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Using a combination of Hubble Space Telescope (HST), JWST, and Atacama Large Millimeter/submillimeter Array (ALMA) data, we perform spatially resolved spectral energy distributions (SED) fitting of fourteen 4 < z < 6 ultraviolet (UV)-selected main-sequence galaxies targeted by the ALMA Large Program [C ii ] Resolved ISM in Star-forming Galaxies. We consistently model the emission from stars and dust in ∼0.5–1 kpc spatial bins to obtain maps of their physical properties. We find no offsets between the stellar masses (M *) and star formation rates (SFRs) derived from their global emission and those from adding up the values in our spatial bins, suggesting there is no bias of outshining by young stars on the derived global properties. We show that ALMA observations are important to derive robust parameter maps because they reduce the uncertainties in L dust (hence, AV and SFR). Using these maps, we explore the resolved star-forming main sequence for z ∼ 5 galaxies, finding that this relation persists in typical star-forming galaxies in the early Universe. We find less obscured star formation where the M * (and SFR) surface densities are highest, typically in the central regions, contrary to the global relation between these parameters. We speculate this could be caused by feedback driving gas and dust out of these regions. However, more observations of IR luminosities with ALMA are needed to verify this. Finally, we test empirical SFR prescriptions based on the UV+IR and [C ii ] line luminosity, finding they work well at the scales probed (approximately kiloparsec). Our work demonstrates the usefulness of joint HST-, JWST-, and ALMA-resolved SED modeling analyses at high redshift. [ABSTRACT FROM AUTHOR]

We present a catalog of stellar parameters (effective temperature T eff, surface gravity log g , age, and metallicity [Fe/H]) and elemental-abundance ratios ([C/Fe], [Mg/Fe], and [ α /Fe]) for some five million stars (4.5 million dwarfs and 0.5 million giant stars) in the Milky Way, based on stellar colors from the Javalambre Photometric Local Universe Survey (J-PLUS) DR3 and Gaia EDR3. These estimates are obtained through the construction of a large spectroscopic training set with parameters and abundances adjusted to uniform scales, and trained with a kernel principal component analysis. Owing to the seven narrow/medium-band filters employed by J-PLUS, we obtain precisions in the abundance estimates that are as good as or better than those derived from medium-resolution spectroscopy for stars covering a wide range of the parameter space: 0.10–0.20 dex for [Fe/H] and [C/Fe], and 0.05 dex for [Mg/Fe] and [ α /Fe]. Moreover, systematic errors due to the influence of molecular carbon bands on previous photometric-metallicity estimates (which only included two narrow/medium-band blue filters) have now been removed, resulting in photometric-metallicity estimates down to [Fe/H] ∼ −4.0, with typical uncertainties of 0.40 dex and 0.25 dex for dwarfs and giants, respectively. This large photometric sample should prove useful for the exploration of the assembly and chemical-evolution history of our Galaxy. [ABSTRACT FROM AUTHOR]

deepCR is a deep-learning-based cosmic-ray (CR) rejection framework originally presented by Zhang & Bloom. The original approach requires a dedicated training set that consists of multiple frames of the same fields, enabling automatic CR labeling through comparison with their median coadds. Here, we present a novel training approach that circumvents the need for a dedicated training set, but instead utilizes dark frames and the science images requiring CR removal themselves. During training, CRs present in dark frames are added to the science images, which the network is then trained to identify. In turn, the trained deepCR model can then be applied to identify CRs originally present in the science images. Using this approach, we present a new deepCR model trained on a diverse set of Hubble Space Telescope images taken from resolved galaxies in the Local Group, which is universally applicable across all WFC3/UVIS filters. We introduce a robust approach to determining the threshold for generating binary cosmic-ray masks from predictions from deepCR probability maps. When applied to the Panchromatic Hubble Andromeda Southern Treasury survey, our new deepCR model added ∼7% of good-quality stars that exhibit distinct features in their color–magnitude diagrams. [ABSTRACT FROM AUTHOR]

We report the discovery of Corvus A, a low-mass, gas-rich galaxy at a distance of approximately 3.5 Mpc, identified in DR10 of the Dark Energy Camera Legacy Imaging Survey during the initial phase of our ongoing SEmi-Automated Machine LEarning Search for Semi-resolved galaxies (SEAMLESS). Jansky Very Large Array observations of Corvus A detect H i line emission at a radial velocity of 523 ± 2 km s ^−1 . Magellan/Megacam imaging reveals an irregular and complex stellar population with both young and old stars. We detect UV emission in Neil Gehrels Swift observations, indicative of recent star formation. However, there are no signs of H ii regions in H α imaging from Steward Observatory’s Kuiper telescope. Based on the Megacam color–magnitude diagram we measure the distance to Corvus A via the tip of the red giant branch standard candle as 3.48 ± 0.24 Mpc. This makes Corvus A remarkably isolated, with no known galaxy within ∼1 Mpc. Based on this distance, we estimate the H i and stellar mass of Corvus A to be $\mathrm{log}{M}_{{\rm{H}}\,{\rm{I}}}/{M}_{\odot }=6.59$ and $\mathrm{log}{M}_{* }/{M}_{\odot }=6.0$ , respectively. Although there are some signs of rotation, the H i distribution of Corvus A appears to be close to face on, analogous to that of Leo T, and we therefore do not attempt to infer a dynamical mass from its H i line width. Higher-resolution synthesis imaging is required to confirm this morphology and to draw robust conclusions from its gas kinematics.

We study the H α equivalent width (EW(H α )) maps of 19 galaxies at 0.6 < z < 2.2 in the Hubble Ultra Deep Field using NIRISS slitless spectroscopy as part of the Next Generation Deep Extragalactic Exploratory Public Survey. Our galaxies mostly lie on the star formation main sequence with stellar masses between 10 ^9 and 10 ^11 M _⊙ , characterized as “typical” star-forming galaxies at these redshifts. Leveraging deep Hubble Space Telescope and JWST images, spanning 0.4–4.8 μ m, we perform spatially resolved fitting of the spectral energy distributions for these galaxies and construct specific star formation rate (sSFR) and stellar-mass-weighted age maps with a spatial resolution of ∼1 kpc. The pixel-to-pixel EW(H α ) increases with increasing sSFR and with decreasing age. The average trends are slightly different from the relations derived from integrated fluxes of galaxies from the literature, suggesting complex evolutionary trends within galaxies. We quantify the radial profiles of EW(H α ), sSFR, and age. The majority (84%) of galaxies show positive EW(H α ) gradients, in line with the inside-out quenching scenario. A few galaxies (16%) show inverse (and flat) EW(H α ) gradients, possibly due to merging or starbursts. We compare the distributions of EW(H α ) and sSFR to star formation history (SFH) models as a function of galactocentric radius. We argue that the central regions of galaxies have experienced at least one rapid star formation episode, which leads to the formation of the bulge, while their outer regions (e.g., disks) grow via more smoothly varying SFHs. These results demonstrate the ability to study resolved star formation in distant galaxies with JWST NIRISS.

