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We adopt a set of second-order differential equations (k − ω model) to handle core convective overshooting in massive stars, simulate the evolution of nitrogen sequence Wolf–Rayet (WNL) stars with different metallicities and initial masses, both rotating and nonrotating models, and compare the results with the classical overshooting model. The results indicate that, under the same initial conditions, the k − ω model generally produces larger convective cores and wider overshooting regions, thereby increasing the mass ranges and extending the lifetimes of WNL stars, as well as the likelihood of forming WNL stars. The masses and lifetimes of WNL stars both increase with higher metallicities and initial masses. Under higher-metallicity conditions, the two overshooting schemes significantly differ in their impacts on the lifetimes of WNL stars, but are insignificant in the mass ranges of the WNL stars. Rotation may drive the formation of WNL stars in low-mass, metal-poor counterparts, with this effect being more pronounced in the overshooting model. The surface nitrogen of metal-rich WNL stars formed during the main-sequence phase is likely primarily from the CN cycle, while it may come from both the CN and NO cycles for relatively metal-poor counterparts. Our model can effectively explain the distribution of WNL stars in the Milky Way, but appears to have inadequacies in explaining the WNL stars in the LMC. [ABSTRACT FROM AUTHOR]

We combine a new Galactic plane survey of hydrogen radio recombination lines (RRLs) with far-infrared surveys of ionized nitrogen, N+, to determine nitrogen abundance across Galactic radius. RRLs were observed with the NASA Deep Space Network Station 43 70 m antenna and the Green Bank Telescope in 108 lines of sight spanning −135°< l < 60°, at b = 0°. These positions were also observed in [N ii ] 122 μ m and 205 μ m lines with the Herschel Space Observatory. Combining RRL and [N ii ] 122 μ m and 205 μ m observations in 41 of 108 samples with high signal-to-noise ratio, we studied the ionized nitrogen abundance distribution across Galactocentric distances of 0–8 kpc. Combined with existing solar neighborhood and outer Galaxy N/H abundance determinations, we studied this quantity's distribution within the Milky Way's inner 17 kpc for the first time. We found a nitrogen abundance gradient extending from Galactocentric radii of 4–17 kpc in the Galactic plane, while within 0–4 kpc the N/H distribution remained flat. The gradient observed at large Galactocentric distances supports inside-out galaxy growth, with the additional steepening resulting from variable star formation efficiency and/or radial flows in the Galactic disk, while the inner 4 kpc flattening, coinciding with the Galactic bar's onset, may be linked to radial flows induced by the bar potential. Using SOFIA/FIFI-LS and Herschel/PACS, we observed the [N iii ] 57 μ m line to trace doubly ionized gas contribution in a subsample of sight lines. We found negligible N++ contributions along these sight lines, suggesting mostly singly ionized nitrogen originating from low-ionization H ii region outskirts. [ABSTRACT FROM AUTHOR]

Impact of p-capture reactions on the abundances of neon and magnesium considering the nuclear reaction chain, Neon–Sodium–Magnesium–Aluminum (hereafter extended Ne–Al) for stellar conditions of temperature range of 0.02 × 10 9 – 0.10 × 10 9 K and typical density of 100 g cc - 1 has been studied. Then, we have estimated abundances of Ne and Mg, which are of a little special importance. The estimated abundances of these aforesaid elements are then compared with their counterparts, which have been observed in some B-type stars. For those B-type stars, we have discovered a significant agreement in the abundances between the estimated and observed values with a correlation coefficient >0.8. [ABSTRACT FROM AUTHOR]

We report the discovery of a high-velocity, very low-mass star or brown dwarf whose kinematics suggest it is unbound to the Milky Way. CWISE J124909.08+362116.0 was identified by citizen scientists in the Backyard Worlds: Planet 9 program as a high-proper-motion ( μ = 0.″9 yr ^−1 ) faint red source. Moderate-resolution spectroscopy with Keck/NIRES reveals it to be a metal-poor early L subdwarf with a large radial velocity (−103 ± 10 km s ^−1 ), and its estimated distance of 125 ± 8 pc yields a speed of 456 ± 27 km s ^−1 in the Galactic rest frame, near the local escape velocity for the Milky Way. We explore several potential scenarios for the origin of this source, including ejection from the Galactic center ≳3 Gyr in the past, survival as the mass donor companion to an exploded white dwarf, acceleration through a three-body interaction with a black hole binary in a globular cluster, and accretion from a Milky Way satellite system. CWISE J1249+3621 is the first hypervelocity very low-mass star or brown dwarf to be found and the nearest of all such systems. It may represent a broader population of very high-velocity, low-mass objects that have undergone extreme accelerations.

The gas-phase metallicity of galaxies is regulated by multiple astrophysical processes, which makes it a crucial diagnostic of galaxy formation and evolution. Beyond the fundamental mass–metallicity relation, a debate about the secondary galaxy property to predict the metallicity of galaxies arises. Motivated by this, we systematically examine the relationship between gas-phase metallicity and other galaxy properties, i.e., the star formation rate (SFR) and galaxy size, in addition to stellar mass in both observation and simulation. We utilize the data from the Mapping Nearby Galaxies at Apache Point Observatory survey and the TNG50 simulations. We find that the combination of ${M}_{* }/{R}_{{\rm{e}}}^{\beta }$ with β ∼ 0.6–1 is in much stronger correlation to the metallicity than stellar mass alone, regardless of whether the SFR is included or not, in both observation and simulation. This indicates that galaxy size plays a more important role in determining gas-phase metallicity of galaxies than SFR. In addition, The Next Generation simulation predicts that the SFR, although being a subdominant role, becomes increasingly important in the high- z universe. Finally, we speculate that the SFR modulates metallicity on the temporal dimension, synchronized with time-varying gas inflows, and galaxy size regulates metallicity on the spatial dimension by affecting the gravitational potential and the mass-loading factor.

We search for an optimal filter design for the estimation of stellar metallicity, based on synthetic photometry from Gaia XP spectra convolved with a series of filter-transmission curves defined by different central wavelengths and bandwidths. Unlike previous designs based solely on maximizing metallicity sensitivity, we find that the optimal solution provides a balance between the sensitivity and uncertainty of the spectra. With this optimal filter design, the best precision of metallicity estimates for relatively bright ( G ∼ 11.5) stars is excellent, σ _[Fe/H] = 0.034 dex for FGK dwarf stars, superior to that obtained utilizing custom sensitivity-optimized filters (e.g., SkyMapper v ). By selecting hundreds of high-probability member stars of the open cluster M67, our analysis reveals that the intrinsic photometric-metallicity scatter of these cluster members is only 0.036 dex, consistent with this level of precision. Our results clearly demonstrate that the internal precision of photometric-metallicity estimates can be extremely high, even providing the opportunity to perform chemical tagging for very large numbers of field stars in the Milky Way. This experiment shows that it is crucial to take into account uncertainty alongside the sensitivity when designing filters for measuring the stellar metallicity and other parameters.

