counts by stars far out in the bright tail of the luminosity function. He found values of tens of kpc, which would mean their distribution was similar in extent to that of Shapley's globular cluster system. Later he had to reduce his distance by a factor over two, and later still to admit he had to retract the method altogether. He developed a rigorous method of estimating distances of dark clouds from modeling star counts off and on the cloud, preceding Wolf's quick and crude method that became very widely applied. He should have received more credit for this. During the 1920s it became clear that extinction was a major effect and that the Galaxy rotated around a distant center. Pannekoek unsuccessfully looked for the large central mass, that Oort found had to be in the center of rotation in the Galaxy, by estimating masses of some bright star clouds in the Milky Way. He also pioneered the mapping of the local structure in the Galaxy from spectroscopic parallaxes, using the fact--following Kapteyn's study of 'helium stars'--that for B- and A-stars and K-giants the intrinsic dispersion in absolute magnitude is small. The distributions of different spectral types are substantially different. He tried without success to explain Kapteyn's Star Streams from the gravitational pull of the irregular distribution of matter in the solar neighborhood. As a teenager he was fascinated by the appearance of the Milky Way and he started producing sketches of the Milky Way by drawing curves of equal (surface) brightness or in modern terms isophotes. In the course of his career this resulted in isophotal maps of both the northern and the southern Milky Way, first from visual observations, later from photographic surface photometry using out-of-focus exposures. The care and patience with which he visually produced his maps is admirable. For the photographic work he enlisted help from Wolf in Heidelberg and Vote at Lembang, who both provided extensive plate material. Unlike the care that has been employed for photographic surface photometry in more recent times, a wide range of photographic emulsions and developers was used and calibration of the characteristic curve was done on separate plates "... of the same type, if possible!" (my italics). In this paper I compare Pannekoek's resulting isophotal maps with detailed photographic surface photometry of the southern Milky Way in the 1980s and 1990s by the group in Bochum and to the almost all-sky mapping by the Pioneer 10 spacecraft, free of zodiacal light, from beyond the asteroid belt. This shows Pannekoek's visual and photographic maps to be surprisingly accurate, in spite of all the non-uniformity in observers for the first category and in exposure, emulsion, etc., with magnitude scale and zero point errors of a few tenths of a magnitude, except in the southern Coalsack, where he quoted a surface brightness that is much too faint. The legacy of Pannekoek in the area of Galactic research consists of his mapping of the structure of the nearby part of the Galaxy, the distances of dark clouds, and isophotal maps of the Milky Way. His other contributions turned out inconclusive or wrong as a result of his conviction, resulting from his many years of observing and mapping the Milky Way, that the nearby distribution is characterized primarily by more or less isolated clouds of stars and by dust restricted to isolated dark clouds and streaks. In Appendix 1 I show that the widespread notion that the center of the Galaxy is located in the constellation Sagittarius is not so compelling as usually thought and could with equal justification be placed in Scorpius. Appendix 2 provides short curriculae vitae of a few Dutch PhDs that have been referred to in this paper. [ABSTRACT FROM AUTHOR]

Spiral density waves can arise in galactic discs as linear instabilities of the underlying stellar distribution function. Such an instability grows exponentially in amplitude at some fixed growth rate β before saturating non-linearly. However, the mechanisms behind saturation, and the resulting saturated spiral amplitude, have received little attention. Here, we argue that one important saturation mechanism is the non-linear trapping of stars near the spiral's corotation resonance. Under this mechanism, we show analytically that an m -armed spiral instability will saturate when the libration frequency of resonantly trapped orbits reaches |$\omega _\mathrm{lib} \sim \mathrm{a\, \, few}\times m^{1/2} \beta$|⁠. For a galaxy with a flat rotation curve, this implies a maximum relative spiral surface density |$\vert \delta \Sigma /\Sigma _0\vert \sim \mathrm{a\, \, few} \times (\beta /\Omega _\mathrm{p})^2 \cot \alpha$|⁠ , where Ωp is the spiral pattern speed and α is its pitch angle. This result is in reasonable agreement with recent N -body simulations, and suggests that spirals driven by internally-generated instabilities reach relative amplitudes of at most a few tens of per cent; higher amplitude spirals, like in M51 and NGC 1300, are likely caused by very strong bars and/or tidal perturbations. [ABSTRACT FROM AUTHOR]

Introduction: The Multi-Channel Imager (MCI), one of the back-end modules of the future China Space Station Telescope (CSST), is designed for high-precision space-based astronomical observations. This paper evaluates the astrometric capability of the MCI based on simulated observational images and Gaia data: the M31 galaxy is selected as a representative case to validate the astrometric capability by calculating the proper motions (PMs) of the M31 member stars. Method: We analyze the stellar centroids of the simulated images in the R, I and G bands, positional uncertainty of 2.5 mas for brighter foreground reference stars from the Gaia DR3 catalog and of 7.5 mas for the fainter M31 member stars, are adopted respectively. The theoretical PMs are generated from the adopted velocity field model, rotation curve, and stellar surface density profile. And the simulated observed PMs are generated from the aforementioned position uncertainties and theoretical PMs. Result: We conclude that the precision of the MCI derived PMs strongly depends on the number of astrometric epochs per year. Specifically, uncertainty of 10 μas/yr is achievable with 10 epochs per year, and of 5 μas/yr with 50 epochs ignoring possible systematic effects. And symmetrically distributed observed fields yield better M31 kinematic parameters. Discussion: Unknown systematic errors, space environment effects on detectors, dithering strategies, and observation schedules can affect the PMs of M31, the above issues need further analysis and validation in future work. [ABSTRACT FROM AUTHOR]

Most stars form in highly clustered environments within molecular clouds, but eventually disperse into the distributed stellar field population. Exactly how the stellar distribution evolves from the embedded stage into gas-free associations and (bound) clusters is poorly understood. We investigate the long-term evolution of stars formed in the starforge simulation suite – a set of radiation-magnetohydrodynamic simulations of star-forming turbulent clouds that include all key stellar feedback processes inherent to star formation. We use nbody6++gpu to follow the evolution of the young stellar systems after gas removal. We use HDBSCAN to define stellar groups and analyse the stellar kinematics to identify the true bound star clusters. The conditions modeled by the simulations, i.e. global cloud surface densities below 0.15 g cm−2, star formation efficiencies below 15 per cent, and gas expulsion time-scales shorter than a free fall time, primarily produce expanding stellar associations and small clusters. The largest star clusters, which have ∼1000 bound members, form in the densest and lowest velocity dispersion clouds, representing ∼32 and 39 per cent of the stars in the simulations, respectively. The cloud's early dynamical state plays a significant role in setting the classical star formation efficiency versus bound fraction relation. All stellar groups follow a narrow mass-velocity dispersion power-law relation at 10 Myr with a power-law index of 0.21. This correlation result in a distinct mass–size relationship for bound clusters. We also provide valuable constraints on the gas dispersal time-scale during the star formation process and analyse the implications for the formation of bound systems. [ABSTRACT FROM AUTHOR]