The host galaxies of tidal disruption events (TDEs) have been shown to possess peculiar properties, including high central light concentrations, unusual star formation histories, and "green" colors. The ubiquity of these large-scale galaxy characteristics among TDE host populations suggests that they may serve to boost the TDE rate in such galaxies by influencing the nuclear stellar dynamics. We present the first population study of integral field spectroscopy for 13 TDE host galaxies across all spectral classes and X-ray brightnesses with the purpose of investigating their large-scale properties. We derive the black hole masses via stellar kinematics (i.e., the M – σ relation) and find masses in the range 5.0 ≲ log (M BH / M ⊙) ≲ 8.0 , with a distribution dominated by black holes with M BH ∼ 106 M ⊙. We find one object with M BH ≳ 108 M ⊙, above the "Hills mass", which if the disrupted star was of solar type, allows a lower limit of a ≳ 0.16 to be placed on its spin, lending further support to the proposed connection between featureless TDEs and jetted TDEs. We also explore the level of rotational support in the TDE hosts, quantified by (V / σ) e , a parameter that has been shown to correlate with the stellar age and may explain the peculiar host-galaxy preferences of TDEs. We find that the TDE hosts exhibit a broad range in (V / σ) e following a similar distribution as E + A galaxies, which have been shown to be overrepresented among TDE host populations. [ABSTRACT FROM AUTHOR]

We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]), α -element abundances ([Mg/Fe]), and stellar age, using a sample of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low- α disk, high- α disk, and total population independently. The low- α disk exhibits a negative radial metallicity gradient of −0.06 ± 0.001 dex kpc−1, which flattens with distance from the midplane. The high- α disk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]–[Fe/H] plane and in the [Mg/Fe]–age relation persist across the entire disk. The age estimates have typical uncertainties of ∼0.15 in log(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this sample. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy. [ABSTRACT FROM AUTHOR]

We combine an unprecedented MaNGA sample of over 3000 passive galaxies in the stellar mass range 109–1012 M ⊙ with the Sloan Digital Sky Survey group catalog by Tinker to quantify how central and satellite formation, quantified by radial profiles in stellar age, [Fe/H], and [Mg/Fe], depends on the stellar mass of the galaxy (M *) and the mass of the host halo (M h ). After controlling for M * and M h , the stacked spectra of centrals and satellites beyond the effective radius (r e ) show small, yet significant differences in multiple spectral features at the 1% level. According to spectral fitting with the code alf, a primary driver of these differences appears to be [Mg/Fe] variations, suggesting that stellar populations in the outskirts of satellites formed more rapidly than the outer populations of centrals. To probe the physical mechanisms that may be responsible for this signal, we examined how satellite stellar populations depend on M h . We find that satellites in high- M h halos show older stellar ages, lower [Fe/H], and higher [Mg/Fe] compared to satellites in low- M h halos, especially for M * = 109.5–1010.5 M ⊙. These signals lend support to environmentally driven processes that quench satellite galaxies, although variations in the merger histories of central and satellite galaxies also emerge as a viable explanation. [ABSTRACT FROM AUTHOR]

The PRObabilistic Value-added Bright Galaxy Survey (PROVABGS) catalog will provide measurements of galaxy properties, such as stellar mass (M *), star formation rate (SFR), stellar metallicity (Z), and stellar age (t age), for >10 million galaxies of the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey. Full posterior distributions of the galaxy properties will be inferred using state-of-the-art Bayesian spectral energy distribution (SED) modeling of DESI spectroscopy and Legacy Surveys photometry. In this work, we present the SED model, the neural emulator for the model, and the Bayesian inference framework of PROVABGS. Furthermore, we apply the PROVABGS SED modeling on realistic synthetic DESI spectra and photometry, constructed using the L-Galaxies semi-analytic model. We compare the inferred galaxy properties to the true values of the simulation using a hierarchical Bayesian framework to quantify accuracy and precision. Overall, we accurately infer the true M *, SFR, Z, and t age of the simulated galaxies. However, the priors on galaxy properties induced by the SED model have a significant impact on the posteriors, which we characterize in detail. This work also demonstrates that a joint analysis of spectra and photometry significantly improves the constraints on galaxy properties over photometry alone and is necessary to mitigate the impact of the priors. With the methodology presented and validated in this work, PROVABGS will maximize information extracted from DESI observations and extend current galaxy studies to new regimes and unlock cutting-edge probabilistic analyses. https://github.com/changhoonhahn/provabgs/ [ABSTRACT FROM AUTHOR]

Using a combination of Hubble Space Telescope (HST), JWST, and Atacama Large Millimeter/submillimeter Array (ALMA) data, we perform spatially resolved spectral energy distributions (SED) fitting of fourteen 4 < z < 6 ultraviolet (UV)-selected main-sequence galaxies targeted by the ALMA Large Program [C ii ] Resolved ISM in Star-forming Galaxies. We consistently model the emission from stars and dust in ∼0.5–1 kpc spatial bins to obtain maps of their physical properties. We find no offsets between the stellar masses ( M _* ) and star formation rates (SFRs) derived from their global emission and those from adding up the values in our spatial bins, suggesting there is no bias of outshining by young stars on the derived global properties. We show that ALMA observations are important to derive robust parameter maps because they reduce the uncertainties in L _dust (hence, A _V and SFR). Using these maps, we explore the resolved star-forming main sequence for z ∼ 5 galaxies, finding that this relation persists in typical star-forming galaxies in the early Universe. We find less obscured star formation where the M _* (and SFR) surface densities are highest, typically in the central regions, contrary to the global relation between these parameters. We speculate this could be caused by feedback driving gas and dust out of these regions. However, more observations of IR luminosities with ALMA are needed to verify this. Finally, we test empirical SFR prescriptions based on the UV+IR and [C ii ] line luminosity, finding they work well at the scales probed (approximately kiloparsec). Our work demonstrates the usefulness of joint HST-, JWST-, and ALMA-resolved SED modeling analyses at high redshift.

Boasting a 6.5 m mirror in space, JWST can increase by several times the number of supernovae (SNe) to which a redshift-independent distance has been measured with a precision distance indicator (e.g., tip of the red giant branch (TRGB) or Cepheids); the limited number of such SN calibrators currently dominates the uncertainty budget in distance ladder Hubble constant ( H _0 ) experiments. JWST/NIRCAM imaging of the Virgo Cluster galaxy NGC 4536 is used here to preview JWST program GO-1995, which aims to measure H _0 using three stellar distance indicators (Cepheids, TRGB, and J-branch asymptotic giant branch/carbon stars). Each population of distance indicator was here successfully detected—with sufficiently large number statistics, well-measured fluxes, and characteristic distributions consistent with ingoing expectations—so as to confirm that we can acquire distances from each method precise to about 0.05 mag (statistical uncertainty only). We leverage overlapping Hubble Space Telescope imaging to identify TRGB stars, crossmatch them with the JWST photometry, and present a preliminary constraint on the slope of the TRGB’s F115W versus (F115W – F444W) relation equal to −0.99 ± 0.16 mag mag ^−1 . This slope is consistent with prior slope measurements in the similar Two Micron All-Sky Survey J band, as well as with predictions from the BaSTI isochrone suite. We use the new TRGB slope estimate to flatten the 2D TRGB feature and measure a (blinded) TRGB distance relative to a set of fiducial TRGB colors, intended to represent the absolute fiducial calibrations expected from geometric anchors such as NGC 4258 and the Magellanic Clouds. In doing so, we empirically demonstrate that the TRGB can be used as a standardizable candle at the IR wavelengths accessible with JWST.

