The effect of supernovae (SNe) on star formation in the interstellar medium (ISM) depends sensitively on where SNe explode with respect to ISM clouds. Observationally, SN ISM environments characterized by spatially resolved gas maps can empirically guide the placement of SNe in subgrid models, but unfortunately such measurements remain scarce, as SNe are rare and often distant. Here we demonstrate a new approach-mapping the ISM around evolved massive stars that are soon to explode. These provide a substantially larger sample of "explosion sites" (than just historical SNe) in nearby galaxies that have high-resolution atomic and molecular ISM maps from the Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. We demonstrate this technique in the well-resolved Local Group spiral M33 by analyzing the 50 pc scale projected ISM densities around red supergiants (RSGs; 8-30 M(circle dot )stars) Wolf-Rayet stars (W-Rs; >30M(circle dot )stars), and supernova remnants. We find a mass-dependent correlation between stars and gas clouds, with at least 45% of W-Rs and up to 77% of RSGs having no detectable H-2 at their pixel locations. In the sample with H-2 detections, we find that more-massive younger progenitors are coincident with denser gas. We show that the density distributions for stars >15 M(circle dot )are statistically distinct from random alignment of stars and gas in M33. Our work provides the first observationally derived estimate of the fraction of the SN-producing stellar population correlated with ISM density peaks. We demonstrate how this can be compared with galaxy simulations, and advocate similar comparisons to the community for constraining subgrid models.

Owing to their proximity to the Milky Way, the Large and Small Magellanic Clouds (L/SMC) uniquely probe the evolution of low-mass galaxies undergoing mutual interactions. In this work, we investigate the connection between the star formation histories (SFHs) of the L/SMC measured from Hubble Space Telescope imaging in the Scylla survey and APOGEE chemical abundances. We model the chemical evolution of the L/SMC in the [Mg/Fe]-[Fe/H] plane within a robust statistical framework to predict chemical abundance signatures resulting directly from starbursts in Scylla SFHs. Both the L/SMC rapidly enrich to high metallicity ([Fe/H] greater than or similar to -1) within 3 Gyr, followed by slower chemical evolution regulated by sequential starbursts, where the SMC may require higher Fe yields from Type Ia supernovae than the LMC. We also model the [Mg/Fe]-[Fe/H] plane to infer starburst properties across distinct spatial regions in the L/SMC. We identify dominant starbursts in the L/SMC with broadly similar timing, though the SMC may host an earlier burst and larger burst strength in the LMC. The global starburst properties are nearly uniform across the LMC disk, whereas the dominant SMC population experiences a stronger and later-onset burst in its eastern wing compared to the main body. We also find evidence for a chemically distinct secondary population in the SMC that preferentially traces the foreground and may originate from the LMC. We discuss the implications of these results for the evolutionary history of the L/SMC and for starbursts in interacting low-mass galaxy pairs.

The emissivity of dust is known to vary greatly with radiative environment, density, grain chemistry, and geometry. Discrepancies between dust mass surface densities derived from far-infrared (FIR) emission and visible extinction persist across and within galaxies in the local Universe. Here, we use new extinction and emission measurements towards the LMC to show that this discrepancy is driven by the dust mass opacity evolving with the intrinsic density of the ISM, and that the ratio between FIR and optical dust mass opacity varies with gas surface density. These new findings imply that the dust mass opacity in the FIR could increase by nearly an order of magnitude (e.g., κ_160 = 0.3 - 6 m^2 kg^-2) across over an order of magnitude of total hydrogen surface density (Σ_H = 4 - 100 M_⊙ pc^-2), corroborating previous theoretical models for dust mass opacity evolution in the FIR, and providing new implications for emission-based dust mass estimates.