The study of the chemistry of the stellar populations in globular clusters (GCs) is a fundamental task to unveil their formation in the high-redshift universe and to reconstruct the build-up of our Galaxy. Using metallicity estimates from BP/RP low-resolution Gaia DR3 spectra, a recent work presented the surprizing detection of two stellar populations with distinct metallicities in the stellar stream of the GC NGC 5904, otherwise considered a mono-metallic system. The presence of these two populations, with [Fe/H] ∼ −1.4 and [Fe/H] ∼ −2.0 dex, was taken as the evidence of a merger origin of the cluster. In this Letter, using the same data set complemented by new robust metallicity estimates, we carry out a detailed analysis of the metallicity distribution of stars belonging both to the cluster and to its stellar stream, explicitly focusing on the subtle effects of data systematics. We demonstrate that the population at [Fe/H] ∼ −2.0 dex is a data artefact due to error systematics, affecting especially faint stars. The new higher quality metallicity sample corroborates this finding, and it indicates the presence of only one population of stars with metallicity of [Fe/H] ∼ −1.3 dex, in agreement with previous literature studies. We, therefore, conclude that both NGC 5904 and its stellar stream are mono-metallic systems, and emphasize the need of carefully examining systematic effects in large and complex data. [ABSTRACT FROM AUTHOR]

A key question in galaxy evolution has been the importance of the apparent "clumpiness" of high-redshift galaxies. Until now, this property has been primarily investigated in rest-frame UV, limiting our understanding of their relevance. Are they short-lived or are they associated with more long-lived massive structures that are part of the underlying stellar disks? We use JWST/NIRCam imaging from the Cosmic Evolution and Epoch of Reionization Survey to explore the connection between the presence of these "clumps" in a galaxy and its overall stellar morphology, in a mass-complete ( log M * / M ⊙ > 10.0) sample of galaxies at 1.0 < z < 2.0. Exploiting the uninterrupted access to rest-frame optical and near-IR light, we simultaneously map the clumps in galactic disks across our wavelength coverage, along with measuring the distribution of stars among their bulges and disks. First, we find that the clumps are not limited to the rest-frame UV and optical, but are also apparent in near-IR with ∼60% spatial overlap. This rest-frame near-IR detection indicates that clumps would also feature in the stellar-mass distribution of the galaxy. A secondary consequence is that these will hence be expected to increase the dynamical friction within galactic disks leading to gas inflow. We find a strong negative correlation between how clumpy a galaxy is and strength of the bulge. This firmly suggests an evolutionary connection, either through clumps driving bulge growth or the bulge stabilizing the galaxy against clump formation, or a combination of the two. Finally, we find evidence of this correlation differing from rest-frame optical to near-IR, which could suggest a combination of varying formation modes for the clumps. [ABSTRACT FROM AUTHOR]

This paper describes the extended data release (eDR) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. It comprises science-grade quality data for 895 galaxies obtained with the Potsdam Multi Aperture Spectograph/PPak instrument at the 3.5-m telescope at the Calar Alto Observatory along the last 12 yr, using the V500 setup [3700–7500 Å, 6 Å/full-width at half-maximum (FWHM)] and the CALIFA observing strategy. It includes galaxies of any morphological type, star formation stage, a wide range of stellar masses (∼107–1012 M⊙), at an average redshift of ∼0.015 (90 per cent within 0.005 < z < 0.05). Primarily selected based on the projected size and apparent magnitude, we demonstrate that it can be volume corrected resulting in a statistically limited but representative sample of the population of galaxies in the nearby Universe. All the data were homogeneous re-reduced, introducing a set of modifications to the previous reduction. The most relevant is the development and implementation of a new cube-reconstruction algorithm that provides with an (almost) seeing-limited spatial resolution (FWHMPSF ∼ 1.0 arcsec). To illustrate the usability and quality of the data, we extracted two aperture spectra for each galaxy (central 1.5 arcsec and fully integrated), and analyse them using pyFIT3D. We obtain a set of observational and physical properties of both the stellar populations and the ionized gas, that have been compared for the two apertures, exploring their distributions as a function of the stellar masses and morphologies of the galaxies, comparing with recent results in the literature. [ABSTRACT FROM AUTHOR]

We investigate the stochastic gravitational-wave background (SGWB) produced by merging binary black holes (BBHs) and binary neutron stars (BNSs) in the frequency ranges of Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo/Kagra and Laser Interferometer Space Antenna (LISA). We develop three analytical models, which are calibrated to the measured local merger rates, and complement them with three population synthesis models based on the cosmic code. We discuss the uncertainties, focusing on the impact of the BBH mass distribution, the effect of the metallicity of the progenitor stars, and the time delay distribution between star formation and compact binary merger. We also explore the effect of uncertainties in binary stellar evolution on the background. For BBHs, our analytical models predict ΩGW in the range [4 × 10−10 to 1 × 10−9] (25 Hz) and [1 × 10−12 to 4 × 10−12] (3 mHz), and between [2 × 10−10 to 2 × 10−9] (25 Hz) and [7 × 10−13 to 7 × 10−12] (3 mHz) for our population synthesis models. This background is unlikely to be detected during the LIGO/Virgo/Kagra O4 run, but could be detectable with LISA. We predict about 10 BBH and no BNS mergers that could be individually detectable by LISA for a period of observation of 4 yr. Our study provides new insights into the population of compact binaries and the main sources of uncertainty in the astrophysical SGWB. [ABSTRACT FROM AUTHOR]

We obtain the kinematic distributions of stars (synthetic model line absorption) and ionized gas (H α line emission) for star-forming regions residing in Calar Alto Legacy Integral Field Area survey tidally perturbed (perturbed) and non-tidally perturbed (control) galaxies. We set the uncertainties of the velocity dispersion by measuring the statistical variability of the data sets themselves. Using these adopted uncertainties and considering the sensitivity of the grating device, we establish thresholds of reliability that allow us to select reliable velocity dispersions. From this selection, we pair the star-forming spaxels between control and perturbed galaxies at the closest shifts in velocity (de-redshifting). We compare their respective distributions of velocity dispersion. In perturbed galaxies, median velocity dispersions for the stellar and gaseous components are minimally higher and equal, respectively, than those in control galaxies. The spread in velocity dispersion and the velocity shift–velocity dispersion space agree with this result. Unlike the well-known trend in strongly interacting systems, the stellar and ionized-gas motions are not disturbed by the influence of close companions. For the gaseous component, this result is due to the poor statistical variability of its data, a consequence of the tightness in velocity dispersion derived from high spectral line intensities. This analysis concludes the series, which previously showed star-forming regions in galaxies with close companions undergoing more prominent gas inflows, resulting in differences in their star formation and consequent metal content. [ABSTRACT FROM AUTHOR]

In the Milky Way, the distribution of stars in the [α/Fe] versus [Fe/H] and [Fe/H] versus age planes holds essential information about the history of star formation, accretion, and dynamical evolution of the Galactic disc. We investigate these planes by applying novel statistical methods called copulas and elicitable maps to the ages and abundances of red giants in the Apache Point Observatory Galactic Evolution Experiment survey. We find that the high- and low-α disc stars have a clean separation in copula space and use this to provide an automated separation of the α sequences using a purely statistical approach. This separation reveals that the high-α disc ends at the same [α/Fe] and age at high [Fe/H] as the low-[Fe/H] start of the low-α disc, thus supporting a sequential formation scenario for the high- and low-α discs. We then combine copulas with elicitable maps to precisely obtain the correlation between stellar age τ and metallicity [Fe/H] conditional on Galactocentric radius R and height z in the range 0 < R < 20 kpc and | z | < 2 kpc. The resulting trends in the age–metallicity correlation with radius, height, and [α/Fe] demonstrate a ≈0 correlation wherever kinematically cold orbits dominate, while the naively expected negative correlation is present where kinematically hot orbits dominate. This is consistent with the effects of spiral-driven radial migration, which must be strong enough to completely flatten the age–metallicity structure of the low-α disc. [ABSTRACT FROM AUTHOR]