We present a catalog of stellar parameters (effective temperature T _eff , surface gravity $\mathrm{log}g$ , age, and metallicity [Fe/H]) and elemental-abundance ratios ([C/Fe], [Mg/Fe], and [ α /Fe]) for some five million stars (4.5 million dwarfs and 0.5 million giant stars) in the Milky Way, based on stellar colors from the Javalambre Photometric Local Universe Survey (J-PLUS) DR3 and Gaia EDR3. These estimates are obtained through the construction of a large spectroscopic training set with parameters and abundances adjusted to uniform scales, and trained with a kernel principal component analysis. Owing to the seven narrow/medium-band filters employed by J-PLUS, we obtain precisions in the abundance estimates that are as good as or better than those derived from medium-resolution spectroscopy for stars covering a wide range of the parameter space: 0.10–0.20 dex for [Fe/H] and [C/Fe], and 0.05 dex for [Mg/Fe] and [ α /Fe]. Moreover, systematic errors due to the influence of molecular carbon bands on previous photometric-metallicity estimates (which only included two narrow/medium-band blue filters) have now been removed, resulting in photometric-metallicity estimates down to [Fe/H] ∼ −4.0, with typical uncertainties of 0.40 dex and 0.25 dex for dwarfs and giants, respectively. This large photometric sample should prove useful for the exploration of the assembly and chemical-evolution history of our Galaxy.

Understanding the chemical enrichment of different elements is crucial to gaining a complete picture of galaxy chemical evolution. In this study, we present a new sample of 46 low-redshift, low-mass star-forming galaxies at M _* ∼ 10 ^8−10 M _⊙ along with two quiescent galaxies at M _* ∼ 10 ^8.8 M _⊙ observed with the Keck Cosmic Web Imager, aiming to investigate the chemical evolution of galaxies in the transition zone between Local Group satellites and massive field galaxies. We develop a novel method to simultaneously determine stellar abundances of iron and magnesium in star-forming galaxies. With the gas-phase oxygen abundance (O/H) _g measured using the strong-line method, we are able to make the first-ever apples-to-apples comparison of α elements in the stars and the interstellar medium. We find that the [Mg/H] _* –[O/H] _g relation is much tighter than the [Fe/H] _* –[O/H] _g relation, which can be explained by the similar production processes of α elements. Most galaxies in our sample exhibit higher [O/H] _g than [Fe/H] _* and [Mg/H] _* . In addition, we construct mass–metallicity relations (MZRs) measured as three different elements (Fe _* , Mg _* , O _g ). Compared to the gas O-MZR, the stellar Fe- and Mg-MZRs show larger scatter driven by variations in specific star formation rates (sSFR), with star-forming galaxies exhibiting higher sSFR and lower stellar abundances at fixed mass. The excess of [O/H] _g compared to stellar abundances as well as the anticorrelation between sSFR and stellar abundance suggests that galaxy quenching of intermediate-mass galaxies at M _* ∼ 10 ^8−10 M _⊙ is primarily driven by starvation.

In NGC 2992, a galaxy-scale ionized gas outflow driven by active galactic nuclei (AGNs) has long been recognized, yet its impact on the host galaxy has remained elusive. In this paper, we utilize data from the archival Very Large Telescope/MUSE to present a spatially resolved analysis of stellar populations in this galaxy. Two different stellar population templates are employed to fit the stellar continuum, allowing us to determine the light-weighted stellar age, metallicity, the fraction of the young stellar population (age

The stellar initial mass function (IMF) characterizes the mass distribution of newly formed stars in various cosmic environments, serving as a fundamental assumption in astrophysical research. Recent findings challenge the prevalent notion of a universal and static IMF, proposing instead that the IMF’s shape is contingent upon the star formation environment. In this study, we analyze the galaxy-wide variation in the IMF for low-mass stars in both dwarf and massive galaxies with diverse observational methods. Despite systematic discrepancies between different approaches, an IMF model with a metallicity-dependent slope for the low-mass stars aligns with the majority of observations, indicating a high degree of uniformity in the star formation processes across the Universe. We also emphasize the need for a more comprehensive understanding of the variation in the low-mass IMF, considering measurement biases and factors beyond metallicity.

The structure and evolution of the spiral arms of the Milky Way have long been an important yet controversial issue. The wide age range of OB-type stars, coupled with the large amount of high-precision astrometric data provided by Gaia DR3, presents us with an opportunity to explore this issue. After constructing overdensity maps and examining the variations of overdensities with Galactocentric distance along the Galactic azimuth, we compare the spiral structures traced by B3–B5, B6–B7, B8, and B9 stars with those of young O–B2 stars in the vicinity of the Sun. We find that as the ages of the OB tracer stars increase, the Perseus Arm traced by them gradually shifts toward the anti-Galactic center direction, and the pitch angle of the Carina Arm gradually decreases. These results will help us to understand better the evolutionary properties of nearby spiral arms.

We study 31 little red dots (LRD) detected by JADES/NIRCam and covered by the SMILES/MIRI survey, of which ∼70% are detected in the two bluest MIRI bands and 40% in redder MIRI filters. The median/quartiles redshifts are $z={6.9}_{5.9}^{7.7}$ (55% spectroscopic). The spectral slopes flatten in the rest-frame near-infrared, consistent with a 1.6 μ m stellar bump but bluer than direct pure emission from active galactic nuclei (AGN) tori. The apparent dominance of stellar emission at these wavelengths for many LRDs expedites stellar mass estimation: the median/quartiles are $\mathrm{log}{M}_{\star }/{M}_{\odot }={9.4}_{9.1}^{9.7}$ . The number density of LRDs is 10 ^−4.0±0.1 Mpc ^−3 , accounting for 14% ± 3% of the global population of galaxies with similar redshifts and masses. The rest-frame near-/mid-infrared (2–4 μ m) spectral slope reveals significant amounts of warm dust (bolometric attenuation ∼3–4 mag). Our spectral energy distribution modeling implies the presence of 10 mag. We find a wide variety in the nature of LRDs. However, the best-fitting models for many of them correspond to extremely intense and compact starburst galaxies with mass-weighted ages 5–10 Myr, very efficient in producing dust, with their global energy output dominated by the direct (in the flat rest-frame ultraviolet and optical spectral range) and dust-recycled emission from OB stars with some contribution from an obscured AGN (in the infrared).

We study 10 spectroscopically confirmed Ly α emitters (LAEs) at z ≈ 3.1 in the Ultra Deep Survey field, covered by the James Webb Space Telescope/NIRCam in the Public Release Imaging for Extragalactic Research program. All LAEs are detected in all NIRCam bands from F090W to F444W, corresponding to rest frame wavelengths of 2200 Å to 1.2 μ m. Based on morphological analysis of the F200W images, three out of the 10 targets are resolved into pair-like systems with separations of

We present stellar age determinations for 4661 red giant branch stars in the APO-K2 catalog, derived using mass estimates from K2 asteroseismology from the K2 Galactic Archaeology Program and elemental abundances from the Apache Point Galactic Evolution Experiment survey. Our sample includes 17 of the 19 fields observed by K2, making it one of the most comprehensive catalogs of accurate stellar ages across the Galaxy in terms of the wide range of populations spanned by its stars, enabling rigorous tests of Galactic chemical evolution models. Taking into account the selection functions of the K2 sample, the data appear to support the age−chemistry morphology of stellar populations predicted by both inside-out and late-burst scenarios. We also investigate trends in age versus stellar chemistry and Galactic position, which are consistent with previous findings. Comparisons against APOKASC-3 asteroseismic ages show agreement to within ∼3%. We also discuss offsets between our ages and spectroscopic ages. Finally, we note that ignoring the effects of α -enhancement on stellar opacity (either directly or with the Salaris metallicity correction) results in an ∼10% offset in age estimates for the most α -enhanced stars, which is an important consideration for continued tests of Galactic models with this and other asteroseismic age samples.

