Snežana Stanimirović

We use atomic hydrogen (H I ) absorption detections from the GASKAP-H I 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%) than in the Milky Way. We examine the connection between the CNM, molecular gas, and star formation, finding that CNM correlates more closely with molecular gas than WNM, while molecular gas shows a tighter relation with star formation. Molecular hydrogen (H ₂ ) formation begins near N _HI,CNM ∼ 10 ²⁰ cm ⁻² , and nearly all sightlines with N _HI,CNM > 10 ²¹ cm ⁻² contain molecular gas. The CNM fraction increases with visual extinction ( A _V ), and the LMC maintains CNM fractions comparable to those in the Milky Way at substantially lower A _V , likely due to higher local densities and a longer line-of-sight depth. Sightlines near expanding shells tend to show higher CNM fractions, although this is partly driven by higher total H I column densities. Finally, the CNM kinematics generally follow the H I disk rotation, with about 7% of components showing velocity offsets greater than 25 km s ⁻¹ , likely tracing inflows or outflows driven by stellar feedback or large-scale interactions within the Magellanic system.

Resolving atomic gas at ≲100 pc physical resolution is currently feasible only for the very nearest galaxies. We combine 120 pc resolution H i data using the Karl G. Jansky Very Large Array (VLA) from the first data release of the Local Group L -Band Survey (LGLBS) with uniformly processed infrared, ultraviolet, H α , and CO maps. We analyze the radial profiles of gas, stars, and recent star formation for six local galaxies: M31, M33, IC 10, IC 1613, NGC 6822, and Wolf–Lundmark–Melotte. Across the sample, atomic-gas disks are the most extended component, reaching r _HI = 2.8–5.8 kpc in the dwarfs and 13–26 kpc in M33 and M31. Azimuthally averaged Σ _atom profiles are often flat or only slowly declining compared to the steeper decline of Σ _⋆ and Σ _SFR , with outer H i scale lengths of l HI outer ≈ 1.0 –8.5 kpc. The mass-weighted H i surface densities on a 120 pc scale generally exceed the azimuthally averaged values by 10%–70%, showing that localized high-column-density atomic structures persist even where azimuthally averaged profiles appear smooth. Atomic-gas depletion times rise from τ dep atom ≈ 0.8 –17 Gyr within the stellar half-mass–radius to tens to 100 Gyr in the outer disks. Molecular depletion times are shorter. We provide a public release of these multiwavelength data, which provide a valuable reference for the LGLBS targets and also form the basis for a companion paper that relates star formation, gas phases, and midplane pressure on 120 pc scales.

We analyze H i 21 cm observations of the Local Group dwarf galaxy Wolf–Lundmark–Melotte (WLM) from the Local Group L -Band Survey to search for evidence of ram pressure stripping. While previous MeerKAT-16 observations of WLM showed evidence for off-galaxy atomic gas emission with a geometry suggestive of ram pressure stripping, our observations find no evidence for this stripped gas. We demonstrate that our observations would be sensitive to the claimed detections and suggest that an uncorrected observational flaw with the MeerKAT data led to the apparent off-galaxy emission. The lack of off-galaxy emission obviates the need for uncharacteristically high values of the density of the intergalactic medium in this region.

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 _⊙ stars) Wolf–Rayet stars (W-Rs; >30 M _⊙ 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 _⊙ 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.

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 (−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.

With the aim of evaluating the roles of the cold neutral medium (CNM) in the cloud-scale baryon cycle, we perform a high-resolution study of the CNM in and around the extreme star-forming region 30 Doradus (30 Dor). For our study, we use Galactic Australian Square Kilometre Array Pathfinder H i Survey data and produce H i emission and absorption cubes on 7 pc scales. To examine the CNM structures toward 30 Dor, we decompose the H i absorption cube into 862 Gaussian components and find that these components are distributed at four velocity ranges (B1, B2, B3, and B4, respectively): 200–230 km s ⁻¹ , 230–260 km s ⁻¹ , 260–277 km s ⁻¹ , and 277–300 km s ⁻¹ . We derive line-of-sight average spin temperatures and opacity-corrected total H i column densities and show that the B1–B4 structures have systematically different properties, indicating that they are physically distinct. As for the nature of the observed CNM structures, we find that B2 is associated with the main dense structure where ionized, atomic, and molecular gases are concentrated. B3 and B4 trace inflows whose combined mass flux rate of 0.14 M _⊙ yr ⁻¹ is comparable to the current star formation rate, while B1 probes outflows with a much lower mass flux rate of 0.007 M _⊙ yr ⁻¹ . Interestingly, the H i column densities in B1–B4 are nearly uniform with a factor of 2 spatial variations, implying the presence of H i shielding layers for H ₂ formation.

Turbulence in the interstellar medium (ISM) plays an important role in many physical processes, including forming stars and shaping complex ISM structures. In this work, we investigate the H i turbulence properties of the Small Magellanic Cloud (SMC) to reveal what physical mechanisms drive the turbulence and at what scales. Using high-resolution H i data from the Galactic ASKAP survey and multipoint structure functions (SFs), we perform a statistical analysis of H i turbulence in 34 subregions of the SMC. The two-point SFs tend to show a linear trend, and their slope values are relatively uniform across the SMC, suggesting that large-scale structures exist and are dominant in the two-point SFs. On the other hand, seven-point SFs enable us to probe small-scale turbulence by removing large-scale fluctuations, which is difficult to achieve with the two-point SFs. In the seven-point SFs, we find break features at scales of 34–84 pc, with a median scale of ∼50 pc. This result indicates the presence of small-scale turbulence fluctuations in the SMC and quantifies their scale. In addition, we find strong correlations between the slope values of the seven-point SFs and stellar-feedback-related quantities (e.g., H α intensity, the number of young stellar objects, and the number of H i shells), suggesting that stellar feedback may affect the small-scale turbulence properties of the H i gas in the SMC. Lastly, the estimated sonic Mach numbers across the SMC are subsonic, which is consistent with the fact that the H i gas of the SMC primarily consists of a warm neutral medium.