The unprecedented infrared spectroscopic capabilities of JWST have provided high-quality interstellar medium metallicity measurements and enabled characterization of the gas-phase mass–metallicity relation (MZR) for galaxies at z ≳ 5 for the first time. We analyze the gas-phase MZR and its evolution in a high-redshift suite of FIRE-2 cosmological zoom-in simulations at z = 5–12 and for stellar masses M _* ∼ 10 ^6 –10 ^10 M _⊙ . These simulations implement a multichannel stellar feedback model and produce broadly realistic galaxy properties, including when evolved to z = 0. The simulations predict very weak redshift evolution of the MZR over the redshift range studied, with the normalization of the MZR increasing by less than 0.01 dex as redshift decreases from z = 12 to z = 5. The median MZR in the simulations is well approximated as a constant power-law relation across this redshift range given by $\mathrm{log}(Z/{Z}_{\odot })=0.37\mathrm{log}({M}_{* }/{{\rm{M}}}_{\odot })-4.3$ . We find good agreement between our best-fit model and recent observations made by JWST at high redshift. The weak evolution of the MZR at z > 5 contrasts with the evolution at z ≲ 3, where increasing normalization of the MZR with decreasing redshift is observed and predicted by most models. The FIRE-2 simulations predict increasing scatter in the gas-phase MZR with decreasing stellar mass, in qualitative agreement with some observations.

Cosmic hydrogen reionization and cosmic production of the first metals are major phase transitions of the Universe occurring during the first billion years after the Big Bang; however, these are still underexplored observationally. Using the JWST/NIRSpec prism spectroscopy, we report the discovery of a sub- L _* galaxy at z _spec = 8.1623 ± 0.0007, dubbed RX J2129–z8He II , via the detection of a series of strong rest-frame UV/optical nebular emission lines and the clear Lyman break. RX J2129–z8He II shows a pronounced UV continuum with an extremely steep (i.e., blue) spectral slope of $\beta =-{2.53}_{-0.07}^{+0.06}$ , the steepest among all spectroscopically confirmed galaxies at z _spec ≳ 7, in support of its very hard ionizing spectrum that could lead to a significant leakage of its ionizing flux. Therefore, RX J2129–z8He II is representative of the key galaxy population driving the cosmic reionization. More importantly, we detect a strong He II λ 1640 emission line in its spectrum, one of the highest redshifts at which such a line is robustly detected. Its high rest-frame equivalent width (EW = 21 ± 4 Å) and extreme flux ratios with respect to UV metal and Balmer lines raise the possibility that part of RX J2129–z8He II ’s stellar population could be Pop III (Pop III)-like. Through careful photoionization modeling, we show that the physically calibrated phenomenological models of the ionizing spectra of Pop III stars with strong mass loss can successfully reproduce the emission line flux ratios observed in RX J2129–z8He II . Assuming the Eddington limit, the total mass of the Pop III stars within this system is estimated to be 7.8 ± 1.4 × 10 ^5 M _⊙ . To date, this galaxy presents the most compelling case in the early Universe where trace Pop III stars might coexist with metal-enriched populations.

Cosmic metals are believed to originate from stellar and supernovae (SNe) nucleosynthesis, dispersed into the interstellar medium (ISM) through stellar winds and supernova explosions. In this paper, we present the clear evidence of metal enrichment by a Type Ic SN 2011jm in the galaxy NGC 4809, utilizing high spatial resolution integral field unit observations obtained from the Very Large Telescope/Multi Unit Spectroscopic Explorer. Despite SN 2011jm being surrounded by metal-deficient ISM (∼0.25 Z _⊙ ) at a scale about 100 pc, we clearly detect enriched oxygen abundance (∼0.35 Z _⊙ ) and a noteworthy nitrogen-to-oxygen ratio at the SN site. Remarkably, the metal pollution is confined to a smaller scale (≲13 pc). We posit that the enhanced ionized metal stems from stellar winds emitted by massive stars or previous SN explosions. This observation may represent the first direct detection of chemical pollution by stellar feedback in star-forming galaxies beyond the Local Volume.

In this investigation, we seek to understand the role of non‐nuclear attractors (NNAs) of the neutral Li2 dimer subjected to an electric (±E) field that is directed parallel (±Ex) and perpendicular (±Ey) to the bond‐path. The ±Ex‐fields and ±Ey‐fields are separately applied to the Li2 molecular graph until the bond ruptures. The next generation quantum theory of atoms in molecules (NG‐QTAIM) interpretation of bonding was constructed with the stress tensor σ(r) eigenvectors on the Hessian of ρ(r) molecular graph. The asymmetry induced by both the ±Ey‐field and ±Ex‐field was detected in terms of the rotation of the orthogonal triad of stress tensor σ(r) eigenvectors {e1σ, e2σ, e3σ} relative to the Cartesian coordinate frame. The orthogonal triad of Hessian of ρ(r) eigenvectors {e1, e2, e3} however, were only able to detect rotation induced by the high degree of asymmetry present for bent bond‐paths induced by the ±Ey‐fields. Larger movement of the NNAs along the bond‐path correlated with greater bond critical point (BCP) bond metallicity ξ(rb). The effect of applying the ±Ex‐field was compared with unpublished results on neutral Li2 subject to a stretching distortion. The lack of NNA motion along the bond‐path for the stretching distortion correlated with a lower degree of bond metallicity ξ(rb). The stress tensor σ(r) eigenvectors have a unique ability to detect rotation relative to the Cartesian coordinate frame for high bond‐path symmetry occurring for the bond‐stretching distortion and application of the ±Ex‐field. Suggestions for future work are provided. [ABSTRACT FROM AUTHOR]

We study the relation between the metallicities of ionized and atomic gas in star-forming galaxies at z = 0–3 using the Evolution and Assembly of GaLaxies and their Environments (EAGLE) cosmological, hydrodynamical simulations. This is done by constructing a dense grid of sight lines through the simulated galaxies and obtaining the star formation rate- and H i column density-weighted metallicities, Z SFR and Z H I, for each sightline as proxies for the metallicities of ionized and atomic gas, respectively. We find Z SFR ≳ Z H I for almost all sight lines, with their difference generally increasing with decreasing metallicity. The stellar masses of galaxies do not have a significant effect on this trend, but the positions of the sight lines with respect to the galaxy centers play an important role: the difference between the two metallicities decreases when moving toward the galaxy centers, and saturates to a minimum value in the central regions of galaxies, irrespective of redshift and stellar mass. This implies that the mixing of the two gas phases is most efficient in the central regions of galaxies where sight lines generally have high column densities of H i. However, a high H i column density alone does not guarantee a small difference between the two metallicities. In galaxy outskirts, the inefficiency of the mixing of star-forming gas with H i seems to dominate over the dilution of heavy elements in H i through mixing with the pristine gas. We find good agreement between the available observational data and the Z SFR– Z H I relation predicted by the EAGLE simulations. Though, observed regions with a nuclear starburst mode of star formation appear not to follow the same relation. [ABSTRACT FROM AUTHOR]