We present a three-dimensional model of the local interstellar radiation field (ISRF) in the ultraviolet (UV). Using UV flux measurements from the TD1 catalog and stellar distances from Gaia and Hipparcos, we construct a catalog of stars that we expect to dominate the UV flux in the nearby Galaxy. We use the radiative transfer code DIRTY to model the propagation of photons from these stars through a 3D dust map, including the effects of scattering and absorption. The result is LightCube, a model of the ultraviolet ISRF out to 1.25 kpc from the Sun, with a maximum linear resolution of 1 pc. We model the ISRF in the four TD1 bands (1565 A, 1965 A, 2365 A, and 2740 A), as well as a single value for the full FUV range, and calculate the ISRF at the Sun to be 5.65×10^-14 erg cm^-3 from 912 A to 2000 A. The modeled ISRF is quite variable, with more than an order of magnitude variation seen in dense regions, and about half that in lower density regions. By comparing LightCube to an estimate of the 3D distribution of total-to-selective extinction ratio, R_V, we find a positive correlation between UV flux and R_V in regions of low UV radiation.

We measure the star formation histories (SFHs) from the Scylla survey in ∼98,000 pc ^2 and ∼75,000 pc ^2 of the Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC), respectively, using deep Hubble Space Telescope imaging (80% complete to > 1 mag below the ancient main-sequence turnoff, ∼25.1 and 26.0 mag in F475W and F814W) from 74 pointings. We group the fields into eight subregions in the SMC and seven in the LMC. We use the birth rate parameter to identify bursts of star formation and measure their properties in each subregion. Our methodology provides a standardized framework for burst identification and reveals both broad and fine burst characteristics. We identify global and local bursts, defined as those occurring in ≥half or

Dust extinction curves provide one of the main avenues to understanding the detailed nature of dust grains and accounting for the effects of dust on observations of many astrophysical objects. For the first time, spectroscopic ultraviolet (UV) extinction curves are measured in M33 expanding the sample of Local Group galaxies with such measurements to five. These curves are based on Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra and literature photometry from the UV to the near-infrared. The four measured curves show large variations in their UV shapes including their 2175 & Aring; bump and UV slope strengths. The average extinction of these four sightlines is lower than the averages for other Local Group Galaxies and does not follow the Milky Way (MW) R(V)-dependent relationship. The variations between UV extinction shape parameters and gas-to-dust ratios for the M33 sightlines fall within the variations seen in the combined sample of UV extinction curves in the MW, Large and Small Magellanic Clouds, and M31. The correlation with gas-to-dust ratio is much stronger than the correlation with global metallicity. This strengthens the picture that local conditions like radiation field density and shocks dominate over global galaxy properties like metallicity in determining the wavelength dependence of dust extinction.

The Barbara A. Mikulski Archive for Space Telescopes (MAST) hosts science-ready data products from over 20 NASA missions plus community-contributed data collections and other select surveys. The data support forefront research in the ultraviolet, optical, and near-infrared wavelength bands. We have constructed bibliographies for each mission from publications in nearly 40 professional journals and identified more than 37,000 refereed articles where investigators made a science usage of data hosted in MAST. The publication rate over the last 50 yr shows that most MAST missions have had very high productivity during their in-service lifetimes and have remained so for years or decades afterward. Annual citations of these publications, a measure of impact on research, are robust for most missions, with citations that grow over more than a decade. Most of the citations come from about 10% of the articles within each mission. We examined the bibliographies of the active missions Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) in greater detail. For HST, the rate of archival publications exceeded those authored by the original observing teams within a decade of launch and is now more than 3 times higher. Early indications hint that JWST archival articles could dominate the publication rate even sooner. The production of articles resulting from any given observing program can extend for decades. Programs with small and very large allocations of observing time tend to be particularly productive per unit of observing time. For HST in general, a first publication appears within 1.5 yr for 50% of observing programs and within 3.8 yr for 80% of programs. We discuss various external factors that affect publication metrics, their strengths and limitations for measuring scientific impact, and the challenges of making meaningful comparisons of publication metrics across missions.