The |$\rm {H}\alpha$| -to-UV luminosity ratio (⁠|$L(\text{H}\alpha)/L(\rm UV)$|⁠) is often used to probe bursty star formation histories (SFHs) of star-forming galaxies and it is important to validate it against other proxies for burstiness. To address this issue, we present a statistical analysis of the resolved distribution of star formation rate surface density (ΣSFR) as well as stellar age and their correlations with the globally measured |$L(\text{H}\alpha)/L(\rm UV)$| for a sample of 310 star-forming galaxies in two redshift bins of 1.37 < z < 1.70 and 2.09 < z < 2.61 observed by the MOSFIRE Deep Evolution Field (MOSDEF) survey. We use the multiwaveband CANDELS/3D-HST imaging of MOSDEF galaxies to construct ΣSFR and stellar age maps. We analyse the composite rest-frame far-ultraviolet spectra of a subsample of MOSFIRE Deep Evolution Field (MOSDEF) targets obtained by the Keck Low Resolution Imager and Spectrometer (LRIS), which includes 124 star-forming galaxies (MOSDEF-LRIS) at redshifts 1.4 < z < 2.6, to examine the average stellar population properties, and the strength of age-sensitive far-ultraviolet spectral features in bins of |$L(\text{H}\alpha)/L(\rm UV)$|⁠. Our results show no significant evidence that individual galaxies with higher |$L(\text{H}\alpha)/L(\rm UV)$| are undergoing a burst of star formation based on the resolved distribution of ΣSFR of individual star-forming galaxies. We segregate the sample into subsets with low and high |$L(\text{H}\alpha)/L(\rm UV)$|⁠. The high- |$L(\text{H}\alpha)/L(\rm UV)$| subset exhibits, on average, an age of |$\log [\rm {Age/yr}]$|  = 8.0, compared to |$\log [\rm {Age/yr}]$| = 8.4 for the low- |$L(\text{H}\alpha)/L(\rm UV)$| galaxies, though the difference in age is significant at only the 2σ level. Furthermore, we find no variation in the strengths of Si  iv λλ1393, 1402 and C  iv λλ1548, 1550 P-Cygni features from massive stars between the two subsamples, suggesting that the high- |$L(\text{H}\alpha)/L(\rm UV)$| galaxies are not preferentially undergoing a burst compared to galaxies with lower |$L(\text{H}\alpha)/L(\rm UV)$|⁠. On the other hand, we find that the high- |$L(\text{H}\alpha)/L(\rm UV)$| galaxies exhibit, on average, more intense He  ii λ1640 emission, which may possibly suggest the presence of a higher abundance of high-mass X-ray binaries. [ABSTRACT FROM AUTHOR]

Large-scale asymmetries (i.e. lopsidedness) are a common feature in the stellar density distribution of nearby disc galaxies both in low- and high-density environments. In this work, we characterize the present-day lopsidedness in a sample of 1435 disc-like galaxies selected from the TNG50 simulation. We find that the percentage of lopsided galaxies (10  per cent–30  per cent) is in good agreement with observations if we use similar radial ranges to the observations. However, the percentage (58  per cent) significantly increases if we extend our measurement to larger radii. We find a mild or lack of correlation between lopsidedness amplitude and environment at z  = 0 and a strong correlation between lopsidedness and galaxy morphology regardless of the environment. Present-day galaxies with more extended discs, flatter inner galactic regions, and lower central stellar mass density (i.e. late-type disc galaxies) are typically more lopsided than galaxies with smaller discs, rounder inner galactic regions, and higher central stellar mass density (i.e. early-type disc galaxies). Interestingly, we find that lopsided galaxies have, on average, a very distinct star formation history within the last |$10\, \mathrm{Gyr}$|⁠ , with respect to their symmetric counterparts. Symmetric galaxies have typically assembled at early times (∼8– |$6\, \mathrm{Gyr}$| ago) with relatively short and intense bursts of central star formation, while lopsided galaxies have assembled on longer time-scales and with milder initial bursts of star formation, continuing building up their mass until z  = 0. Overall, these results indicate that lopsidedness in present-day disc galaxies is connected to the specific evolutionary histories of the galaxies that shaped their distinct internal properties. [ABSTRACT FROM AUTHOR]

We use the Subaru Hyper Suprime-Cam (HSC) data to study structural parameters and systemic proper motion of the Sextans dwarf spheroidal galaxy at the heliocentric distance of 86 kpc, which is one of the most important targets for studies of dark matter nature and galaxy formation physics. Thanks to the superb image quality and wide area coverage, the HSC data enable a secure selection of member star candidates based on the colour–magnitude cut, yielding about 10 000 member candidates at magnitudes down to i ∼ 24. We use a likelihood analysis of the two-dimensional distribution of stars to estimate the structural parameters of Sextans taking into account the contamination of foreground halo stars in the Milky Way, and find that the member star distribution is well fitted by an elliptical King profile with ellipticity ϵ ≃ 0.25 and the core and tidal radii of R c = (368.4 ± 8.5) pc and R t = (2.54 ± 0.046) kpc, respectively. Then using the two HSC data sets of 2.66 yr time baseline on average, we find the systemic proper motions of Sextans to be (μα, μδ) = (−0.448 ± 0.075, 0.058 ± 0.078) mas yr−1, which are consistent with some of the previous works using the Gaia data of relatively bright member stars in Sextans. Thus, our results give a demonstration that ground-based, large-aperture telescope data that cover a wide solid angle of the sky and have a long time baseline, such as the upcoming data from Legacy Survey of Space and Time (LSST), can be used to study systemic proper motions of dwarf galaxies. [ABSTRACT FROM AUTHOR]

We use two cosmological simulations to study the impact of spurious heating of stellar motions within simulated galaxies by dark matter (DM) particles. The simulations share the same numerical and subgrid parameters, but one used a factor of 7 more DM particles. Many galaxy properties are unaffected by spurious heating, including their masses, star formation histories, and the spatial distribution of their gaseous baryons. The distribution and kinematics of stellar and DM particles, however, are affected. Below a resolution-dependent virial mass, |$M_{200}^{\rm spur}$|⁠ , galaxies have higher characteristic velocities, larger sizes, and more angular momentum in the simulation with lower DM mass resolution; haloes have higher central densities and lower velocity dispersions. Above |$M_{200}^{\rm spur}$|⁠ , galaxies and haloes have similar properties in both runs. The differences arise due to spurious heating, which transfers energy from DM to stellar particles, causing galaxies to heat up and haloes to cool down. The value of |$M_{200}^{\rm spur}$| can be derived from an empirical disc heating model, and coincides with the mass below which the predicted spurious velocity dispersion exceeds the measured velocity dispersion of simulated galaxies. We predict that galaxies in the |$100^3\, {\rm Mpc}^3$| eagle  run and IllustrisTNG-100 are robust to spurious collisional effects at their half-mass radii provided |$M_{200}^{\rm spur}\approx 10^{11.7}\, {\rm M_\odot }$|⁠ ; for the |$25^3\, {\rm Mpc}^3$| eagle  run and IllustrisTNG-50, we predict |$M_{200}^{\rm spur}\approx 10^{11}\, {\rm M_\odot }$|⁠. Suppressing spurious heating at smaller/larger radii, or for older/younger stellar populations, requires haloes to be resolved with more/fewer DM particles. [ABSTRACT FROM AUTHOR]