In this investigation, we present an analysis of the metallicity distribution that pertains to neutral gas in the local Galactic interstellar medium (ISM). We derive relative ISM metallicities for a sample of 84 sight lines probing diffuse atomic and molecular gas within 4 kpc of the Sun. Our analysis is based in large part on column density measurements reported in the literature for 22 different elements that are commonly studied in interstellar clouds. We supplement the literature data with new column density determinations for certain key elements and several individual sight lines important to our analysis. Our methodology involves comparing the relative gas-phase abundances of many different elements for a given sight line to simultaneously determine the strength of dust depletion in that direction and the overall metallicity offset. We find that many sight lines probe multiple distinct gas regions with different depletion properties, which complicates the metallicity analysis. Nevertheless, our results provide clear evidence that the dispersion in the metallicities of neutral interstellar clouds in the solar neighborhood is small (∼0.10 dex) and only slightly larger than the typical measurement uncertainties. We find no evidence for the existence of very low metallicity gas (as has recently been reported by De Cia et al.) along any of the 84 sight lines in our sample. Our results are consistent with a local Galactic ISM that is well mixed and chemically homogeneous. [ABSTRACT FROM AUTHOR]

We present a sample of 330 blue edge-on low surface brightness galaxies (ELSBGs). To understand the chemical evolution of ELSBGs, we derived the gas-phase abundance and the [ α /Fe] ratio. Compared with star-forming galaxies, ELSBGs show a flatter trend in the mass–metallicity (M *– Z) relation, which suggests that the oxygen abundance enhancement is inefficient. We focused on 77 ELSBGs with H i data and found that the closed-box model cannot explain their gas fraction and metallicity relation, which implies that infall and/or outflow is needed. We derived the [ α /Fe] ratio of normal ELSBG (<109.5 M ⊙) and massive ELSBG (> = 109.5 M ⊙) using single stellar population grids from the MILES stellar library. The mean [ α /Fe] ratios are 0.18 and 0.4 for normal ELSBG and massive ELSBG, respectively. We suggest that the long timescales of star formation and/or metal-rich gas outflow events caused by SNe Ia winds are likely to be responsible for the α -enhancement of massive ELSBGs. [ABSTRACT FROM AUTHOR]

The first stars were born from chemically pristine gas. They were likely massive, and thus they rapidly exploded as supernovae, enriching the surrounding gas with the first heavy elements. In the Local Group, the chemical signatures of the first stellar population were identified among low-mass, long-lived, very metal-poor ([Fe/H] < −2) stars, characterized by high abundances of carbon over iron ([C/Fe] > +0.7): the so-called carbon-enhanced metal-poor stars. Conversely, a similar carbon excess caused by first-star pollution was not found in dense neutral gas traced by absorption systems at different cosmic time. Here we present the detection of 14 very metal-poor, optically thick absorbers at redshift z ∼ 3–4. Among these, 3 are carbon-enhanced and reveal an overabundance with respect to Fe of all the analyzed chemical elements (O, Mg, Al, and Si). Their relative abundances show a distribution with respect to [Fe/H] that is in very good agreement with those observed in nearby very metal-poor stars. All the tests we performed support the idea that these C-rich absorbers preserve the chemical yields of the first stars. Our new findings suggest that the first-star signatures can survive in optically thick but relatively diffuse absorbers, which are not sufficiently dense to sustain star formation and hence are not dominated by the chemical products of normal stars. [ABSTRACT FROM AUTHOR]

Population synthesis models predict that high-mass X-ray binary (HMXB) populations produced in low-metallicity environments should be more X-ray luminous, a trend supported by studies of nearby galaxies. This trend may be responsible for the observed increase of the X-ray luminosity (L X) per star formation rate (SFR) with redshift due to the decrease of metallicity (Z) at fixed stellar mass as a function of redshift. To test this hypothesis, we use a sample of 79 z ∼ 2 star-forming galaxies with oxygen abundance measurements from the MOSDEF survey, which obtained rest-frame optical spectra for ∼1500 galaxies in the CANDELS fields at 1.37 < z < 3.80. Using Chandra data from the Chandra AEGIS-X Deep, Chandra Deep Field North, and Chandra Deep Field South surveys, we stack the X-ray data at the galaxy locations in bins of redshift and Z because the galaxies are too faint to be individually detected. In agreement with previous studies, the average L X/SFR of our z ∼ 2 galaxy sample is enhanced by ≈0.4-0.8 dex relative to local HMXB L X-SFR scaling relations. Splitting our sample by Z, we find that L X/SFR and Z are anticorrelated with 97% confidence. This observed Z dependence for HMXB-dominated galaxies is consistent with both the local L X-SFR-Z relation and a subset of population synthesis models. Although the statistical significance of the observed trends is weak owing to the low X-ray statistics, these results constitute the first direct evidence connecting the redshift evolution of L X/SFR and the Z dependence of HMXBs.

Elemental abundance pattern is one of the key components which gives clues for understanding not only the cluster formation, but also the chemical evolution. But the origin of the abundance pattern is yet to be completely perceived. In this study, we carried out the impact of proton-capture reaction cycles on the abundances of phosphorus (P) and sulfur (S) considering nuclear burning cycles of PCl in stars of temperature range of 0.1 × 10 9 – < 0.7 × 10 9 K and density of 10 2 g cc - 1 . Such kind of temperature density situations are going to be dominant within the H-burning shell of evolved stars. We have estimated abundances of P and S in 22 FGK dwarfs and giants that span - 0.55 < [ Fe / H ] < 0.2 . We observe an excellent agreement of [P/Fe] and [S/Fe] between the estimated and observed abundance values with a correlation coefficient >0.7 and >0.8, respectively, for all 22 FGK stars. Possible sources of these discrepancies are also discussed. [ABSTRACT FROM AUTHOR]

We present a study of nearby dwarf galaxies selected from the Arecibo Legacy Fast ALFA (ALFALFA) blind H i survey. A primary goal of the project was to utilize a nonstandard selection method with the hope of detecting previously unrecognized extremely metal-poor (XMP) galaxies. The study was motivated by the recent discovery of two XMP galaxies, Leo P and Leoncino, which were both originally found via the ALFALFA survey. We have obtained narrowband H α images for 42 dwarf systems, many of which are located in the Local Void in front of the Pisces–Perseus Supercluster. Spectra for 11 of the best candidates resulted in the determination of metal abundances for 10 of the systems. None were found to be extremely metal-poor, although one system (AGC 123350) was found to have an oxygen abundance of log(O/H)+12 = 7.46, or ∼6% solar. One of the galaxies in our sample exhibits a high oxygen abundance for its luminosity, suggesting the possibility that it may have a tidal origin. [ABSTRACT FROM AUTHOR]