We report the discovery of eight optical counterparts of ALFALFA extragalactic objects from DECaLS, five of which are discovered for the first time. These objects were flagged as H i emission sources with no optical counterparts in SDSS before. Multiband data reveal their unusual physical properties. They are faint and blue ( g − r = −0.35 ∼ 0.55), with quite low surface brightness ( ${\mu }_{{\rm{g}},\mathrm{peak}}\,=\,24.88\sim 26.41\,\mathrm{mag}/{\mathrm{arcsec}}^{2}\;$ ), irregular morphologies, low stellar masses ( ${\mathrm{log}}_{10}\,({M}_{* }/{M}_{\odot })=5.27\sim 7.15$ ), low star formation rates (SFR = 0.21 ∼ 9.24 × 10 ^−3 M _⊙ yr ^−1 ), and remarkably high H i -to-stellar mass ratios ( ${\mathrm{log}}_{10}\,({M}_{\mathrm{HI}}/{M}_{* })=1.72\sim 3.22$ , except AGC 215415). They deviate from the scaling relations between H i and optical properties defined by the ALFALFA sample and the baryonic Tully–Fisher relation. They agree well with the main sequence of star-forming galaxies but exhibit low star-forming efficiency. Based on their physical properties and environments, we speculate that six of these objects may have originated from tidal processes, while the remaining two appear to have isolated origins. They may have had a relatively calm evolutionary history and only begun to form stars recently.

We combine photometric data from GALEX GR6+7 All-Sky Imaging Survey and Gaia Early Data Release 3 with stellar parameters from the SAGA and PASTEL catalogs to construct high-quality training samples for dwarfs (0.4 < BP − RP < 1.6) and giants (0.6 < BP − RP < 1.6). We apply careful reddening corrections using empirical temperature- and extinction-dependent extinction coefficients. Using the two samples, we establish a relationship between stellar loci (near-ultraviolet (NUV)−BP versus BP − RP colors), metallicity, and M _G . For a given BP − RP color, a 1 dex change in [Fe/H] corresponds to an approximately 1 magnitude change in NUV − BP color for solar-type stars. These relationships are employed to estimate metallicities based on NUV − BP, BP − RP, and M _G . Thanks to the strong metallicity dependence in the GALEX NUV band, our models enable a typical photometric-metallicity precision of approximately σ _[Fe/H] = 0.11 dex for dwarfs and σ _[Fe/H] = 0.17 dex for giants, with an effective metallicity range extending down to [Fe/H] = −3.0 for dwarfs and [Fe/H] = −4.0 for giants. We also find that the NUV-band-based photometric-metallicity estimate is not as strongly affected by carbon enhancement as previous photometric techniques. With the GALEX and Gaia data, we have estimated metallicities for about 5 million stars across almost the entire sky, including approximately 4.5 million dwarfs and 0.5 million giants. This work demonstrates the potential of the NUV band for estimating photometric metallicities, and sets the groundwork for utilizing the NUV data from space telescopes such as the upcoming Chinese Space Station Telescope.

Phylogenetic methods have long been used in biology and more recently have been extended to other fields—for example, linguistics and technology—to study evolutionary histories. Galaxies also have an evolutionary history and fall within this broad phylogenetic framework. Under the hypothesis that chemical abundances can be used as a proxy for the interstellar medium’s DNA, phylogenetic methods allow us to reconstruct hierarchical similarities and differences among stars—essentially, a tree of evolutionary relationships and thus history. In this work, we apply phylogenetic methods to a simulated disk galaxy obtained with a chemodynamical code to test the approach. We found that at least 100 stellar particles are required to reliably portray the evolutionary history of a selected stellar population in this simulation, and that the overall evolutionary history is reliably preserved when the typical uncertainties in the chemical abundances are smaller than 0.08 dex. The results show that the shapes of the trees are strongly affected by the age–metallicity relation, as well as the star formation history of the galaxy. We found that regions with low star formation rates produce shorter trees than regions with high star formation rates. Our analysis demonstrates that phylogenetic methods can shed light on the process of galaxy evolution.

Stellar counterrotation in disk galaxies directly relates to the complex phenomenon of the disk mass assembly believed to be driven by external processes, such as accretion and mergers. The study of such systems makes it possible to reveal the source of external accretion and establish the details of this process. In this paper, we investigate the galaxy PGC 66551 (MaNGA ID 1-179561), which hosts two large-scale counterrotating (CR) stellar disks identified in the Sloan Digital Sky Survey MaNGA data and then confirmed using deep follow-up spectroscopy with the 10 m Southern African Large Telescope. We measured the properties of ionized gas and stellar populations of both CR disks in PGC 66551. We found that the CR disk is compact, contains young stars with subsolar metallicity, and has a stellar mass of 5 × 10 ^9 M _⊙ , which amounts to ≈20% of the galaxy’s total. Surprisingly, the main 8 Gyr old disk has a significantly lower metallicity of −0.8 dex than other CR galaxies. We developed a simple analytic model of the history of the metal enrichment, which we applied to PGC 66551 and constrained the parameters of the galactic outflow wind, and estimated the metallicity of the infalling gas that formed the CR disk to be −0.9... −0.5 dex. Our interpretation prefers a merger with a gas-rich satellite over cold accretion from a cosmic filament as a source of gas, which then formed the CR disk in PGC 66551.

We present individual star formation histories (SFHs) of ∼3000 massive galaxies (log( M _* / M _⊙ ) > 10.5) from the Large Early Galaxy Astrophysics Census spectroscopic survey at a lookback time of ∼7 billion yr and quantify the population trends leveraging 20 hr deep-integrated spectra of these ∼1800 star-forming and ∼1200 quiescent galaxies at 0.6 < z < 1.0. Essentially all galaxies at this epoch contain stars of age

We report the serendipitous discovery of VVV-WIT-12, an unusual variable source that seems to induce variability in its surrounding nebula. The source belongs to the rare objects that we call WITs (short for What Is This?) discovered within the VISTA Variables in the Vía Láctea (VVV) survey. VVV-WIT-12 was discovered during a pilot search for light echoes from distant supernovae in the Milky Way using the near-IR images of the VVV survey. This source has an extremely red spectral energy distribution, consistent with a very reddened ( A _V ∼ 100 mag) long-period variable star ( P ∼ 1525 days). Furthermore, it is enshrouded in a nebula that changes brightness and color with time, apparently in sync with the central source variations. The near-IR light curve and complementary follow-up spectroscopy observations are consistent with a variable young stellar object illuminating its surrounding nebula. In this case the source periodic variation along the cycles produces an unprecedented light echo in the different regions of the nebula.