The unexpected discovery of hot Jupiters challenged the classical theory of planet formation inspired by our solar system. Until now, the origin and evolution of hot Jupiters are still uncertain. Determining their age distribution and temporal evolution can provide more clues into the mechanism of their formation and subsequent evolution. Using a sample of 383 giant planets around Sun-like stars collected from the kinematic catalogs of the Planets Across Space and Time project, we find that hot Jupiters are preferentially hosted by relatively younger stars in the Galactic thin disk. We subsequently find that the frequency of hot Jupiters declines with age as FHJ / exp(-0:20 ± 0:06 ± t Gyr). In contrast, the frequency of warm/cold Jupiters shows no significant dependence on age. Such a trend is expected from the tidal evolution of hot Jupiters' orbits, and our result offers supporting evidence using a large sample. We also perform a joint analysis on the planet frequencies in the stellar agemetallicity plane. The result suggests that the frequencies of hot Jupiters and warm/cold Jupiters, after removing the age dependence are both correlated with stellar metallicities as FHJ / 101:6+0:3 -0:3-[Fe=H] and FWJ=CJ / 101:1+0:2 -0:3-[Fe=H], respectively. Moreover, we show that the above correlations can explain the bulk of the discrepancy in hot Jupiter frequencies inferred from the transit and radial velocity (RV) surveys, given that RV targets tend to be more metal-rich and younger than transits. [ABSTRACT FROM AUTHOR]

A specimen belonging to the deep-sea feather-star family Atelecrinidae was collected in April 2018 at the Kocebu Guyot at 1294 m deep. Based on its morphological characters, the specimen was identified as Paratelecrinus cubensis (Carpenter, 1881). This species of feather star is restricted to the deep sea and was known only from 12 records from the Bahamas and Cuba at depths of 567-892 m. The data represent the first record from the Western Pacific Ocean and the deepest record known, extending the depth where this feather star has been found to beyond 1000 m. The morphological characteristics of the Kocebu Guyot specimen were essentially identical to the morphology of the neotype, with a slight difference in the dorsal spine at the end of the cirri. The phylogenetic analysis based on the mitochondrial cytochrome c oxidase subunit I (COI), 16S rRNA genes, 28S rRNA genes, and 18S rRNA genes reveal a close relationship of P. cubensis with P. wyvilli. Results of our molecular phylogenetic analysis are consistent with our morphological identifications. Our find extends the known geographical distribution of the feather star P. cubensis to the Western Pacific Ocean and provide insights into deep-sea biodiversity in the Kocebu Guyot. [ABSTRACT FROM AUTHOR]

Anomalously high nitrogen-to-oxygen abundance ratios [N/O] are observed in globular clusters (GCs), among the field stars of the Milky Way (MW), and even in the gas in a z ≈ 11 galaxy. Using data from the APOGEE Data Release 17 and the Gaia Data Release 3, we present several independent lines of evidence that most of the MW's high-[N/O] stars were born in situ in massive bound clusters during the early, pre-disc evolution of the Galaxy. Specifically, we show that distributions of metallicity [Fe/H], energy, the angular momentum Lz , and distance of the low-metallicity high-[N/O] stars match the corresponding distributions of stars of the Aurora population and of the in situ GCs. We also show that the fraction of in situ field high-[N/O] stars, f N/O, increases rapidly with decreasing metallicity. During epochs when metallicity evolves from |$\rm [Fe/H]=-1.5$| to |$\rm [Fe/H]=-0.9$|⁠ , the Galaxy spins up and transitions from a turbulent Aurora state to a coherently rotating disc. This transformation is accompanied by many qualitative changes. In particular, we show that high N/O abundances similar to those observed in GN-z11 were common before the spin-up (⁠|$\rm [Fe/H]\lesssim -1.5$|⁠) when up to |$\approx 50~{{\ \rm per\ cent}}-70~{{\ \rm per\ cent}}$| of the in situ stars formed in massive bound clusters. The dramatic drop of f N/O at |$\rm [Fe/H]\gtrsim -0.9$| indicates that after the disc emerges the fraction of stars forming in massive bound clusters decreases by two orders of magnitude. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the structure of the Local Group flocculent spiral galaxy M33, as measured using the Panchromatic Hubble Andromeda Treasury Triangulum Extended Region (PHATTER) survey. Leveraging the multiwavelength coverage of PHATTER, we find that the oldest populations are dominated by a smooth exponential disk with two distinct spiral arms and a classical central bar—completely distinct from what is seen in broadband optical imaging, and the first-ever confirmation of a bar in M33. We estimate a bar extent of ∼1 kpc. The two spiral arms are asymmetric in orientation and strength, and likely represent the innermost impact of the recent tidal interaction responsible for M33's warp at larger scales. The flocculent multiarmed morphology for which M33 is known is only visible in the young upper main-sequence population, which closely tracks the morphology of the interstellar medium. We investigate the stability of M33's disk, finding Q ∼ 1 over the majority of the disk. We fit multiple components to the old stellar density distribution and find that, when considering recent stellar kinematics, M33's bulk structure favors the inclusion of an accreted halo component, modeled as a broken power law. The best-fit halo has an outer power-law index of −3 and accurately describes observational evidence of M33's stellar halo from both resolved stellar spectroscopy in the disk and its stellar populations at large radius. Integrating this profile yields a total halo stellar mass of ∼5 × 108 M ⊙, for a stellar halo mass fraction of 16%, most of which resides in the innermost 2.5 kpc. [ABSTRACT FROM AUTHOR]

We present the first study of spatially integrated higher-order stellar kinematics over cosmic time. We use deep rest-frame optical spectroscopy of quiescent galaxies at redshifts z  = 0.05, 0.3, and 0.8 from the SAMI, MAGPI, and LEGA-C surveys to measure the excess kurtosis h 4 of the stellar velocity distribution, the latter parametrized as a Gauss-Hermite series. Conservatively using a redshift-independent cut in stellar mass (⁠|$M_\star = 10^{11}\, \mathrm{M_\odot }$|⁠) and matching the stellar-mass distributions of our samples, we find 7σ evidence of h 4 increasing with cosmic time, from a median value of 0.019 ± 0.002 at z  = 0.8 to 0.059 ± 0.004 at z  = 0.06. Alternatively, we use a physically motivated sample selection based on the mass distribution of the progenitors of local quiescent galaxies as inferred from numerical simulations; in this case, we find 10σ evidence. This evolution suggests that, over the last 7 Gyr, there has been a gradual decrease in the rotation-to-dispersion ratio and an increase in the radial anisotropy of the stellar velocity distribution, qualitatively consistent with accretion of gas-poor satellites. These findings demonstrate that massive galaxies continue to accrete mass and increase their dispersion support after becoming quiescent. [ABSTRACT FROM AUTHOR]

The dominant formation mechanism of brown dwarfs and planetary-mass objects (PMOs) in star-forming regions is presently uncertain. Do they form like stars, via the collapse and fragmentation of cores in giant molecular clouds, or do they form like planets in the discs around stars and are ejected via dynamical interactions? In this paper, we quantify the spatial distribution of substellar objects in NGC 1333, in particular focusing on PMOs that have been the target of recent deep imaging observations. We find that these objects have a spatial distribution that is indistinguishable from the stars, and more massive brown dwarfs. We also analyse N -body simulations and find that a population of ejected planets would have a significantly different spatial and kinematic distribution from stars, and brown dwarfs that also formed through gravitational collapse and fragmentation. We therefore conclude that the low-mass substellar objects in NGC 1333 formed more like stars than planets, although we predict that a population of hitherto undetected ejected PMOs may be lurking in this and other star-forming regions. [ABSTRACT FROM AUTHOR]