We present ultradeep Keck/MOSFIRE rest-optical spectra of two star-forming galaxies at z = 2.18 in the COSMOS field with bright emission lines, representing more than 20 hr of total integration. The fidelity of these spectra enabled the detection of more than 20 unique emission lines for each galaxy, including the first detection of the auroral [O ii ] λλ 7322, 7332 lines at high redshift. We use these measurements to calculate the electron temperature in the low-ionization O+ zone of the ionized interstellar medium and derive abundance ratios of O/H, N/H, and N/O using the direct method. The N/O and α /Fe abundance patterns of these galaxies are consistent with rapid formation timescales and ongoing strong starbursts, in accord with their high specific star formation rates. These results demonstrate the feasibility of using auroral [O ii ] measurements for accurate metallicity studies at high redshift in a higher-metallicity and lower-excitation regime previously unexplored with the direct method in distant galaxies. These results also highlight the difficulty in obtaining the measurements required for direct-method metallicities from the ground. We emphasize the advantages that the JWST/NIRSpec instrument will bring to high-redshift metallicity studies, where the combination of increased sensitivity and uninterrupted wavelength coverage will yield more than an order of magnitude increase in efficiency for multiplexed auroral-line surveys relative to current ground-based facilities. Consequently, the advent of JWST promises to be the beginning of a new era of precision chemical abundance studies of the early universe at a level of detail rivaling that of local galaxy studies. [ABSTRACT FROM AUTHOR]

We present initial results associating galaxies in the Multi-Unit Spectroscopic Explorer (MUSE) Ultra Deep Field (MUDF) with gas seen in absorption along the line of sight to two bright quasars in this field to explore the dependence of metals in the circumgalactic medium (CGM) on galaxy properties. The MUDF includes ∼140 hr of Very Large Telescope (VLT)/MUSE data and 90 orbits of Hubble Space Telescope (HST)/G141M grism observations alongside VLT/Ultraviolet and Visual Echelle Spectrograph spectroscopy of the two quasars and several bands of HST imaging. We compare the metal absorption around galaxies in this field as a function of impact parameter, azimuthal angle, and galaxy metallicity across redshifts 0.5 < z < 3.2. Due to the depth of our data and a large field of view, our analysis extends to low stellar masses (600 kpc). We find a correlation between the absorber equivalent width and the number of nearby galaxies, but do not detect a significant anticorrelation with the impact parameter. Our full sample does not show any significant change in absorber incidence as a function of azimuthal angle. However, we do find a bimodality in the azimuthal angle distribution of absorption at small impact parameters (

We adopt a set of second-order differential equations ( k − ω model) to handle core convective overshooting in massive stars, simulate the evolution of nitrogen sequence Wolf–Rayet (WNL) stars with different metallicities and initial masses, both rotating and nonrotating models, and compare the results with the classical overshooting model. The results indicate that, under the same initial conditions, the k − ω model generally produces larger convective cores and wider overshooting regions, thereby increasing the mass ranges and extending the lifetimes of WNL stars, as well as the likelihood of forming WNL stars. The masses and lifetimes of WNL stars both increase with higher metallicities and initial masses. Under higher-metallicity conditions, the two overshooting schemes significantly differ in their impacts on the lifetimes of WNL stars, but are insignificant in the mass ranges of the WNL stars. Rotation may drive the formation of WNL stars in low-mass, metal-poor counterparts, with this effect being more pronounced in the overshooting model. The surface nitrogen of metal-rich WNL stars formed during the main-sequence phase is likely primarily from the CN cycle, while it may come from both the CN and NO cycles for relatively metal-poor counterparts. Our model can effectively explain the distribution of WNL stars in the Milky Way, but appears to have inadequacies in explaining the WNL stars in the LMC.

We present the integral field spectroscopic observations of ionized gas (H α and [N II ]) using the PCWI, along with deep CO(2–1) observations by the ${}^{\unicode{x02035}}{\bar{{\rm{U}}}}^{\unicode{x02035}}\bar{{\rm{u}}}$ receiver on JCMT for AGC 102004. The velocity field of H α shows an anomalous distribution in the northwestern (NW) disk. The H α spectrum is well-fitted by two Gaussian components, and the weak Gaussian component is dominated by the anomalous H α in the NW disk. The Gaussian fit center of H α emission is offset by +24.2 km s ^−1 from the systemic velocity obtained from the H i emission. We derive the gas-phase metallicity, 12+log(O/H), using [N II ] λ 6583/H α ratio as a proxy. The mean value of 12+log(O/H) is 8.30 ± 0.19 over the whole galaxy. The metallicity in the outer disk is lower than the detection limit of 7.72, indicating the metallicity gradient exists in AGC 102004. We speculate a minor/mini-merger event could have happened to the NW disk. CO(2–1) emission has nondetection in AGC 102004, reaching a noise level of 0.33 mK smoothed to 30 km s ^−1 . The upper limit of molecular gas mass in AGC 102004 is 2.1 × 10 ^7 M _⊙ with X _CO = 3.02 × 10 ^20 cm ^−2 (K km s ^−1 ) ^−1 . The ${M}_{{{\rm{H}}}_{2}}$ / M ${}_{{\rm{H}}\,{\rm{I}}}^{{\rm{corr}}}$ of AGC 102004 is lower than 0.0037 and lower than that of normal galaxies.

We combine a new Galactic plane survey of hydrogen radio recombination lines (RRLs) with far-infrared surveys of ionized nitrogen, N ^+ , to determine nitrogen abundance across Galactic radius. RRLs were observed with the NASA Deep Space Network Station 43 70 m antenna and the Green Bank Telescope in 108 lines of sight spanning −135°< l < 60°, at b = 0°. These positions were also observed in [N ii ] 122 μ m and 205 μ m lines with the Herschel Space Observatory. Combining RRL and [N ii ] 122 μ m and 205 μ m observations in 41 of 108 samples with high signal-to-noise ratio, we studied the ionized nitrogen abundance distribution across Galactocentric distances of 0–8 kpc. Combined with existing solar neighborhood and outer Galaxy N/H abundance determinations, we studied this quantity’s distribution within the Milky Way’s inner 17 kpc for the first time. We found a nitrogen abundance gradient extending from Galactocentric radii of 4–17 kpc in the Galactic plane, while within 0–4 kpc the N/H distribution remained flat. The gradient observed at large Galactocentric distances supports inside-out galaxy growth, with the additional steepening resulting from variable star formation efficiency and/or radial flows in the Galactic disk, while the inner 4 kpc flattening, coinciding with the Galactic bar’s onset, may be linked to radial flows induced by the bar potential. Using SOFIA/FIFI-LS and Herschel/PACS, we observed the [N iii ] 57 μ m line to trace doubly ionized gas contribution in a subsample of sight lines. We found negligible N ^++ contributions along these sight lines, suggesting mostly singly ionized nitrogen originating from low-ionization H ii region outskirts.

We use deep Spitzer mid-infrared spectroscopic maps of radial strips across three nearby galaxies with well-studied metallicity gradients (M101, NGC 628, and NGC 2403) to explore the physical origins of the observed deficit of polycyclic aromatic hydrocarbons (PAHs) at subsolar metallicity (i.e., the PAH–metallicity relation or PZR). These maps allow us to trace the evolution of all PAH features from 5–18 μ m as metallicity decreases continuously from solar ( Z _⊙ ) to 0.2 Z _⊙ . The total PAH-to-dust luminosity ratio remains relatively constant until reaching a threshold of ∼ 2/3 Z _⊙ , below which it declines smoothly but rapidly. The PZR has been attributed to preferential destruction of the smallest grains in the hard radiation environments found at low metallicity. In this scenario, a decrease in emission from the shortest-wavelength PAH features is expected. In contrast, we find a steep decline in long-wavelength power below Z _⊙ , especially in the 17 μ m feature, with the shorter-wavelength PAH bands carrying an increasingly large fraction of power at low metallicity. We use newly developed grain models to reproduce the observed PZR trends, including these variations in fractional PAH feature strengths. The model that best reproduces the data employs an evolving grain size distribution that shifts to smaller sizes as metallicity declines. We interpret this as a result of inhibited grain growth at low metallicity, suggesting continuous replenishment in the interstellar medium is the dominant process shaping the PAH grain population in galaxies.