We report the discovery of Pavo, a faint ( M _V = −10.0), star-forming, irregular, and extremely isolated dwarf galaxy at D ≈ 2 Mpc. Pavo was identified in Dark Energy Camera Legacy Survey imaging via a novel approach that combines low surface brightness galaxy search algorithms and machine-learning candidate classifications. Follow-up imaging with the Inamori-Magellan Areal Camera and Spectrograph on the 6.5 m Magellan Baade telescope revealed a color–magnitude diagram (CMD) with an old stellar population, in addition to the young population that dominates the integrated light, and a tip of the red giant branch distance estimate of ${1.99}_{-0.22}^{+0.20}$ Mpc. The blue population of stars in the CMD is consistent with the youngest stars having formed no later than 150 Myr ago. We also detected no H α emission with SOAR telescope imaging, suggesting that we may be witnessing a temporary low in Pavo’s star formation. We estimate the total stellar mass of Pavo to be $\mathrm{log}{M}_{* }/{M}_{\odot }=5.6\pm 0.2$ and measure an upper limit on its H i gas mass of 1.0 × 10 ^6 M _⊙ based on the HIPASS survey. Given these properties, Pavo’s closest analog is Leo P ( D = 1.6 Mpc), previously the only known isolated, star-forming, Local Volume dwarf galaxy in this mass range. However, Pavo appears to be even more isolated, with no other known galaxy residing within over 600 kpc. As surveys and search techniques continue to improve, we anticipate an entire population of analogous objects being detected just outside the Local Group.

We present the first results on the spatial distribution of dust attenuation at 1.0 < z < 2.4 traced by the Balmer decrement, H α /H β , in emission-line galaxies using deep JWST NIRISS slitless spectroscopy from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). H α and H β emission-line maps of emission-line galaxies are extracted and stacked in bins of stellar mass for two grism redshift bins, 1.0 < z _grism < 1.7 and 1.7 < z _grism < 2.4. Surface brightness profiles for the Balmer decrement are measured and radial profiles of the dust attenuation toward H α , A _H _α , are derived. In both redshift bins, the integrated Balmer decrement increases with stellar mass. Lower-mass (7.6 ≤ Log( M _* / M _⊙ ) < 10.0) galaxies have centrally concentrated, negative dust attenuation profiles whereas higher-mass galaxies (10.0 ≤ Log( M _* / M _⊙ ) < 11.1) have flat dust attenuation profiles. The total dust obscuration is mild, with on average 0.07 ± 0.07 and 0.14 ± 0.07 mag in the low- and high-redshift bins respectively. We model the typical light profiles of star-forming galaxies at these redshifts and stellar masses with GALFIT and apply both uniform and radially varying dust attenuation corrections based on our integrated Balmer decrements and radial dust attenuation profiles. If the H α star formation rates (SFRs) of these galaxies were measured after slit-loss corrections assuming uniform dust attenuation with typical JWST NIRSpec slit spectroscopy (0.″2 × 0.″5 shutters), the total SFR will be overestimated by 6% ± 21% and 26% ± 9% at 1.0 ≤ z < 1.7 and 1.7 ≤ z < 2.4 respectively.

Through adaptive optics (AO) imaging with the SOUL+LUCI instrument at the Large Binocular Telescope we were able to resolve, for the first time, individual stars in the gas-rich galaxy DDO68 C. This system was already suggested to be interacting with the extremely metal-poor dwarf DDO68, but its nature has remained elusive so far because of the presence of a bright foreground star close to its line of sight that hampers a detailed study of its stellar population and distance. In our study, we turned this interloper star into an opportunity to have a deeper insight on DDO68 C, using it as a guide star for the AO correction. Although the new data do not allow for a direct distance measurement through the red giant branch tip method, the combined analysis of the resolved-star color–magnitude diagram, of archival GALEX far-UV and near-UV photometry, and of H α data provides a self-consistent picture in which DDO68 C is at the same ∼13 Mpc distance as its candidate companion DDO68. These results indicate that DDO68 is a unique case of a low-mass dwarf, less massive than the Magellanic Clouds, interacting with three satellites (DDO68 C and two previously confirmed accreting systems), providing useful constraints on cosmological models and a potential explanation for its anomalous extremely low metallicity.

We have obtained high-quality spectra of blue supergiant candidates in the dwarf irregular galaxy Leo A with the Low Resolution Imaging Spectrometer at the Keck I telescope. From the quantitative analysis of seven B8–A0 stars, we derive a mean metallicity [ Z ] = −1.35 ± 0.08, in excellent agreement with the gas-phase chemical abundance. From the stellar parameters and the flux-weighted gravity–luminosity relation (FGLR), we derive a spectroscopic distance modulus m − M = 24.77 ± 0.11 mag, significantly larger (∼0.4 mag) than the value indicated by RR Lyrae and other stellar indicators. We explain the bulk of this discrepancy with blue loop stellar evolution at very low metallicity and show that the combination of metallicity effects and blue loop evolution amounts, in the case of Leo A, to an ∼0.35 mag offset of the FGLR to fainter bolometric luminosities. We identify one outlier of low bolometric magnitude as a post-AGB star. Its metallicity is consistent with that of the young population, confirming the slow chemical enrichment of Leo A.

The forthcoming Chinese Space Station Telescope (CSST) wide-field multiband imaging survey will produce seven-band photometric spectral energy distributions (SEDs) for billions of galaxies. The effective extraction of astronomical information from these massive data sets of SEDs relies on the techniques of SED synthesis (or modeling) and SED analysis (or fitting). We evaluate the performance of the latest version of the BayeSED code combined with SED models with increasing complexity for simultaneously determining the photometric redshifts and stellar population parameters of galaxies in this survey. By using an empirical statistics–based mock galaxy sample without SED modeling errors, we show that the random observational errors in photometries are more important sources of errors than the parameter degeneracies and Bayesian analysis method and tool. By using a Horizon-AGN hydrodynamical simulation–based mock galaxy sample with SED modeling errors about the star formation histories (SFHs) and dust attenuation laws (DALs), the simple typical assumptions lead to significantly worse parameter estimation with CSST photometries only. SED models with more flexible (or complicated) forms of SFH/DAL do not necessarily lead to better estimation of redshift and stellar population parameters. We discuss the selection of the best SED model by means of Bayesian model comparison in different surveys. Our results reveal that Bayesian model comparison with Bayesian evidence may favor SED models with different complexities when using photometries from different surveys. Meanwhile, the SED model with the largest Bayesian evidence tends to give the best performance of parameter estimation, which is clearer for photometries with higher discriminative power.

The host galaxies of tidal disruption events (TDEs) have been shown to possess peculiar properties, including high central light concentrations, unusual star formation histories, and “green” colors. The ubiquity of these large-scale galaxy characteristics among TDE host populations suggests that they may serve to boost the TDE rate in such galaxies by influencing the nuclear stellar dynamics. We present the first population study of integral field spectroscopy for 13 TDE host galaxies across all spectral classes and X-ray brightnesses with the purpose of investigating their large-scale properties. We derive the black hole masses via stellar kinematics (i.e., the M – σ relation) and find masses in the range $5.0\lesssim \mathrm{log}({M}_{\mathrm{BH}}/{M}_{\odot })\lesssim 8.0$ , with a distribution dominated by black holes with M _BH ∼ 10 ^6 M _⊙ . We find one object with M _BH ≳ 10 ^8 M _⊙ , above the “Hills mass”, which if the disrupted star was of solar type, allows a lower limit of a ≳ 0.16 to be placed on its spin, lending further support to the proposed connection between featureless TDEs and jetted TDEs. We also explore the level of rotational support in the TDE hosts, quantified by ( V / σ ) _e , a parameter that has been shown to correlate with the stellar age and may explain the peculiar host-galaxy preferences of TDEs. We find that the TDE hosts exhibit a broad range in ( V / σ ) _e following a similar distribution as E + A galaxies, which have been shown to be overrepresented among TDE host populations.