We propose a new method for measuring the spatial density distribution of the stellar halo of the Milky Way. Our method is based on a pairwise statistic of the distribution of stars in the sky, the angular two-point correlation function (ATPCF). The ATPCF utilizes two-dimensional data of stars only and is therefore immune to the large uncertainties in the determination of distances to stars. We test our method using mock stellar data coming from various models including the single power-law (SPL) and the broken power-law (BPL) density profiles. We also test the influence of axisymmetric flattening factors using both constant and varying values. We find that the ATPCF is a powerful tool for recovering the spatial distributions of the stellar haloes in our models. We apply our method to observational data from the type ab RR Lyrae catalogue in the Catalina Survey Data Release 1. In the 3-parameter BPL model, we find that |$s_{1}=2.46_{-0.20}^{+0.18}, s_{2}=3.99_{-1.33}^{+0.75}$|⁠ , and |$r_{0}=31.11_{-5.88}^{+7.61}$|⁠ , which are in good agreement with previous results. We also find that introducing an extra parameter, the radially varying flattening factor, greatly improves our ability to model accurately the observed data distribution. This implies perhaps that the stellar halo of the Milky Way should be regarded as oblate. [ABSTRACT FROM AUTHOR]

We present the first statistical study of spatially integrated non-Gaussian stellar kinematics spanning 7 Gyr in cosmic time. We use deep, rest-frame optical spectroscopy of massive galaxies (stellar mass |$M_\star \gt 10^{10.5} \, \mathrm{M_\odot }$|⁠) at redshifts z = 0.05, 0.3, and 0.8 from the SAMI, MAGPI, and LEGA-C surveys, to measure the excess kurtosis h 4 of the stellar velocity distribution, the latter parametrized as a Gauss–Hermite series. We find that at all redshifts where we have large enough samples, h 4 anticorrelates with the ratio between rotation and dispersion, highlighting the physical connection between these two kinematic observables. In addition, and independently from the anticorrelation with rotation-to-dispersion ratio, we also find a correlation between h 4 and M ⋆, potentially connected to the assembly history of galaxies. In contrast, after controlling for mass, we find no evidence of independent correlation between h 4 and aperture velocity dispersion or galaxy size. These results hold for both star-forming and quiescent galaxies. For quiescent galaxies, h 4 also correlates with projected shape, even after controlling for the rotation-to-dispersion ratio. At any given redshift, star-forming galaxies have lower h 4 compared to quiescent galaxies, highlighting the link between kinematic structure and star-forming activity. [ABSTRACT FROM AUTHOR]

This work explores the mixing rate of metals in the interstellar medium (ISM), comparing observational constraints from our solar neighbourhood to high resolution cosmological hydrodynamical simulations of Milky Way (MW)-like galaxies. The mixing rate, described by the coefficient C, is varied in simulations between 0 and 0.05, with resultant simulated galaxies compared to observations of metallicity dispersion in young star clusters, H ii regions and neutral gas in the disc of the MW. A value of C between 0.003125 and 0.0125 is found to self-consistently match a range of observables, with a best estimate of C = 0.0064 ± 0.0004. We demonstrate that the relationship between metal dispersion in young stars, H ii regions and neutral gas, versus the coefficient C, can be described by a power law. These constrained mixing rates infer a comparatively well-mixed ISM in the solar neighbourhood, at odds with some recent observations that have reported a highly inhomogeneous ISM. The degree of mixing suggested by this work is lower than what often employed in many hydrodynamical simulations. Our results have implications for studying the metallicity distribution of stars as well as of gas in the interstellar and circum-galactic media. [ABSTRACT FROM AUTHOR]

We use the GRUMPY galaxy formation model based on a suite of zoom-in, high-resolution, dissipationless Λ Cold Dark Matter (ΛCDM) simulations of the Milky Way (MW) sized haloes to examine total matter density within the half-mass radius of stellar distribution, ρtot(< r 1/2), of satellite dwarf galaxies around the MW hosts and their mass assembly histories. We compare model results to ρtot(< r 1/2) estimates for observed dwarf satellites of the Milky Way spanning their entire luminosity range. We show that observed MW dwarf satellites exhibit a trend of decreasing total matter density within a half-mass radius, ρtot(< r 1/2), with increasing stellar mass. This trend is in general agreement with the trend predicted by the model. None of the observed satellites are overly dense compared to the results of our ΛCDM-based model. We also show that although the halo mass of many satellite galaxies is comparable to the halo mass of the MW progenitor at z ≳ 10, at these early epochs halos that survive as satellites to z  = 0 are located many virial radii away from the MW progenitors and thus do not have a chance to merge with it. Our results show that neither the densities estimated in observed Milky Way satellites nor their mass assembly histories pose a challenge to the ΛCDM model. In fact, the broad agreement between density trends with the stellar mass of the observed and model galaxies can be considered as yet another success of the model. [ABSTRACT FROM AUTHOR]

To accurately link the radio and optical Celestial Reference Frames (CRFs) at optical bright end, i.e. with GaiaG -band magnitude |$\lesssim$| 13, increasing number and improving sky distribution of radio stars with accurate astrometric parameters from both Very Long Baseline Interferometry (VLBI) and Gaia measurements are mandatory. We selected two radio stars HD 199178 and AR Lacertae as the target for a pilot program for the frame link, using the Very Long Baseline Array at 15 GHz at six epochs spanning about 1 yr, to measure their astrometric parameters. The measured parallax of HD 199178 is 8.949 ± 0.059 mas and the proper motion is μ αcos δ = 26.393 ± 0.093 and μ δ = −0.950 ± 0.083 mas yr−1, while the parallax of AR Lac is 23.459 ± 0.094 mas and the proper motion is μ αcos δ = −51.906 ± 0.138 and μ δ = 46.732 ± 0.131 mas yr−1. Our VLBI measured astrometric parameters have accuracies about 4–5 times better than the corresponding historic VLBI measurements and comparable accuracies with those from Gaia , validating the feasibility of frame link using radio stars. With the updated astrometric parameters for these two stars, there is a ∼25 per cent reduction of the uncertainties on the Y -axis for both orientation and spin parameters. [ABSTRACT FROM AUTHOR]

Detailed analysis of kinematics of the Milky Way disk in the solar neighborhood based on the GAIA DR3 catalog reveals the existence of peculiarities in the stellar velocity distribution perpendicular to the galactic plane. We study the influence of resonances—the outer Lindblad resonance and the outer vertical Lindblad resonance—of a rotating bar with stellar oscillations perpendicular to the plane of the disk, and their role in shaping the spatial and the velocity distributions of stars. We find that the Z and V Z distributions of stars with respect to L Z are affected by the outer Lindblad resonance. The existence of bar resonance with stellar oscillations perpendicular to the plane of the disk is demonstrated for a long (large semi-axis 5 kpc) and fast rotating bar with Ω b = 60.0 km s − 1 kpc − 1 . We show also that, in the model with the long and fast rotating bar, some stars in the 2:1 OLR region deviate far from their original places, entering the bar region. A combination of resonance excitation of stellar motions at the 2:1 OLR region together with strong interaction of the stars with the bar potential leads to the formation of the group of 'escapees', i.e., stars that deviate in R and Z—directions at large distances from the resonance region. Simulations, however, do not demonstrate any noticeable effect on V Z -distribution of stars in the solar neighborhood. [ABSTRACT FROM AUTHOR]