JWST spectroscopy has revolutionized our understanding of galaxies in the early Universe. Covering wavelengths up to 5.3 μ m, NIRSpec can detect rest-frame optical H α emission lines out to z = 7 and [O iii ] to z = 9.5. Observing these lines in more distant galaxies requires longer wavelength spectroscopy with MIRI. Here we present MIRI Medium Resolution Spectrograph integral field unit observations of the lensed galaxy merger MACS0647–JD at z = 10.165. With exposure times of 4.2 hr in each of two bands (SHORT and LONG), we detect H α at 9 σ , [O iii ] λ 5008 at 11 σ , and [O iii ] λ 4960 at 3 σ . Combined with previously reported NIRSpec spectroscopy that yielded seven emission lines including the auroral line [O iii ] λ 4363, we present the first direct metallicity measurement of a z > 10 galaxy: $12+\mathrm{log}({\rm{O}}/{\rm{H}})=7.79\pm 0.09$ , or ${0.13}_{-0.03}^{+0.02}\,{Z}_{\odot }$ . This is similar to galaxies at z ∼ 4–9 with direct metallicity measurements, though higher than expected given the high specific star formation rate log(sSFR/yr ^−1 ) = −7.4 ± 0.3. We further constrain the ionization parameter $\mathrm{log}(U)$ = −1.9 ± 0.1, ionizing photon production efficiency log( ξ _ion ) = 25.3 ± 0.1, and SFR = 5.0 ± 0.6 M _⊙ yr ^−1 within the past 10 Myr. These observations demonstrate the combined power of JWST NIRSpec and MIRI for studying galaxies in the first 500 million years.

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.

RR Lyrae stars (RRLs) are excellent tracers of stellar populations for old, metal-poor components in the the Milky Way and the Local Group. Their luminosities have a metallicity dependence, but determining spectroscopic [Fe/H] metallicities for RRLs, especially at distances outside the solar neighborhood, is challenging. Using 40 RRLs with metallicities derived from both Fe( ii ) and Fe( i ) abundances, we verify the calibration between the [Fe/H] of RRLs from the calcium triplet. Our calibration is applied to all RRLs with Gaia Radial Velocity Spectrometer (RVS) spectra in Gaia DR3 and to 80 stars in the inner Galaxy from the BRAVA-RR survey. The coadded Gaia RVS RRL spectra provide RRL metallicities with an uncertainty of 0.25 dex, which is a factor of two improvement over the Gaia photometric RRL metallicities. Within our Galactic bulge RRL sample, we find a dominant fraction with low energies without a prominent rotating component. Due to the large fraction of such stars, we interpret these stars as belonging to the in situ metal-poor Galactic bulge component, although we cannot rule out that a fraction of these belong to an ancient accretion event such as Kraken/Heracles.

The ratios of strong rest-frame optical emission lines are the dominant indicators of metallicities in high-redshift galaxies. Since typical strong-line-based metallicity indicators are calibrated on auroral lines at z = 0, their applicability for galaxies in the distant Universe is unclear. In this paper, we make use of mock emission-line data from cosmological simulations to investigate the calibration of rest-frame optical emission lines as metallicity indicators at high redshift. Our model, which couples the simba cosmological galaxy formation simulation with cloudy photoionization calculations, includes contributions from H ii regions, post-asymptotic-giant-branch stars, and diffuse ionized gas (DIG). We find mild redshift evolution in the 12 indicators that we study, which implies that the dominant physical properties that evolve in our simulations do have a discernible impact on the metallicity calibrations at high redshifts. When comparing our calibrations with high-redshift auroral line observations from the James Webb Space Telescope, we find a slight offset between our model results and the observations and find that a higher ionization parameter at high redshifts can be one of the possible explanations. We explore the physics that drives the shapes of strong-line metallicity relationships and propose calibrations for hitherto unexplored low-metallicity regimes. Finally, we study the contribution of DIG to total line fluxes. We find that the contribution of DIG increases with metallicity at z ∼ 0 for singly ionized oxygen and sulfur lines and can be as high as 70%, making it crucial to include their contribution when modeling nebular emission.

We present a new suite of numerical simulations of the star-forming interstellar medium (ISM) in galactic disks using the TIGRESS-NCR framework. Distinctive aspects of our simulation suite are (1) sophisticated and comprehensive numerical treatments of essential physical processes including magnetohydrodynamics, self-gravity, and galactic differential rotation, as well as photochemistry, cooling, and heating coupled with direct ray-tracing UV radiation transfer and resolved supernova feedback and (2) wide parameter coverage including the variation in metallicity over $Z^{\prime} \equiv Z/{Z}_{\odot }\sim 0.1-3$ , gas surface density Σ _gas ∼ 5–150 M _⊙ pc ^−2 , and stellar surface density Σ _star ∼ 1–50 M _⊙ pc ^−2 . The range of emergent star formation rate surface density is Σ _SFR ∼ 10 ^−4 –0.5 M _⊙ kpc ^−2 yr ^−1 , and ISM total midplane pressure is P _tot / k _B = 10 ^3 –10 ^6 cm ^−3 K, with P _tot equal to the ISM weight ${ \mathcal W }$ . For given Σ _gas and Σ _star , we find ${{\rm{\Sigma }}}_{\mathrm{SFR}}\propto Z{{\prime} }^{0.3}$ . We provide an interpretation based on the pressure-regulated feedback-modulated (PRFM) star formation theory. The total midplane pressure consists of thermal, turbulent, and magnetic stresses. We characterize feedback modulation in terms of the yield ϒ, defined as the ratio of each stress to Σ _SFR . The thermal feedback yield varies sensitively with both weight and metallicity as ${{\rm{\Upsilon }}}_{\mathrm{th}}\propto {{ \mathcal W }}^{-0.46}Z{{\prime} }^{-0.53}$ , while the combined turbulent and magnetic feedback yield shows weaker dependence ${{\rm{\Upsilon }}}_{\mathrm{turb}+\mathrm{mag}}\propto {{ \mathcal W }}^{-0.22}Z{{\prime} }^{-0.18}$ . The reduction in Σ _SFR at low metallicity is due mainly to enhanced thermal feedback yield, resulting from reduced attenuation of UV radiation. With the metallicity-dependent calibrations we provide, PRFM theory can be used for a new subgrid star formation prescription in cosmological simulations where the ISM is unresolved.