We present the first localized detections of the cold neutral medium (CNM) in IC 10, offering a rare view of dense atomic gas in a low-metallicity ( Z / Z _⊙ ∼ 0.27) dwarf galaxy. As a low-metallicity starburst, IC 10’s interstellar medium conditions could reflect small scale physics conditions that mirror those of early galaxies, providing a unique window into the heating and cooling processes that shaped the interstellar medium in early-Universe environments. Leveraging the high angular (<5″ ∼ 15 pc) and spectral (0.4 km s ^−1 ) resolution of the Local Group L -band Survey, we searched for H I absorption against nine continuum radio sources and detected absorption along three sightlines corresponding to internal radio emission sources within IC 10. Using Gaussian decomposition and radiative transfer, we characterize the CNM, deriving spin temperatures of ∼30–55 K, column densities of (0.6–3.0) × 10 ^21 cm ^−2 , cold H I fractions of ∼21%–37%, and line widths of ∼5.6–13.6 km s ^−1 . For each individual detection of H I absorption, we find corresponding molecular emission from ^12 CO ( J = 1–0), HCO ^+ ( J = 1–0), and HCN ( J = 1–0) at similar velocities and with comparable line widths, indicating a well-mixed cold atomic and molecular medium. In IC 10, the CNM shows a clear kinematic connection to the high-density ISM, implying a stronger dynamical coupling with molecular gas than in the Milky Way, in line with expectations for low-metallicity environments. At the ∼15 pc scales probed by slightly extended H II regions in IC 10, unresolved CNM clouds likely contribute to line blending, so the observed broad H I line widths may partly reflect spatial and kinematic averaging.

We use atomic hydrogen (HI) absorption detections from the GASKAP-HI survey to investigate the properties of cold atomic gas in the Large Magellanic Cloud (LMC). Using the radiative transfer method, we decompose 155 sightlines into 330 cold neutral medium (CNM), 2 thermally unstable neutral medium (UNM), and 310 warm neutral medium (WNM) components. We find that the CNM in the LMC exhibits higher optical depths (median 0.46), lower spin temperatures (median ∼37 K), broader linewidths (median ∼4.9 km s^-1), and slightly lower CNM fractions (median ∼23

We present a novel methodology for mapping dust extinction in nearby galaxies at parsec-scale resolution. We apply it to 68 Hubble Space Telescope (HST) fields within the Small and Large Magellanic Clouds (23 fields in the SMC and 45 fields in the LMC) using multiband HST photometry from the Scylla and Metal Evolution Transport and Abundance in the LMC surveys. Our technique leverages kriging, a geostatistical interpolation method built on the principles of Gaussian process regression, combined with Gaussian mixture modeling to statistically isolate background stellar sources and account for line-of-sight depth effects. Three-dimensional dust simulations demonstrate the method's capability to recover column densities to an accuracy of AV approximate to 0.1 mag in fields with at least 1000 sources. The resulting 4 '' resolution (similar to 1 pc) dust maps reveal detailed structure and strong spatial correlation with ancillary interstellar medium (ISM) tracers, especially in star-forming regions like 30 Doradus. Global extinction of total column densities follows log-normal profiles in both galaxies, with the SMC exhibiting slightly higher mean extinction (e mu = 0.47 mag) than the broader LMC (e mu = 0.43 mag), likely due to significant line-of-sight depths. We find systematic offsets between dust mass surface densities (Sigma D) derived from extinction versus far-IR emission in both galaxies, with Sigma D,FIR/Sigma D,AV ratios ranging from 0.6-1.8. This work provides the highest-resolution dust extinction maps in SMC and LMC to date, which offer a vital independent benchmark for constraining dust emissivity, CO-dark gas fractions, and the multiscale structure of the ISM in low-metallicity environments.

We present a catalog of individual stellar and dust extinction properties along close to 500,000 sight lines in the southwest bar of the Small Magellanic Cloud (SMC). The catalog is based on multiband Hubble Space Telescope photometric data spanning near-ultraviolet to near-infrared wavelengths from the Small Magellanic Cloud Investigation of Dust and Gas Evolution survey (SMIDGE) covering a 100 x 200 pc area. We use the probabilistic technique of the Bayesian Extinction And Stellar Tool (BEAST) to model the spectral energy distributions of individual stars in SMIDGE and include the effects of observational uncertainties in the data. We compare BEAST-derived dust extinction properties with tracers of the interstellar medium, such as the emission from the 12CO (2-1) transition (I(CO)), the dust mass surface density (Sigma dust) from far-IR emission, the H i column density (N(H i)) from the 21 cm transition, and the mass fraction of polycyclic aromatic hydrocarbons (PAHs; q PAH, derived from IR emission). We find that the dust extinction (A(V)) in the SMIDGE field is strongly correlated with Sigma dust and I(CO), and less so with N(H i) and q PAH, and suggest potential explanations. Our extinction measurements are also sensitive to the presence of the 2175 & Aring; bump in the extinction curve toward UV bright stars. While most do not show evidence for the bump, we identify similar to 200 lines of sight that are 2175 & Aring; bump candidates. Furthermore, we find distinct structures in the dust extinction-distance distributions that provide insights into the 3D geometry of the SMC.