Using data from the Gaia satellite's Radial Velocity Spectrometer Data Release 3 (RVS, DR3), we find a new and robust feature in the phase-space distribution of halo stars. It is a prominent ridge at constant energy and with angular momentum Lz > 0. We run test particle simulations of a stellar halo-like distribution of particles in a realistic Milky Way potential with a rotating bar. We observe similar structures generated in the simulations from the trapping of particles in resonances with the bar, particularly at the corotation resonance. Many of the orbits trapped at the resonances are halo like, with large vertical excursions from the disc. The location of the observed structure in energy space is consistent with a bar pattern speed in the range Ωb ≈ 35−40 km s−1 kpc−1. Overall, the effect of the resonances is to give the inner stellar halo a mild, net spin in the direction of the bar's rotation. As the distribution of the angular momentum becomes asymmetric, a population of stars with positive mean Lz and low vertical action is created. The variation of the average rotational velocity of the simulated stellar halo with radius is similar to the behaviour of metal-poor stars in data from the APOGEE survey. Though the effects of bar resonances have long been known in the Galactic disc, this is strong evidence that the bar can drive changes even in the diffuse and extended stellar halo through its resonances. [ABSTRACT FROM AUTHOR]

M-dwarfs are common stellar hosts of habitable-zone exoplanets. Near-UV (NUV) radiation can severely impact the atmospheric and surface conditions of such planets, making the characterization of NUV flaring activity a key aspect in determining habitability. We use archival data from the Galaxy Evolution Explorer (GALEX) and XMM-Newton telescopes to study the flaring activity of M-dwarfs in the NUV. The GALEX observations form the most extensive data set of M-dwarfs in the NUV to date, with the exploitation of this data possible due to the new g photon 2 pipeline. We run a dedicated algorithm to detect flares in the pipeline-produced lightcurves and find some of the most energetic flares observed to date within the NUV bandpass, with energies of ∼1034 erg. Using GALEX data, we constrain flare frequency distributions for stars from M0-M6 in the NUV up to 105 s in equivalent duration and 1034 erg in energy, orders of magnitude above any previous study in the UV. We estimate the combined effect of NUV luminosities and flare rates of stars later than M2 to be sufficient for abiogenesis on habitable-zone exoplanets orbiting them. As a counterpoint, we speculate the high frequencies of energetic UV flares and associated coronal mass ejections would inhibit the formation of an ozone layer, possibly preventing the genesis of complex Earth-like life-forms due to sterilizing levels of surface UV radiation. We also provide a framework for future observations of M-dwarfs with ULTRASAT, a wide field-of-view NUV telescope to be launched in 2026. [ABSTRACT FROM AUTHOR]

We present an analysis of major-axis surface-brightness profiles of bars in a volume-limited sample of 182 barred spiral galaxies, using Spitzer 3.6  |$\mu$| m images. Unlike most previous studies, we use the entire bar profile, and we classify profiles into four categories. These are 'Peak+Shoulders' (P+Sh) – updating the classic 'flat bar' profile – and three subtypes of the classic 'exponential' profile: (true) Exponential, 'Two-Slope' (shallow inner slope + steeper outer slope), and 'Flat-Top' (constant inner region, steep outer slope). P+Sh profiles are preferentially found in galaxies with high stellar masses, early Hubble types, red colours, and low gas fractions; the most significant factor is stellar mass, and previous correlations with Hubble type can be explained by the tendency of higher-mass galaxies to have earlier Hubble types. The most common type of non-P+Sh profile is Exponential, followed by Flat-Top profiles; all non-P+Sh profiles appear to have similar distributions of stellar mass, Hubble type, colour, and gas fraction. We also morphologically classify the bars of an inclined subsample into those with and without boxy/peanut-shaped (B/P) bulges; as previously reported, the presence of a B/P bulge is very strong function of stellar mass. Essentially all bars with B/P bulges have P+Sh profiles; we associate the profile shoulders with the outer, vertically thin part of the bar. We find a small number of P+Sh profiles in bars without clear B/P bulges, which may indicate that P+Sh formation precedes the formation of B/P bulges. [ABSTRACT FROM AUTHOR]

We present a new dust extinction technique with which we are able to retrieve parsec-scale gas surface density maps for entire nearby galaxies. The method measures the dust attenuation in optical bands on a pixel-by-pixel basis against a smoothed, reconstructed stellar distribution. The contribution of foreground light along the line-of-sight is calibrated using dust emission observations, assuming that the dust sits in a layer close to the mid-plane of the face-on galaxy. Here, we apply this technique to M51 (NGC 5194) as a proof-of-concept, obtaining a resolution of 0.14 arcsec (5 pc). Our dust (and gas) surface density map is consistent with independent dust- and CO-based studies at lower resolution. We find that discrepancies between our estimates of surface density and other studies stem primarily from the choice of dust model (i.e. different dust absorption coefficients). When assuming the same dust opacity law, our technique produces surface densities that are consistent with independent studies. This dust extinction technique provides us with gas surface density maps at an unprecedented resolution for full disc coverage studies of nearby galaxies. The resulting well-resolved spatial information opens the possibility for more in-depth examination of the influence of large-scale dynamics (and also stellar feedback mechanisms) on the interstellar medium at parsec-scales, and consequently star formation in nearby galaxies. [ABSTRACT FROM AUTHOR]

In this concluding work of the series, a sample of selected ∼ 20 , 000 type-ab RR Lyrae stars from a total of 39,617 sources of the old bulge at distances r < 3.5 kpc from the Galactic Centre (GC) identified in the Vista Variables in the Vía Láctea survey (VVV) via the latest sample of the VIrac VAriable Classification Ensemble (VIVACE) pipeline is leveraged. As a model of the bulge, an oblate spheroid of stars with two major perpendicular axes a and b situated in the Galactic plane and a minor axis c perpendicular to this plane is adopted. The spatial distribution of stars is approximated by a standard power law with constant flattening and truncations at the lower and upper limits while allowing for the Sun's distance from the GC r 0 , the power-law index α , and the oblateness q = c / a to be free parameters. Our estimate of the distance is r 0 = 8.15 ± 0.04 kpc. The implied r 0 is almost the same for 1.5 < r max < 3.5 kpc, while the | α | and q values are varying systematically with increasing truncation radius r max in the ranges 1.56 − 2.66 and 1.0 − 0.76 . A weighted average and weighted uncertainty associated with all our measurements of r 0 in the series is also taken, r 0 = 8.2 ± 0.1 kpc. We argue that the ensuing result may be among the most robust indirect estimates that exist, as certain of the findings are tied to passbands of the Optical Gravitational Lensing Experiment (OGLE) RR Lyraes and globular clusters, and to near-infrared passbands of the VVV Type II Cepheids and VIVACE-VVV RR Lyraes. The distribution of stars within ≈ 3 kpc from the GC is spherical-like, q ≈ 1 . The average power-law indexes derived from the distribution of bulge RRab and inner halo globular clusters are nearly identical. This pertinent result demonstrates that the old bulge and inner halo form a continuous subsystem, and the bulk of the bulge objects represents the inner extension of a centrally concentrated, almost axisymmetric halo in the Galaxy. [ABSTRACT FROM AUTHOR]