We present a comprehensive multiwavelength study of five post-starburst galaxies with M _* > 10 ^11 M _⊙ at z ∼ 0.7, examining their stars, gas, and current and past star formation activities. Using optical images from the Subaru Telescope and Hubble Space Telescope, we observe a high incidence of companion galaxies and low surface brightness tidal features, indicating that quenching is closely related to interactions between galaxies. From optical spectra provided by the LEGA-C survey, we model the stellar continuum to derive the star formation histories and show the stellar masses of progenitors ranging from 2 × 10 ^9 M _⊙ to 10 ^11 M _⊙ , undergoing a burst of star formation several hundred million years prior to observation, with a decay timescale of ∼100 Myr. Our Atacama Large Millimeter/submillimeter Array observations detect CO(2-1) emission in four galaxies, with the molecular gas spreading over up to >1″, or ∼10 kpc, with a mass of up to ∼2 × 10 ^10 M _⊙ . However, star-forming regions are unresolved by either the slit spectra or 3 GHz continuum observed by the Very Large Array. Comparisons between the star formation rates (SFRs) and gas masses, and the sizes of CO emission and star-forming regions suggest a low star-forming efficiency. We show that the SFRs derived from IR and radio luminosities with commonly used calibrations tend to overestimate the true values because of the prodigious amount of radiation from old stars and the contribution from active galactic nuclei (AGNs), as the optical spectra reveal weak AGN-driven outflows.

We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]), α -element abundances ([Mg/Fe]), and stellar age, using a sample of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low- α disk, high- α disk, and total population independently. The low- α disk exhibits a negative radial metallicity gradient of −0.06 ± 0.001 dex kpc ^−1 , which flattens with distance from the midplane. The high- α disk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]–[Fe/H] plane and in the [Mg/Fe]–age relation persist across the entire disk. The age estimates have typical uncertainties of ∼0.15 in log(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this sample. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy.

In this empirical work, we aim to quantify the systematic uncertainties in stellar-mass ( M _⋆ ) estimates made from spectral energy distribution (SED) fitting through stellar population synthesis (SPS) for galaxies in the local Universe by using the dynamical mass ( M _dyn ) estimator as an SED-independent check on stellar mass. We first construct a statistical model of the high-dimensional space of galaxy properties; including size ( R _e ), velocity dispersion ( σ _e ), surface brightness ( I _e ), mass-to-light ratio ( M _⋆ / L ), rest-frame color, Sérsic index ( n ), and dynamical mass ( M _dyn ), and accounting for selection effects and covariant errors. We disentangle the correlations among galaxy properties and find that the variation in M _⋆ / M _dyn is driven by σ _e , Sérsic index and color. We use these parameters to calibrate an SED-independent M _⋆ estimator, ${\hat{M}}_{\star }$ . We find the random scatter of the relation ${M}_{\star }-{\hat{M}}_{\star }$ to be 0.108 dex and 0.147 dex for quiescent and star-forming galaxies, respectively. Finally, we inspect the residuals as a function of SPS parameters (dust, age, metallicity, and star formation rate) and spectral indices (H α , H δ , and D _n 4000). For quiescent galaxies, ∼65% of the scatter can be explained by the uncertainty in SPS parameters, with dust and age being the largest sources of uncertainty. For star-forming galaxies, while age and metallicity are the leading factors, SPS parameters account for only ∼13% of the scatter. These results leave us with remaining unmodelled scatters of 0.055 dex and 0.122 dex for quiescent and star-forming galaxies, respectively. This can be interpreted as a conservative limit on the precision in M _⋆ that can be achieved via simple SPS modeling.

We present a study of the structural properties and metallicity distribution of the nearby peculiar galaxy NGC 3077. Using data from our survey of the M81 Group with the Hyper Suprime-Cam on board the Subaru Telescope, we construct deep color–magnitude diagrams that are used to probe the old red giant branch (RGB) population of NGC 3077. We map these stars out to and beyond the nominal tidal radius, which allows us to derive the structural properties and stellar content of the peripheral regions. We show that NGC 3077 has an extended stellar halo and pronounced “S-shaped” tidal tails that diverge from the radial profile of the inner region. The average metallicity of the old population in NGC 3077 is estimated from individual RGBs to be [M/H] = −0.98 ± 0.26, which decreases with the distance from the galaxy center as [M/H] = −0.17 dex ${R}_{h}^{-1}$ . The metallicity of the S-shaped structure is similar to that of the regions lying at r ∼ 4 × R _h ( ∼ 30 kpc), indicating that the stellar constituents of the tidal tails have come from the outer envelope of NGC 3077. These results suggest that this peculiar galaxy was probably a rather normal dwarf elliptical galaxy before the tidal interaction with M81 and M82. We also examine the evidence in our data set for the six recently reported ultrafaint dwarf candidates around NGC 3077. We recover a spatial overdensity of sources coinciding with only one of these.

We present elemental abundance patterns (C, N, Mg, Si, Ca, Ti, V, Cr, Fe, Co, and Ni) for a population of 135 massive quiescent galaxies at z ∼ 0.7 with ultra-deep rest-frame optical spectroscopy drawn from the LEGA-C survey. We derive average ages and elemental abundances in four bins of stellar velocity dispersion ( σ _v ) ranging from 150–250 km s ^−1 using a full-spectrum hierarchical Bayesian model. The resulting elemental abundance measurements are precise to 0.05 dex. The majority of elements, as well as the total metallicity and stellar age, show a positive correlation with σ _v . Thus, the highest dispersion galaxies formed the earliest and are the most metal-rich. We find only mild or nonsignificant trends between [X/Fe] and σ _v , suggesting that the average star formation timescale does not strongly depend on velocity dispersion. To first order, the abundance patterns of the z ∼ 0.7 quiescent galaxies are strikingly similar to those at z ∼ 0. However, at the lowest-velocity dispersions, the z ∼ 0.7 galaxies have slightly enhanced N, Mg, Ti, and Ni abundance ratios and earlier formation redshifts than their z ∼ 0 counterparts. Thus, while the higher-mass quiescent galaxy population shows little evolution, the low-mass quiescent galaxies population has grown significantly over the past 6 Gyr. Finally, the abundance patterns of both z ∼ 0 and z ∼ 0.7 quiescent galaxies differ considerably from theoretical prediction based on a chemical evolution model, indicating that our understanding of the enrichment histories of these galaxies is still very limited.