By analyzing the spectral energy distributions (SEDs) of resolved stars in nearby galaxies, we can constrain their stellar properties and line-of-sight dust extinction. From the Scylla survey, we obtain ultraviolet to near-infrared photometry from Wide Field Camera 3 on board the Hubble Space Telescope for more than 1.5 million stars in the SMC and LMC. We use the Bayesian Extinction and Stellar Tool (BEAST) to analyze the multiband SEDs of these sources and characterize their initial masses, ages, metallicities, distances, and line-of-sight extinction properties (e.g., A _V , R _V ). We apply quality cuts and perform validation simulations to construct a catalog of over 550,000 stars with high-reliability SED fits, which we use to analyze the stellar content and extinction properties of the SMC and LMC. We detect stars with masses as low as 0.6 M _⊙ . BEAST stellar age distributions show a jump in observed stars around 6 Gyr ago, which agrees with star formation histories. Extinctions ( A _V ) in both galaxies follow a log-normal distribution. We compare A _V with ancillary gas and dust tracers like H i , H α , and far-infrared (FIR) dust emission and find positive correlations on a field-by-field basis. We convert observed A _V to predicted dust surface densities using the Draine et al. model and find A _V -based dust surface densities are a factor of ∼2.5 lower than observed FIR-based dust surface densities, a correction factor similar to other studies.

The Panchromatic Hubble Andromeda Southern Treasury (PHAST) is a large 195-orbit Hubble Space Telescope program imaging ∼0.45 deg 2 of the southern half of M31's star-forming disk at optical and near-ultraviolet (NUV) wavelengths. The PHAST survey area extends the northern coverage of the Panchromatic Hubble Andromeda Treasury (PHAT) down to the southern half of M31, covering out to a radius of ∼13 kpc along the southern major axis and in total ∼two-thirds of M31's star-forming disk. This new legacy imaging yields stellar photometry of over 90 million resolved stars using the Advanced Camera for Surveys in the optical (F475W and F814W), and the Wide Field Camera 3 (WFC3) in the NUV (F275W and F336W). The photometry is derived using all overlapping exposures across all bands, and achieves a 50% completeness-limited depth of F475W ∼ 27.7 in the lowest surface density regions of the outer disk and F475W ∼ 26.0 in the most crowded, high surface brightness regions near M31's bulge. We provide extensive analysis of the data quality, including artificial star tests to quantify completeness, photometric uncertainties, and flux biases, all of which vary due to the background source density and the number of overlapping exposures. We also present seamless population maps of the entire M31 disk, which show relatively well-mixed distributions for stellar populations older than 1–2 Gyr, and highly structured distributions for younger populations. The combined PHAST + PHAT photometry catalog of ∼0.2 billion stars is the largest ever produced for equidistant sources and is available for public download by the community.

Using the Hubble Space Telescope/Space Telescope Imaging Spectrograph, ultraviolet (UV) extinction curves have been measured in M31 along 13 new sight lines, increasing the M31 sample to 17. This sample covers a wide area of M31, having galactocentric distances of 5–16 kpc, enabling the analysis of UV extinction curve variations over a large region of an external galaxy similar to the Milky Way with global galactic characteristics such as metallicity for the first time. No correlation is found between the extinction parameters and galactocentric distance, which might be expected if there is a radial metallicity gradient in M31. Most of the new UV extinction curves presented here are significantly different from the average extinction curves of the Milky Way, Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC), but the average M31 extinction curve is similar to the average extinction curve in the 30 Dor region of the LMC. The wide range of extinction curves seen in each individual Local Group galaxy suggests that global galactic properties such as metallicity may be less important than the local environmental conditions, such as density, UV radiation field, and shocks along each sight line. The combined behavior of the Milky Way, LMC, SMC, and now M31 UV extinction curves supports the idea that there is a family of curves in the Local Group with overlapping dust grain properties between different galaxies.