We present a JWST imaging survey with NIRCam and MIRI of NGC 346, the brightest star-forming region in the Small Magellanic Cloud. By combining aperture and point-spread function photometry of 11 wavelength bands across these two instruments, we have detected more than 200,000 unique sources. Using a near-infrared color analysis, we observe various evolved and young populations, including 196 young stellar objects (YSOs) and pre-main-sequence stars suitable for forthcoming spectroscopic studies. We expand upon this work, creating mid-infrared color–magnitude diagrams and determining color cuts to identify 833 reddened sources which are YSO candidates. We observe that these candidate sources are spatially associated with regions of dusty, filamentary nebulosity. Furthermore, we fit model YSO spectral energy distributions to a selection of sources with detections across all of our MIRI bands. We classify with a high degree of confidence 23 YSOs in this sample and estimate their radii, bolometric temperatures, luminosities, and masses. We detect YSOs approaching 1 M _⊙ , the lowest-mass extragalactic YSOs confirmed to date.

We present deep JWST NIRSpec observations in the sight line of MACS J1149.5+2223, a massive cluster of galaxies at z = 0.54. We report the spectroscopic redshift of 28 sources at 3 < z < 9.1, including nine sources with the detection of the ${\left[{\rm{O}}\,{\rm\small{III}}\right]}_{\lambda 4363}$ auroral line. Combining these with 16 ${\left[{\rm{O}}\,{\rm\small{III}}\right]}_{\lambda 4363}$ -detected sources from publicly available JWST data, our sample consists of 25 galaxies with robust gas-phase metallicity measurements via the direct method. We observe a positive correlation between stellar mass and metallicity, with an ∼0.5 dex offset down below the local relation. Interestingly, we find a larger-than-expected scatter of ∼0.3 dex around the relation, which cannot be explained by redshift evolution among our sample or other third parameters. The scatter increases at higher redshift, and we tentatively attribute this to the enrichment process having higher stochasticity, due to shallower potential wells, more intense feedback processes, and a higher galaxy merger rate. Despite reaching a considerably low-mass regime ( $\mathrm{log}{M}_{* }/{M}_{\odot }\sim 7.3$ ), our samples have metallicity of $\mathrm{log}({\rm{O}}/{\rm{H}})$ +12 ≳ 7, i.e., comparable to the most metal-poor galaxies in the local Universe. The search for primordial galaxies may be accomplished by extending toward a lower mass and/or by investigating inhomogeneities at smaller spatial scales. Lastly, we investigate potential systematics caused by the limitation of JWST’s Micro-Shutter Assembly observations. Caution is warranted when the target exceeds the slit size, as this situation could allow an overestimation of global metallicity, especially under the presence of a strong negative metallicity gradient.

The role of metallicity in shaping protoplanetary disk evolution remains poorly comprehended. This study analyzes the disk fraction of 10 young (0.9–2.1 Myr) and low-metallicity (0.34–0.83 Z _⊙ ) clusters located in the outer Milky Way with Galactocentric distances between 10 and 13 kpc. Using JHK data obtained from UKIDSS, the calculated disk fraction values for low-mass stars (0.2–2 M _⊙ ) ranged from 42% to 7%. To enhance the statistical reliability of our analysis, eight additional low-metallicity clusters are sourced from previous studies with metallicity range 0.25–0.85 Z _⊙ along with our sample, resulting in a total of 18 regions with low metallicity. We find that low-metallicity clusters exhibit on average a 2.6 ± 0.2 times lower disk fraction compared to solar-metallicity clusters in all the age bins we have. Within the age range we can probe, our study does not find evidence of faster disk decay in subsolar-metallicity regions compared to solar-metallicity regions. Furthermore, we observe a positive correlation between cluster disk fraction and metallicity for two different age groups of 0.3–1.4 and 1.4–2.5 Myr. We emphasize that both cluster age and metallicity significantly affect the fraction of stars with evidence of inner disks.

The photometric colors of globular clusters (GCs) act as effective proxies for metallicity, since all normally used optical/IR color indices exhibit a nonlinear but monotonic relation between their integrated color and their metallicity. One color index, ( g − z ) or (F475W–F850LP), has been spectroscopically calibrated in several studies, providing leverage to define color-to-metallicity conversions for other indices. In this paper, building on the work of Hartman et al., we study the GC color-metallicity relation in more detail by testing the dependence of the relations on different suites of stellar models and different assumed GC ages. Though noticeable differences between models exist, we find that the net effect on the derived GCS metallicity distributions is small.

Both simulations and observations suggest that the disk assembly of galaxies is governed by the interplay between coplanar gas inflow, ex-planar gas outflow, and in situ star formation on the disk, known as the leaky accretion disk. This scenario predicts a strong connection between radial distributions of star formation and chemical abundances. The Milky Way, being the sole Galaxy where we can reliably measure star formation histories and the corresponding temporally resolved chemical abundances with individual stars, provides a unique opportunity to scrutinize this scenario. Based on the recent large spectroscopic and photometric surveys of Milky Way stars, we obtain the radial profiles of magnesium abundance ([Mg/H]) and star formation rate surface density at different lookback times. We find the radial profiles of [Mg/H] can be well-reproduced using the leaky accretion disk model with only two free parameters for stars formed within 4 Gyr, as well as the flattening at large radii of metallicity profiles traced by H ii regions and Cepheids. Furthermore, the constraint effective yield of the Milky Way and nearby galaxies shows broad consistency with the theoretical predictions from the stellar chemical evolution model with a mass-loading factor of 0–2. These results support that the recent assembly of the Milky Way adheres to the leaky accretion disk scenario, bridging the disk formation of our home Galaxy to the big picture of disk formation in the Universe.

Giant planets exhibit diverse orbital properties, hinting at their distinct formation and dynamic histories. In this paper, using Gaia Data Release 3 (DR3), we investigate if and how the orbital properties of Jupiters are linked to their host star properties, particularly their metallicity and age. We obtain metallicities for main-sequence stars of spectral type F, G, and K, hosting hot, warm, and cold Jupiters with varying eccentricities. We compute the velocity dispersions of the host stars of these three groups using kinematic information from Gaia DR3 and obtain average ages using a velocity dispersion–age relation. We find that the host stars of hot Jupiters are relatively metal rich ([Fe/H] = 0.18 ± 0.13) and young (median age of 3.97 ± 0.51 Gyr) compared to the host stars of cold Jupiters in nearly circular orbits, which are relatively metal poor (0.03 ± 0.18) and older (median age of 6.07 ± 0.79 Gyr). The host stars of cold Jupiters in high-eccentricity orbits, on the other hand, show metallicities similar to those of the hosts of hot Jupiters, but are older, on average (median age of 6.25 ± 0.92 Gyr). The similarity in metallicity between the hosts of hot Jupiters and the hosts of cold Jupiters in high-eccentricity orbits supports high-eccentricity migration as the potential origin of hot Jupiters, with the latter serving as the progenitors of hot Jupiters. However, the average age difference between them suggests that the older hot Jupiters may have been engulfed by their host star over timescales ∼ 6 Gyr. This allows us to estimate the value of stellar tidal quality factor, ${Q}_{* }^{{\prime} }\sim {10}^{6\pm 1}$ .