Aims. We aim to compute the binary fraction of "classical" dwarf spheroidal galaxies (dSphs) that are satellites of the Milky Way (MW). This value can offer insights into the binary fraction in environments that are less dense and more metal-poor than our own galaxy. Additionally, knowledge of the binary fraction in dwarf galaxies is important with respect to avoiding overestimations of their dark matter content, inferred from stellar kinematics. Methods. We refined an existing method from the literature, placing an emphasis on providing robust uncertainties on the value of the binary fraction. We applied this modified method to a VLT/FLAMES dataset for Sculptor, specifically acquired for the purpose of velocity monitoring of individual stars, as well as to literature datasets for other six MW "classical" dSphs. In all cases, the targeted stars were mainly red giant branch stars, with expected masses of around 0.8 M⊙. The VLT/FLAMES dataset offers the most precise binary fractions compared to literature datasets, due to its time baseline of 12 yr, along with at least nine repeated observations for each star. Results. We found that the binary fraction of Sculptor is 0.55−0.19+0.17. We find that it is important to take into account the Roche lobe overflow for constraining the period distribution of binary stars. In contrast to what has recently been proposed in the literature, our analysis indicates that there is no evidence to support varying the properties of the binary stellar population or their deviations from those established for the solar neighborhood, based on the sample of MW dSphs analyzed here. [ABSTRACT FROM AUTHOR]

Context. The upcoming generation of optical spectrographs on four meter-class telescopes, with their huge multiplexing capabilities, excellent spectral resolution, and unprecedented wavelength coverage, will provide high-quality spectra for thousands of galaxies. These data will allow us to examine of the stellar population properties at intermediate redshift, an epoch that remains unexplored by large and deep surveys. Aims. We assess our capability to retrieve the mean stellar metallicity in galaxies at different redshifts and signal-to-noise ratios (S/N), while simultaneously exploiting the ultraviolet (UV) and optical rest-frame wavelength coverage. Methods. The work is based on a comprehensive library of spectral templates of stellar populations, covering a wide range of age and metallicity values and built assuming various star formation histories, to cover an observable parameter space with diverse chemical enrichment histories and dust attenuation. We took into account possible observational errors, simulating realistic observations of a large sample of galaxies carried out with WEAVE at the William Herschel Telescope at different redshifts and S/N values. We measured all the available and reliable indices on the simulated spectra and on the comparison library. We then adopted a Bayesian approach to compare the two sets of measurements in order to obtain the probability distribution of stellar metallicity with an accurate estimate of the uncertainties. Results. The analysis of the spectral indices has shown how some mid-UV indices, such as BL3580 and Fe3619, can provide reliable constraints on stellar metallicity, along with optical indicators. The analysis of the mock observations has shown that even at S/N = 10, the metallicity can be derived within 0.3 dex, in particular, for stellar populations older than 2 Gyr. The S/N value plays a crucial role in the uncertainty of the estimated metallicity and so, the differences between S/N = 10 and S/N = 30 are quite large, with uncertainties of ~0.15 dex in the latter case. On the contrary, moving from S/N = 30 to S/N = 50, the improvement on the uncertainty of the metallicity measurements is almost negligible. Our results are in good agreement with other theoretical and observational works in the literature and show how the UV indicators, coupled with classic optical ones, can be advantageous in constraining metallicities. Conclusions. We demonstrate that a good accuracy can be reached on the spectroscopic measurements of the stellar metallicity of galaxies at intermediate redshift, even at low S/N, when a large number of indices can be employed, including some UV indices. This is very promising for the upcoming surveys carried out with new, highly multiplexed, large-field spectrographs, such as StePS at the WEAVE and 4MOST, which will provide spectra of thousands of galaxies covering large spectral ranges (between 3600 and 9000 Å in the observed frame) at relatively high S/N (>10 Å−1). [ABSTRACT FROM AUTHOR]

Aims. We extend the classical formulation of the dynamical friction effect on a test star by Chandrasekhar to the case of relativistic velocities and velocity distributions, also accounting for post-Newtonian corrections to the gravitational force. Methods. The original kinetic framework was revised and used to construct a special-relativistic dynamical friction formula where the relative velocity changes in subsequent encounters are added up with Lorentz transformation, and the velocity distribution of the field stars accounts for relativistic velocities. Furthermore, a simple expression is obtained for systems where the post-Newtonian correction on the gravitational forces become relevant even at non-relativistic particle velocities. Finally, using a linearized Lagrangian we derived another expression for the dynamical friction expression in a more compact form than previously used. Results. Comparing our formulation with the classical one, we observe that a given test particle undergoes a slightly stronger drag when moving through a distribution of field stars with relativistic velocity distribution. Vice versa, a purely classical treatment of a system where post-Newtonian (PN) corrections should be included, overestimates the effect of dynamical friction at low test particle velocity, regardless of the form of velocity distribution. Finally, a first-order PN dynamical friction covariant formulation is weaker its classical counterpart at small velocities, but much higher for large velocities over a broad range of mass ratios. [ABSTRACT FROM AUTHOR]

The Galactic nova rate is intimately linked to our understanding of its chemical enrichment and progenitor channels of Type Ia supernovae. Yet past estimates have varied by more than an order of magnitude (≈10–300 yr−1), owing to limitations in both discovery methods as well as assumptions regarding the Galactic dust distribution and extragalactic stellar populations. Recent estimates utilizing synoptic near-infrared surveys have begun to provide a glimpse of a consensus (≈25–50 yr−1); however, a consistent estimate remains lacking. Here, we present the first all-sky search for Galactic novae using 8 yr of data from the Near Earth Object WISE (NEOWISE) mid-infrared (MIR) survey. Operating at 3.4 and 4.6 µm where interstellar extinction is negligible, the 6-month cadence NEOWISE data set offers unique sensitivity to discover slowly evolving novae across the entire Galaxy. Using a novel image subtraction pipeline together with systematic selection criteria, we identify a sample of 49 rapidly evolving MIR outbursts as candidate Galactic novae. While 27 of these sources are known novae, the remaining are previously missed nova candidates discovered in this work. The unknown events are spatially clustered along the densest and most heavily obscured regions of the Galaxy where previous novae are severely underrepresented. We use simulations of the NEOWISE survey strategy, the pipeline detection efficiency, and our criteria to derive a Galactic nova rate of |$47.9^{+3.1}_{-8.3}$|  yr−1. The discovery of these exceptionally bright (yet overlooked) nova candidates confirms emerging suggestions that optical surveys have been highly incomplete in searches for Galactic novae, highlighting the potential for MIR searches in revealing the demographics of Galactic stellar outbursts. [ABSTRACT FROM AUTHOR]

We present a multizone galactic chemical evolution (GCE) model for the Milky Way that takes the most recently updated yields of major nucleosynthesis channels into account. It incorporates physical processes commonly found in previous GCE models like gas feedback from supernovae and star formation, the radial flow of gas in the disc, and the infall of fresh gas, along with stellar scattering processes like radial migration. We individually analyse the effect of different physical processes present in our model on the observed properties of the Galaxy. The radial flow of gas in the disc plays an important role in establishing the radial gradient for [Fe/H] in the low-[α/Fe] sequence. Our model with one episode of smooth gas infall and constant star formation efficiency is capable of reproducing the observed ([Fe/H], [α/Fe]) distribution of stars at different (R , | z |) positions in the Milky Way. Our results point to the rapid evolution of [α/Fe] after the onset of Type Ia supernovae and a high star formation rate during the formation of the high-[α/Fe] sequence as the origin of dual peaks in [α/Fe]. A secondary infall is unnecessary to reproduce the [α/Fe] gap and chemical spread in the disc in our model. We additionally compare the median age for various mono-abundance populations and the age–metallicity relation at different (R , | z |) positions from our fiducial model to observations. We discuss our results in relation to other related work in detail. [ABSTRACT FROM AUTHOR]