We use the Milky Way neutral hydrogen (HI) absorption and emission spectra from the Galactic Australian Square Kilometre Array Pathfinder (GASKAP) Phase II Pilot survey along with toy models to investigate the effects of stacking multicomponent spectra on measurements of peak optical depth and spin temperature. Shifting spectra by the peak in emission, 'primary' components shifted to 0 km s$^{-1}$ are correctly averaged. Additional components on individual sightlines are averaged with non-centred velocities, producing a broader and shallower 'secondary' component in the resulting stack. Peak optical depths and brightness temperatures of the secondary components from stacks are lower limits of their true average values due to the velocity offset of each component. The spin temperature however is well correlated with the truth since the velocity offset of components affects the emission and absorption spectra equally. Stacking 462 GASKAP absorption-emission spectral pairs, we detect a component with a spin temperature of 1320 $\pm$ 263 K, consistent with gas from the unstable neutral medium and higher than any previous GASKAP detection in this region. We also stack 2240 pilot survey spectra containing no Milky Way absorption, revealing a primary narrow and secondary broad component, with spin temperatures belonging to the cold neutral medium (CNM). Spatially binning and stacking the non-detections across the plane-of-sky by their distance from CNM absorption detections, the primary component's optical depth decreases with distance from known locations of cold gas. The spin temperature however remains stable in both components, over an approximate physical plane-of-sky distance of $\sim$ 100 pc.

We present a comparative analysis of interstellar hydrogen (HI) and potassium (KI) absorption from the radio and optical surveys, GASKAP and GALAH, to study the physical and kinematic properties of the cold interstellar medium (ISM) in the Milky Way foreground towards the Magellanic Clouds. By comparing GASKAP HI absorption with interstellar KI absorption detected in GALAH spectra of nearby stars (within 12 arcmin angular distance or a spatial separation of 0.75 pc), we reveal a strong kinematic correlation between these two tracers of the cold neutral ISM. The velocity offsets between matched HI and KI absorption components are small, with a mean (median) offset of -1.3 (-1.2) km s-1 and a standard deviation of 2.3 km s-1. The high degree of kinematic consistency suggests a close spatial association between Ki and cold HI gas. Correlation analyses reveal a moderate positive relationship between HI and KI line-of-sight properties, such as KI column density with HI column density or HI brightness temperature. We observe a 63

We present the Local Group L -Band Survey, a Karl G. Jansky Very Large Array (VLA) survey producing the highest-quality 21 cm and 1–2 GHz radio continuum images to date, for the six VLA-accessible, star-forming, Local Group galaxies. Leveraging the VLA’s spectral multiplexing power, we simultaneously survey the 21 cm line at high 0.4 km s ^−1 velocity resolution, the 1–2 GHz polarized continuum, and four OH lines. For the massive spiral M31, the dwarf spiral M33, and the dwarf irregular galaxies NGC 6822, IC 10, IC 1613, and the Wolf–Lundmark–Melotte Galaxy, we use all four VLA configurations and the Green Bank Telescope to reach angular resolutions of <5″ (10–20 pc) for the 21 cm line with <10 ^20 cm ^−2 column density sensitivity, and even sharper views (<2″; 5–10 pc) of the continuum. Targeting these nearby galaxies ( D ≲ 1 Mpc) reveals a sharp, resolved view of the atomic gas, including 21 cm absorption, and continuum emission from supernova remnants and H ii regions. These data sets can be used to test theories of the abundance and formation of cold clouds, the driving and dissipation of interstellar turbulence, and the impact of feedback from massive stars and supernovae. Here, we describe the survey design and execution, scientific motivation, data processing, and quality assurance. We provide a first look at and publicly release the wide-field 21 cm H i data products for M31, M33, and four dwarf irregular targets in the survey, which represent some of the highest-physical-resolution 21 cm observations of any external galaxies beyond the LMC and SMC.