We conducted an investigation of the Coma cluster of galaxies by running a series of constrained hydrodynamic simulations with GIZMO-SIMBA and GADGET-3 based on initial conditions reconstructed from the SDSS survey volume in the ELUCID project. We compared simulation predictions and observations for galaxies, intracluster medium (ICM) and intergalactic medium (IGM) in and around the Coma cluster to constrain galaxy formation physics. Our results demonstrate that this type of constrained investigation allows us to probe in more detail the implemented physical processes, because the comparison between simulations and observations is free of cosmic variance and hence can be conducted in a “one-to-one” manner. We found that an increase in the earlier star formation rate and the supernova feedback of the original GIZMO-SIMBA model is needed to match observational data on stellar, interstellar medium, and ICM metallicity. The simulations without active galactic nucleus (AGN) feedback can well reproduce the observational ICM electron density, temperature, and entropy profiles, ICM substructures, and the IGM temperature–density relation, while the ones with AGN feedback usually fail. However, one requires something like AGN feedback to reproduce a sufficiently large population of quiescent galaxies, particularly in low-density regions. The constrained simulations of the Coma cluster thus provide a test bed to understand processes that drive galaxy formation and evolution.

Using more than 100 galaxies in the MUSE Ultra Deep Field with spectroscopy from the Hubble Space Telescope’s (HST) Wide Field Camera 3 and the Very Large Telescope’s Multi Unit Spectroscopic Explorer, we extend the gas-phase mass–metallicity relation (MZR) at z ≈ 1–2 down to stellar masses of M _⋆ ≈ 10 ^7.5 M _⊙ . The sample reaches 6 times lower in stellar mass and star formation rate (SFR) than previous HST studies at these redshifts, and we find that galaxy metallicities decrease to log(O/H) + 12 ≈ 7.8 ± 0.1 (15% solar) at log( M _⋆ / M _⊙ ) ≈ 7.5, without evidence of a turnover in the shape of the MZR at low masses. We validate our strong-line metallicities using the direct method for sources with [O iii ] λ 4363 and [O iii ] λ 1666 detections, and find excellent agreement between the techniques. The [O iii ] λ 1666-based metallicities double existing measurements with a signal-to-noise ratio ≥ 5 for unlensed sources at z > 1, validating the strong-line calibrations up to z ∼ 2.5. We confirm that the MZR resides ∼0.3 dex lower in metallicity than local galaxies and is consistent with the fundamental metallicity relation if the low-mass slope varies with SFR. At lower redshifts ( z ∼ 0.5) our sample reaches ∼0.5 dex lower in SFR than current calibrations and we find enhanced metallicities that are consistent with extrapolating the MZR to lower SFRs. Finally, we detect only an ∼0.1 dex difference in the metallicities of galaxies in groups versus isolated environments. These results are based on robust calibrations and reach the lowest masses and SFRs that are accessible with HST, providing a critical foundation for studies with the Webb and Roman Space Telescopes.

Determination of fundamental parameters of stars impacts all fields of astrophysics, from galaxy evolution to constraining the internal structure of exoplanets. This paper presents a detailed spectroscopic analysis of Barnard’s star (otherwise known as Gl 699) that compares an exceptionally high-quality (an average signal-to-noise ratio of ∼1000 in the entire domain), high-resolution near-infrared (NIR) spectrum taken with Canada-France-Hawaii Telescope/SPIRou to PHOENIX-ACES stellar atmosphere models. The observed spectrum shows thousands of lines not identified in the models with a similarly large number of lines present in the model but not in the observed data. We also identify several other caveats, such as continuum mismatch, unresolved contamination, and spectral lines significantly shifted from their expected wavelengths; all of these can be a source of bias for the determination of abundance. Out of >10 ^4 observed lines in the NIR that could be used for chemical spectroscopy, we identify a short list of a few hundred lines that are reliable. We present a novel method for determining the effective temperature ( T _eff ) and overall metallicity of slowly rotating M dwarfs that uses several groups of lines as opposed to bulk spectral fitting methods. With this method, we infer T _eff = 3231 ± 21 K for Barnard's star, consistent with the value of 3238 ± 11 K inferred from the interferometric method. We also provide measurements of the abundance of 15 different elements for Barnard's star, including the abundances of four elements (K, O, Y, Th) never reported before for this star. This work emphasizes the need to improve current atmosphere models to fully exploit the NIR domain for chemical spectroscopy analysis.

We present AspGap, a new approach to inferring stellar labels from the low-resolution Gaia XP spectra, including precise [ α /M] estimates—the first time these are obtained by such an approach. AspGap is a neural-network-based regression model trained on APOGEE spectra. In the training step, AspGap learns to use not only XP spectra to predict stellar labels but also the high-resolution APOGEE spectra that lead to the same stellar labels. The inclusion of this last model component—dubbed the hallucinator—creates a more physically motivated mapping and significantly improves the prediction of stellar labels in the validation, particularly that of [ α /M]. For giant stars, we find cross-validated rms accuracies for T _eff , log g , [M/H], and [ α /M] of ∼1%, 0.12 dex, 0.07 dex, and 0.03 dex, respectively. We also validate our labels through comparison with external data sets and through a range of astrophysical tests that demonstrate that we are indeed determining [ α /M] from the XP spectra, rather than just inferring it indirectly from correlations with other labels. We publicly release the AspGap codebase, along with our stellar parameter catalog for all giants observed by Gaia XP. AspGap enables the discovery of new insights into the formation and chemodynamics of our Galaxy by providing precise [ α /M] estimates for 37 million giant stars, including 14 million with radial velocities from Gaia.

Drawing from the Chandra archive and using a carefully selected set of nearby dwarf galaxies, we present a calibrated high-mass X-ray binary (HMXB) luminosity function in the low-mass galaxy regime and search for an already hinted at dependence on metallicity. Our study introduces a new sample of local dwarf galaxies ( D < 12.5 Mpc and M _* < 5 × 10 ^9 M _⊙ ), expanding the specific star formation rates (sSFR) and gas-phase metallicities probed in previous investigations. Our analysis of the observed X-ray luminosity function indicates a shallower power-law slope for the dwarf galaxy HMXB population. In our study, we focus on dwarf galaxies that are more representative in terms of sSFR compared to prior work. In this regime, the HMXB luminosity function exhibits significant stochastic sampling at high luminosities. This likely accounts for the pronounced scatter observed in the galaxy-integrated HMXB population’s L _X /SFR versus metallicity for our galaxy sample. Our calibration is necessary to understand the active galactic nuclei content of low-mass galaxies identified in current and future X-ray survey fields and has implications for binary population synthesis models, as well as X-ray-driven cosmic heating in the early Universe.