In this paper we analyse a sample of 46 barred galaxies of MaNGA. Our goal is to investigate the stellar kinematics of these galaxies and obtain their rotation curves. Additionally, we aim to derive the total stellar and dynamical masses, as well as the maximum rotation velocity, in order to examine their distributions and scaling relations. Using the Pipe3D dataproducts publicly available we obtained the rotation curves, which were fitted considering two components of an axisymmetric Miyamoto–Nagai gravitational potential. We found a wide range of the maximum rotation velocities (117–340  |${\rm km\, s^{-1}}$|⁠), with a mean value of 200  |${\rm km\, s^{-1}}$|⁠. In addition we found that the total stellar and dynamical masses are in the range of log(M star /M⊙) = 10.1−11.5, with a mean value of log(M star /M⊙) = 10.8, and log(M dyn /M⊙) = 10.4−12.0, with a mean value of log(M dyn /M⊙) = 11.1, respectively. We found a strong correlation between dynamical mass and maximum velocity, between maximum velocity and magnitude, and between stellar mass and maximum velocity. According to these results, barred galaxies exhibit similar behaviour to that of normal spiral galaxies with respect to these relations, as well as in terms of the distribution of their dynamical mass and maximum rotation velocity. However, we found that the distribution of stellar masses of barred galaxies is statistically different from other samples including non-barred galaxies. Finally, analysing the galaxies that show nuclear activity, we find no difference with the rotation curves of normal galaxies. [ABSTRACT FROM AUTHOR]

We perform high-resolution hydrodynamical simulations using the framework of MACER to investigate supermassive black hole (SMBH) feeding and feedback in a massive compact galaxy, which has a small effective radius but a large stellar mass, with a simulation duration of 10 Gyr. We compare the results with a reference galaxy with a similar stellar mass but a less concentrated stellar density distribution, as typically found in local elliptical galaxies. We find that about 10 per cent of the time, the compact galaxy develops multiphase gas within a few kpc, but the accretion flow through the inner boundary below the Bondi radius is always a single phase. The inflow rate in the compact galaxy is several times larger than in the reference galaxy, mainly due to the higher gas density caused by the more compact stellar distribution. Such a higher inflow rate results in stronger SMBH feeding and feedback and a larger fountain-like inflow-outflow structure. Compared to the reference galaxy, the star formation rate in the compact galaxy is roughly two orders of magnitude higher but is still low enough to be considered quiescent. Over the whole evolution period, the black hole mass grows by ∼50 per cent in the compact galaxy, much larger than the value of ∼ 3 per cent in the reference galaxy. [ABSTRACT FROM AUTHOR]

Classical T Tauri stars (TTS) are low-mass pre-main sequence stars with an active circumstellar environment. In this work, we present the identification and study of 260 classical TTS using LAMOST Data Release 6, among which 104 stars are newly identified. We distinguish classical TTS from giants and main-sequence dwarfs based on the log g values, and the presence of H α emission line and infrared excess that arises from the circumstellar accretion disk. We estimated the mass and age of 210 stars using the Gaia color–magnitude diagram. The age is from 0.1 to 20 Myr, where 90% of the stars have age <10 Myr and the mass ranges between 0.11 and 1.9 M ⊙ . From the measured H α equivalent widths, we homogeneously estimated the mass accretion rates for 172 stars, with most values ranging from 10 - 7 to 10 - 10 M ⊙ yr - 1 . The mass accretion rates are found to follow a power law distribution with the mass of the star, having a relation of the form M ˙ acc ∝ M ∗ 1.43 ± 0.26 , in agreement with previous studies. [ABSTRACT FROM AUTHOR]

Action-based dynamical modelling, using stars as dynamical tracers, is an excellent diagnostic to estimate the underlying axisymmetric matter distribution of the Milky Way. However, the Milky Way's bar causes non-axisymmetric resonance features in the stellar disc. Using RoadMapping (an action-based dynamical modelling framework to estimate the gravitational potential and the stellar distribution function), we systematically quantify the robustness of action-based modelling in the presence of a bar. We construct a set of test-particle simulations of barred galaxies (with varying bar properties), and apply RoadMapping to different survey volumes (with varying azimuthal position, size) drawn from these barred models. For realistic bar parameters, the global potential parameters are still recovered to within ∼1–17 per cent. However, with increasing bar strength, the best-fitting values of the parameters progressively deviate from their true values. This happens due to a combination of radial heating, radial migration, and resonance overlap phenomena in our bar models. Furthermore, the azimuthal location and the size of the survey volumes play important roles in the successful recovery of the parameters. Survey volumes along the bar major axis produce larger (relative) errors in the best-fitting parameter values. In addition, the potential parameters are better recovered for survey volumes with larger spatial coverage. As the Sun is located just ∼28°–33° behind the bar's major axis, an estimate for the bar-induced systematic bias – as provided by this study – is therefore crucial for future modelling attempts of the Milky Way. [ABSTRACT FROM AUTHOR]

We analyse the stellar abundances of massive galaxies (log  M */M⊙ > 10.5) at redshift, z  = 2, in the IllustrisTNG simulation with the goal of guiding the interpretation of current and future observations, particularly from JWST. We find that the effective size, R e, of galaxies strongly affects the abundance measurements: both [Mg/H] and [Fe/H] are anticorrelated with R e, while the relative abundance [Mg/Fe] slightly increases with R e. The α enhancement as tracked by [Mg/Fe] traces the formation time-scale of a galaxy weakly, and mostly depends on R e. Aperture effects are important: measuring the stellar abundances within 1 kpc instead of within R e can make a large difference. These results are all due to a nearly universal, steeply declining stellar abundance profile that does not scale with galaxy size – Small galaxies appear metal-rich because their stars live in the inner part of the profile where abundances are high. The slope of this profile is mostly set by the gas-phase abundance profile and not substantially modified by stellar age gradients. The gas-phase abundance profile, in turn, is determined by the strong radial dependence of the gas fraction and star-formation efficiency. We develop a simple model to describe the chemical enrichment, in which each radial bin of a galaxy is treated as an independent closed-box system. This model reproduces the gas-phase abundance profile of simulated galaxies, but not the detailed distribution of their stellar abundances, for which gas and/or metal transport are likely needed. [ABSTRACT FROM AUTHOR]

We continue our series of papers on phase-space distributions of stars in the Milky Way based on photometrically derived metallicities and Gaia astrometry, with a focus on the halo−disk interface in the local volume. To exploit various photometric databases, we develop a method of empirically calibrating synthetic stellar spectra based on a comparison with observations of stellar sequences and individual stars in the Sloan Digital Sky Survey, the SkyMapper Sky Survey, and the Pan-STARRS1 surveys, overcoming band-specific corrections employed in our previous work. In addition, photometric zero-point corrections are derived to provide an internally consistent photometric system with a spatially uniform metallicity zero-point. Using our phase-space diagrams, we find a remarkably narrow sequence in the rotational velocity (v ϕ ) versus metallicity ([Fe/H]) space for a sample of high proper-motion stars (>25 mas yr−1), which runs along Gaia Sausage/Enceladus (GSE) and the Splash substructures and is linked to the disk, spanning nearly 2 dex in [Fe/H]. Notably, a rapid increase of v ϕ from a nearly zero net rotation to ∼180 km s−1 in a narrow metallicity interval (−0.6 ≲ [Fe/H] ≲ −0.4) suggests that some of these stars emerged quickly on a short gas-depletion timescale. Through measurements of a scale height and length, we argue that these stars are distinct from those heated dynamically by mergers. This chain of high proper-motion stars provides additional support for recent discoveries suggesting that a starburst took place when the young Milky Way encountered the gas-rich GSE progenitor, which eventually led to the settling of metal-enriched gas onto the disk. [ABSTRACT FROM AUTHOR]