Cold neutral hydrogen (H i ) is a crucial precursor for molecular gas formation and can be studied via H i absorption. This study investigates H i absorption in low column density regions of the Small and Large Magellanic Clouds (SMC and LMC) using the Galactic-ASKAP H i (GASKAP-H i ) survey, conducted by the Australian Square Kilometer Array Pathfinder (ASKAP). We select 10 SMC directions in the outer regions and 18 LMC directions, with four in the outskirts and 14 within the main disk. Using the radiative transfer method, we decompose the emission and absorption spectra into individual cold neutral medium (CNM) and warm neutral medium (WNM) components. In the SMC, we find H i peak optical depths of 0.09–1.16, spin temperatures of ∼20–50 K, and CNM fractions of 1%–11%. In the LMC, optical depths range from 0.03–3.55, spin temperatures from ∼10–100 K, and CNM fractions from 1%–100%. The SMC’s low CNM fractions likely result from its low metallicity and large LOS depth. Additionally, the SMC’s outskirts show lower CNM fractions than the main body, potentially due to increased CNM evaporation influenced by the hot Magellanic Corona. Shell motions dominate the kinematics of the majority of CNM clouds in this study and likely supply cold H i to the Magellanic Stream. In the LMC, high CNM fraction clouds are found near supergiant shells, where thermal instability induced by stellar feedback promotes WNM-to-CNM transition. Although no carbon monoxide has been detected, enhanced dust shielding in these areas helps maintain the cold H i .

Carbon plays key roles in the interstellar medium (ISM)—as a constituent of dust, as the carrier of the dominant far-infrared (FIR) cooling line, and as a component of various important molecules. But despite this, there are very few measurements of the abundance and depletion of carbon in the diffuse ISM. As with other elements, these measurements are traditionally performed in the ultraviolet. But for carbon, such measurements are extremely difficult, and fewer than 20 have been reported in the literature to date. Here, we present a novel method of measuring the abundance and depletion of carbon in the diffuse ISM: by observing absorption of the 158 μ m [C ii ] line in the FIR. We present a catalog of 432 candidate sightlines that use bright nearby galaxies as background sources, and predict the [C ii ] absorption expected toward each. We conducted a pilot study using SOFIA, targeting sightlines toward the galaxies IC 342 and Circinus. We report a potential detection of Galactic [C ii ] absorption along the IC 342 sightline, although it requires disentangling [C ii ] emission from IC 342 itself. The Circinus sightline had an insufficiently stable instrumental baseline to allow a detection. This SOFIA study informs the prospects for [C ii ] absorption measurements with future facilities. To that end, we explore the potential for four proposed future FIR telescopes—PRIMA, FIRSST, SALTUS, and Origins—to detect [C ii ] absorption. We find that all four facilities would be able to detect [C ii ] absorption along a significant number of sightlines.

We present a gas phase decomposition of the deep 21 cm H I spectrum of the target PKS1934-638 observed by the Australia Telescope Compact Array. Our measurements achieve sigma(tau) = 5.9x 10(-4) making this one of the deepest 21 cm H I absorption spectra to date. Using the GaussPy package, we conducted a two phase Gaussian decomposition on the absorption spectrum measured on target and the associated GASS emission spectra at varying angular offsets. The spectral pairs were decomposed independently and permuted through all possible line-of-sight configurations to determine a weighted solution set of Gaussian components. Of the components derived, we identify two candidates in absorption that are likely unstable or warm, with spin temperatures T-s = 1300 +/- 100K, 680 +/- 70K. Cumulatively, these features represent a mass fraction of f(UNM) = 0.59 +/- 0.22 which is higher than has typically been reported. We also detect a component in emission only, with a possible detection of absorption, at T-k,T-max = 7610 +/- 65K. The UNM is typically difficult to detect in absorption due to it's low optical depth, our results would make the detections among the few examples currently known. We believe our high mass fraction is attributable to the high optical depth sensitivity of our observations allowing marginal warm gas detections in absorption to come into prominence, and possibly also an atypical line of sight.