The massive end of the gas-phase mass–metallicity relation (MZR) is a sensitive probe of active galactic nuclei (AGN) feedback that is a crucial but highly uncertain component of galaxy evolution models. In this paper, we extend the z ∼ 0.7 MZR by ∼0.5 dex up to log ( M _⋆ / M _⊙ ) ∼ 11.1. We use extremely deep VLT VIMOS spectra from the Large Early Galaxy Astrophysics Census (LEGA-C) survey to measure metallicities for 145 galaxies. The LEGA-C MZR matches the normalization of the z ∼ 0.8 DEEP2 MZR where they overlap, so we combine the two to create an MZR spanning from 9.3 to 11.1 log ( M _⋆ / M _⊙ ). The LEGA-C+DEEP2 MZR at z ∼ 0.7 is offset to slightly lower metallicities (0.05–0.13 dex) than the z ∼ 0 MZR, but it otherwise mirrors the established power-law rise at low/intermediate stellar masses and asymptotic flattening at high stellar masses. We compare the LEGA-C+DEEP2 MZR to the MZR from two cosmological simulations (IllustrisTNG and SIMBA), which predict qualitatively different metallicity trends for high-mass galaxies. This comparison highlights that our extended MZR provides a crucial observational constraint for galaxy evolution models in a mass regime where the MZR is very sensitive to choices about the implementation of AGN feedback.

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.

The color index ( J − K ) _0 of tip-red-giant branch (TRGB) is used to study the metallicity distribution in the Large and Small Magellanic Cloud. With the most complete and pure sample of red member stars so far, the areas are divided into 154 and 70 bins for the LMC and SMC, respectively, with similar number of stars by the Voronoi binning. For each bin, the position of TRGB on the near-infrared color–magnitude diagram, specifically ( J − K ) _0 / K _0 , is determined by the poison-noise weighted method. Converting the color index of TRGB into metallicity, the metallicity gradients in the LMC and the SMC are obtained in four major directions. For the LMC, the gradient to the north is −0.006 ± 0.004 dex kpc ^−1 , to the south −0.010 ± 0.005 dex kpc ^−1 , to the east −0.006 ± 0.003 dex kpc ^−1 , and to the west −0.010 ± 0.003 dex kpc ^−1 . The farthest distance extends to 16 kpc. For the SMC, the gradients to the north, south, east, and west are −0.017 ± 0.031 dex kpc ^−1 , −0.016 ± 0.007 dex kpc ^−1 , −0.003 ± 0.002 dex kpc ^−1 , and −0.004 ± 0.003 dex kpc ^−1 , respectively. The farthest distance for the SMC extends to 27 kpc. The gradient is large from the center to 1 kpc.

Extremely metal-poor galaxies (XMPGs) at relatively low redshift are excellent laboratories for studying galaxy formation and evolution in the early universe. Much effort has been spent on identifying them from large-scale spectroscopic surveys or spectroscopic follow-up observations. Previous work has identified a few hundred XMPGs. In this work, we obtain a large sample of 223 XMPGs at z < 1 from the early data of the Dark Energy Spectroscopic Instrument (DESI). The oxygen abundance is determined using the direct T _e method based on the detection of the [O iii ] λ 4363 line. The sample includes 95 confirmed XMPGs based on the oxygen abundance uncertainty; the remaining 128 galaxies are regarded as XMPG candidates. These XMPGs are only 0.01% of the total DESI observed galaxies. Their coordinates and other properties are provided in the paper. The most XMPGs have an oxygen abundance of ∼1/34 Z _⊙ , a stellar mass of about 1.5 × 10 ^7 M _⊙, and a star formation rate of 0.22 M _⊙ yr ^−1 . The two most XMPGs present distinct morphologies suggesting different formation mechanisms. The local environmental investigation shows that XMPGs preferentially reside in relatively low-density regions. Many of them fall below the stellar mass–metallicity relations (MZRs) of normal star-forming galaxies. From a comparison of the MZR with theoretical simulations, it appears that XMPGs are good analogs to high-redshift star-forming galaxies. The nature of these XMPG populations will be further investigated in detail with larger and more complete samples from the ongoing DESI survey.

Using an updated and significantly augmented sample of Cepheid and tip of the red giant branch (TRGB) distances to 28 nearby spiral and irregular galaxies, covering a wide range of metallicities, we have searched for evidence of a correlation of the zero-point of the Cepheid period–luminosity relation with H ii region (gas-phase) metallicities. Our analysis, for the 21 galaxies closer than 12.5 Mpc, results in the following conclusions: (1) The zero-points of the Cepheid and TRGB distance scales are in remarkably good agreement, with the mean offset in the zero-points of the most nearby distance-selected sample being close to zero, Δ μ _o (Cepheid—TRGB) = −0.026 ± 0.015 mag (for an I -band TRGB zero-point of M _I = −4.05 mag); however, for the more distant sample, there is a larger offset between the two distance scales, amounting to −0.073 ± 0.057 mag 〈Δ μ _o 〉 (Cepheids—TRGB) = −0.026 ± 0.015 mag, for an I -band TRGB zero-point of M _I = −4.05 mag. (2) The individual differences, about that mean, have a measured scatter of ±0.068 mag. (3) We find no statistically significant evidence for a metallicity dependence in the Cepheid distance scale using the reddening-free W ( V , VI ) period–luminosity relation: Δ μ _o ( Cepheid − TRGB ) = − 0.022( ± 0.015) × ([O/H] − 8.50) − 0.003(±0.007).

We examine the relationship between metallicity and J − K color for 64 benchmark late-M and L dwarfs, all of which are wide companions to higher-mass stars, and six of which are new discoveries. We assess the correlation between the Δ( J − K ) color anomaly (the difference in an object’s J − K color from the median color for field objects of the same spectral type) and the metallicity of the host star to investigate how metallicity affects ultracool photospheres. Using Spearman’s rank correlation test and Student’s t-test, the late-M dwarf (L dwarf) sample’s Δ( J − K ) and metallicity show a positive correlation at the 95% (90%) confidence level. A linear fit to color anomaly as a function of metallicity finds a slope of 0.17 ± 0.07 for the late-M dwarfs and a slope of ${0.20}_{-0.08}^{+0.07}$ for the L dwarfs. We also computed the Δ( J − K ) versus metallicity relationship predicted by multi-metallicity model spectra generated using Drift-Phoenix. The modeled late-M dwarfs show a slope of 0.202 ± 0.03, which is close to our observational results, but the modeled L dwarfs show a slope of 0.493 ± 0.02, steeper than our observational results. Both our empirical results and the models indicate that more metal-rich objects should appear redder photometrically. We speculate that higher metallicity drives more condensate formation in these atmospheres, thus making these ultracool dwarfs appear redder.

Multiband light curves of two RR Lyrae variables in Segue II and Ursa Major II ultrafaint dwarf galaxies were collected from near simultaneous observations using the Lulin One-meter Telescope in Vgri bands. Together with Gaia G -band light curves, we determined photometric metallicities using empirical relations involving pulsation period and Fourier parameter as dependent parameters. We demonstrated that the RR Lyrae photometric metallicity can be determined accurately when these empirical relations were employed at multiple wavelengths, which can potentially improve the distance determination based on RR Lyrae stars. The photometric metallicities based on our approach were found to be −2.27 ± 0.13 dex and −1.87 ± 0.16 dex for the RR Lyrae in Segue II and Ursa Major II UFD, respectively, with corresponding distance moduli of 17.69 ± 0.15 mag and 17.58 ± 0.15 mag, in agreement with previous literature determinations. This approach of photometric metallicity of RR Lyrae based on multiband optical light curves will be particularly relevant for distance measurements in the era of the Vera C Rubin’s Legacy Survey of Space and Time.