We derive and publish data-driven estimates of stellar metallicity [M/H] for ∼175 million stars with low-resolution XP spectra published in Gaia DR3. The [M/H] values, along with T _eff and $\mathrm{log}g$ , are derived using the XGBoost algorithm, trained on stellar parameters from APOGEE, augmented by a set of very-metal-poor stars. XGBoost draws on a number of data features: the full set of XP spectral coefficients, narrowband fluxes derived from XP spectra, and broadband magnitudes. In particular, we include CatWISE magnitudes, as they reduce the degeneracy of T _eff and dust reddening. We also include the parallax as a data feature, which helps constrain $\mathrm{log}g$ and [M/H]. The resulting mean stellar parameter precision is 0.1 dex in [M/H], 50 K in T _eff , and 0.08 dex in $\mathrm{log}g$ . This all-sky [M/H] sample is substantially larger than published samples of comparable fidelity across −3 ≲ [M/H] ≲ +0.5. Additionally, we provide a catalog of over 17 million bright ( G < 16) red giants whose [M/H] values are vetted to be precise and pure. We present all-sky maps of the Milky Way in different [M/H] regimes that illustrate the purity of the data set, and demonstrate the power of this unprecedented sample to reveal the Milky Way’s structure from its heart to its disk.

We present the mid-infrared (MIR) morphologies for 64 star-forming galaxies (SFGs) at 0.2 < z < 2.5 with stellar mass M _* > 10 ^9 M _⊙ using James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) observations from the Cosmic Evolution Early Release Science survey. The MIRI bands span the MIR (7.7–21 μ m), enabling us to measure the effective radii ( R _eff ) and Sérsic indexes of these SFGs at rest-frame 6.2 and 7.7 μ m, which contains strong emission from Polycyclic aromatic hydrocarbon (PAH) features, a well-established tracer of star formation in galaxies. We define a “PAH band” as the MIRI bandpass that contains these features at the redshift of the galaxy. We then compare the galaxy morphologies in the PAH bands to those in the rest-frame near-ultraviolet (NUV) using Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/F435W or ACS/F606W and optical/near-IR using HST WFC3/F160W imaging from UVCANDELS and CANDELS. The R _eff of galaxies in the PAH band are slightly smaller (∼10%) than those in F160W for galaxies with M _* ≳ 10 ^9.5 M _⊙ at z ≤ 1.2, but the PAH band and F160W have similar fractions of light within 1 kpc. In contrast, the R _eff of galaxies in the NUV band are larger, with lower fractions of light within 1 kpc compared to F160W for galaxies at z ≤ 1.2. Using the MIRI data to estimate the SFR _IR surface density, we find that the correlation between the SFR _IR surface density and stellar mass has a steeper slope than that of the SFR _UV surface density and stellar mass, suggesting more massive galaxies having increasing amounts of obscured fraction of star formation in their inner regions. This paper demonstrates how the high-angular resolution data from JWST/MIRI can reveal new information about the morphology of obscured star formation.

We investigate the mass–metallicity relationship of star-forming galaxies by analyzing the absorption line spectra of ∼200,000 galaxies in the Sloan Digital Sky Survey. The galaxy spectra are stacked in bins of stellar mass, and a population synthesis technique is applied yielding the metallicities, ages, and star formation history of the young and old stellar population together with interstellar reddening and extinction. We adopt different lengths of the initial starbursts and different initial mass functions for the calculation of model spectra of the single stellar populations contributing to the total integrated spectrum. We also allow for deviations of the ratio of extinction to reddening R _V from 3.1 and determine the value from the spectral fit. We find that burst length and R _V have a significant influence on the determination of metallicities, whereas the effect of the initial mass function is small. The R _V values are larger than 3.1. The metallicities of the young stellar population agree with extragalactic spectroscopic studies of individual massive supergiant stars and are significantly higher than those of the older stellar population. This confirms galaxy evolution models where metallicity depends on the ratio of gas to stellar mass and where this ratio decreases with time. Star formation history is found to depend on galaxy stellar mass. Massive galaxies are dominated by stars formed at early times.

We present stellar parameters and abundances of 13 elements for 18 very metal-poor (VMP; [Fe/H] < –2.0) stars, selected as extremely metal-poor (EMP; [Fe/H] < –3.0) candidates from the Sloan Digital Sky Survey and Large sky Area Multi-Object Fiber Spectroscopic Telescope survey. High-resolution spectroscopic observations were performed using GEMINI-N/GRACES. We find 10 EMP stars among our candidates, and we newly identify three carbon-enhanced metal-poor stars with [Ba/Fe] < 0. Although chemical abundances of our VMP/EMP stars generally follow the overall trend of other Galactic halo stars, there are a few exceptions. One Na-rich star ([Na/Fe] = +1.14) with low [Mg/Fe] suggests a possible chemical connection with second-generation stars in a globular cluster. The progenitor of an extremely Na-poor star ([Na/Fe] = –1.02) with high K- and Ni-abundance ratios may have undergone a distinct nucleosynthesis episode, associated with core-collapse supernovae (SNe) having a high explosion energy. We have also found a Mg-rich star ([Mg/Fe] = +0.73) with slightly enhanced Na and extremely low [Ba/Fe], indicating that its origin is not associated with neutron-capture events. On the other hand, the origin of the lowest Mg abundance ([Mg/Fe] = –0.61) star could be explained by accretion from a dwarf galaxy, or formation in a gas cloud largely polluted by SNe Ia. We have also explored the progenitor masses of our EMP stars by comparing their chemical-abundance patterns with those predicted by Population III SNe models, and find a mass range of 10–26 M _⊙ , suggesting that such stars were primarily responsible for the chemical enrichment of the early Milky Way.

The HectoMAP survey provides a complete, mass-limited sample of 30,231 quiescent galaxies with i -band Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) imaging that spans the redshift range 0.2 < z < 0.6. We combine half-light radii based on HSC SSP imaging with redshifts and D _n 4000 to explore the size–mass relation, ${R}_{e}=A\times {M}_{* }^{\alpha }$ , and its evolution for the entire HectoMAP quiescent population and for two subsets of the data. Newcomers with 1.5 < D _n 4000 < 1.6 at each redshift show a steeper increase in A as the universe ages than the population that descends from galaxies that are already quiescent at the survey limit, z ∼ 0.6 (the resident population). In broad agreement with previous studies, evolution in the size–mass relation both for the entire HectoMAP sample and for the resident population (but not for the newcomers alone) is consistent with minor merger driven growth. For the resident population, the evolution in the size–mass relation is independent of the population age at z ∼ 0.6. The contrast between the sample of newcomers and the resident population provides insight into the role of commonly termed “progenitor bias” on the evolution of the size–mass relation.

Observations with the Hubble Space Telescope unexpectedly revealed that the dwarf galaxy ESO 006–001 is a near neighbor to the Local Group at a distance of 2.70 ± 0.11 Mpc. The stellar population in the galaxy is well resolved into individual stars to a limit of M _I ∼ − 0.5 mag. The dominant population is older than 12 Gyr yet displays a significant range in metallicity of −2 < [Fe/H] < − 1, as evidenced by a red giant branch with substantial width. Superimposed on the dominant population are stars on the main sequence with ages less than 100 Myr and helium burning blue loop stars with ages of several hundred Myr. ESO 006–001 is an example of a transition dwarf; a galaxy dominated by old stars but one that has experienced limited recent star formation in a swath near the center. No H i gas is detected at the location of the optical galaxy in spite of the evidence for young stars. Intriguingly, an H i cloud with a similar redshift is detected 9 kpc away in projection. Otherwise, ESO 006–001 is a galaxy in isolation with its nearest known neighbor IC 3104, itself a dwarf, at a distance of ∼500 kpc.

We investigate the stellar and ionized gas kinematics, and stellar populations of NGC 3182 galaxy using integral field spectrograph data from the Calar Alto Legacy Integral Field Area survey. We try to clarify the nature of the ring structure in NGC 3182. We find a negative stellar age gradient out to the ring, while [ α /Fe] considerably enhanced in the ring. The stellar metallicity shows a smooth negative gradient. From the line-ratio diagnostic diagrams, we confirm that NGC 3182 is a Seyfert galaxy from emission-line flux ratio, while the gas in the inner ring is ionized mostly by young stars. However, any obvious feature of outflows is not found in its gas kinematics. In the ring, star formation seems to have recently occurred and the gas metallicity is slightly enhanced compared to the center. From our results, we conclude that star formation has occurred in the circumnuclear region within a short period and this may result from a positive feedback by active galactic nucleus radiation pressure.

Stellar kinematics and metallicity are key to exploring formation scenarios for galactic disks and halos. In this work, we characterized the relationship between kinematics and photometric metallicity along the line of sight to M31's disk. We combined optical Hubble Space Telescope/Advanced Camera for Surveys photometry, from the Panchromatic Hubble Andromeda Treasury survey, with Keck/DEIMOS spectra, from the Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo survey. The resulting sample of 3512 individual red giant branch stars spans 4–19 projected kpc, making it a useful probe of both the disk and inner halo. We separated these stars into disk and halo populations, by modeling the line-of-sight velocity distributions as a function of position across the disk region, where ∼73% stars have a high likelihood of belonging to the disk and ∼14% to the halo. Although stellar halos are typically thought to be metal-poor, the kinematically identified halo contains a significant population of stars (∼29%) with disk-like metallicity ([Fe/H] _phot ∼ −0.10). This metal-rich halo population lags the gaseous disk to a similar extent as the rest of the halo, indicating that it does not correspond to a canonical thick disk. Its properties are inconsistent with those of tidal debris originating from the Giant Stellar Stream merger event. Moreover, the halo is chemically distinct from the phase-mixed component previously identified along the minor axis (i.e., away from the disk), implying contributions from different formation channels. These metal-rich halo stars provide direct chemodynamical evidence in favor of the previously suggested “kicked-up” disk population in M31's inner stellar halo.

We present a forward-modeling framework for estimating galaxy redshift distributions from photometric surveys. Our forward model is composed of: a detailed population model describing the intrinsic distribution of the physical characteristics of galaxies, encoding galaxy evolution physics; a stellar population synthesis model connecting the physical properties of galaxies to their photometry; a data model characterizing the observation and calibration processes for a given survey; and explicit treatment of selection cuts, both into the main analysis sample and for the subsequent sorting into tomographic redshift bins. This approach has the appeal that it does not rely on spectroscopic calibration data, provides explicit control over modeling assumptions and builds a direct bridge between photo- z inference and galaxy evolution physics. In addition to redshift distributions, forward modeling provides a framework for drawing robust inferences about the statistical properties of the galaxy population more generally. We demonstrate the utility of forward modeling by estimating the redshift distributions for the Galaxy And Mass Assembly (GAMA) survey and the Vimos VLT Deep Survey (VVDS), validating against their spectroscopic redshifts. Our baseline model is able to predict tomographic redshift distributions for GAMA and VVDS with respective biases of Δ z ≲ 0.003 and Δ z ≃ 0.01 on the mean redshift—comfortably accurate enough for Stage III cosmological surveys—without any hyperparameter tuning (i.e., prior to doing any fitting to those data). We anticipate that with additional hyperparameter fitting and modeling improvements, forward modeling will provide a path to accurate redshift distribution inference for Stage IV surveys.

We study the impact of galaxy mergers on stellar population profiles/gradients of early-type galaxies (ETGs) using ETGs at z < 0.055 in the Stripe 82 region of the Sloan Digital Sky Survey and MaNGA integral field unit spectroscopic data. Tidal features around ETGs, which are detected from deep coadded images, are regarded as direct observational evidence for recent mergers. We find that ETGs with tidal features have less negative metallicity gradients and more positive age gradients than ETGs without tidal features at M _star ≳ 10 ^10.6 M _⊙ . Moreover, when integrating all the resolved stellar populations, ETGs with tidal features have lower metallicities by ∼0.07 dex and younger ages by ∼1–2 Gyr than ETGs without tidal features. Analyzing star formation histories, we discover that the mass fraction of young stellar populations with age

It is well known that there are few open clusters (OCs) in the high-latitude region of the Milky Way galaxy, because most star formation takes place in the thin disk. It is therefore crucial to look for high Galactic latitude OCs, in order to understand OCs and the Galactic parts outside the plane well. This work looks for high Galactic latitude OCs in Gaia Early Data Release 3, and determines their basic parameters from color–magnitude diagrams (CMDs) if the main sequence is included in CMDs. The friend-of-friend method is applied to the determination of the membership of stars. Star groups with more than 20 bright ( G < 18 mag) stars are taken as OC candidates, and these candidates are finally verified by the observed CMDs including stars fainter than 18 mag in the G band. After crossmatching with previous catalogs, 56 new OC candidates are found in the high Galactic latitude region with ∣ b ∣ ≥ 25°, in which 35 have somewhat clear CMDs and are suggested as newly discovered OCs. Finally, eight of the new OCs are confirmed again by the pyUPMASK technique. The new sample increases the total number of known high Galactic latitude OC candidates significantly. The distance modulus, color excess, metallicity, age, and binary fraction of 35 newly discovered OCs are determined by fitting their observed CMDs to the ASPS stellar population models. All the results are included in the new star cluster catalog, LISC, as its second part (LISC II).

The Study of H α from Dwarf Emissions (SHαDE) is a high spectral resolution (R = 13 500) H α integral field survey of 69 dwarf galaxies with stellar masses 106 < M ⋆ < 109 M⊙. The survey used FLAMES on the ESO Very Large Telescope. SHαDE is designed to study the kinematics and stellar populations of dwarf galaxies using consistent methods applied to massive galaxies and at matching level of detail, connecting these mass ranges in an unbiased way. In this paper, we set out the science goals of SHαDE, describe the sample properties, outline the data reduction, and analysis processes. We investigate the log  M ⋆–log  S 0.5 mass–kinematics scaling relation, which has previously shown potential for combining galaxies of all morphologies in a single scaling relation. We extend the scaling relation from massive galaxies to dwarf galaxies, demonstrating this relation is linear down to a stellar mass of M ⋆ ∼ 108.6 M⊙. Below this limit, the kinematics of galaxies inside one effective radius appears to be dominated by the internal velocity dispersion limit of the H α-emitting gas, giving a bend in the log  M ⋆–log  S 0.5 relation. Replacing stellar mass with total baryonic mass using gas mass estimate reduces the severity but does not remove the linearity limit of the scaling relation. An extrapolation to estimate the galaxies' dark matter halo masses, yields a log  M h–log  S 0.5 scaling relation that is free of any bend, has reduced curvature over the whole mass range, and brings galaxies of all masses and morphologies on to the virial relation. [ABSTRACT FROM AUTHOR]