Nickolas M. Pingel

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.

Wide-field spectral-line imaging with modern radio interferometers remains challenging when the emission is extended, multiscale, and distributed over many overlapping pointings. In this regime, accurate reconstruction requires a joint treatment of the calibrated visibilities, control of image-domain regularity, and, when necessary, recovery of missing short spacings from single-dish data. We present IViS (Interferometric Visibility-domain Inversion Software), a GPU-accelerated Python framework for visibility-domain joint deconvolution, and assess its performance for wide-field H I imaging with the Australian Square Kilometre Array Pathfinder (ASKAP). The current model, Classic3D , reconstructs a nonparametric sky cube directly from calibrated visibilities by minimizing a regularized least-squares criterion. The forward model relies on a nonuniform fast Fourier transform (NUFFT), supports joint deconvolution across all mosaic pointings, and allows positivity constraints through bounded optimization. Short-spacing information can be incorporated through a fusion term that models single-dish data from the same sky estimate. We validate the method using synthetic point-source, noise-only, and multiscale diffuse-emission simulations, and apply it to ASKAP full-survey observations toward the Large Magellanic Cloud (LMC). The simulations show that IViS recovers point-source flux accurately in the absence of regularization and that the regularization strength sets the trade-off between noise suppression and effective resolution. Relative to linear mosaicking of independently deconvolved pointings, joint deconvolution can recover more large-scale power. When single-dish information is included, the reconstructed power spectra closely reproduce the input sky statistics over a broad range of spatial frequencies. Applied to ASKAP data, IViS yields 10 h mosaics with an effective resolution of 22″ of Galactic foreground emission and LMC emission with reduced residual side-lobe structure and realistic multiscale morphology. A comparison with ASKAPSoft using multiscale CLEAN shows that, for this specific target and a single observing block, Classic3D exhibits fewer residual side-lobes and recovers substantially more power at low spatial frequencies. IViS provides a flexible visibility-domain framework for joint deconvolution of large spectral-line mosaics, and illustrates the potential of regularized inverse-problem approaches as an alternative to traditional CLEAN-based imaging for next-generation radio surveys.

Diffuse H i emission in the circumgalactic medium (CGM) of NGC 891 and NGC 4565 has been previously shown to trace an inflow along minor axis pointings and to corotate with the H i disk along major axis pointings out to ≈100 kpc. To obtain a 360 ^∘ view of the inner neutral CGM (∘ between the principal axes, achieving a 5 σ column density sensitivity of 1.1–1.2 × 10 ¹⁷ cm ⁻² over a 20 km s ⁻¹ velocity width. While detecting H i emission in the inner CGM with single-dish telescopes is common, separating the true CGM emission from disk contamination is extremely challenging and has so far been largely unsuccessful. To achieve that, we compare our single-dish detections to deep interferometric maps from the Westerbork Synthesis Radio Telescope (WSRT) HALOGAS survey, and improve upon our previous methods by incorporating velocity offset corrections and channel-wise brightness temperature scaling. We find that 30%–38% and 18%–28% of the emission detected by the GBT cannot be explained by WSRT in NGC 891 and NGC 4565, respectively, implying a true CGM detection. There is 4–6 × (3–7×) more H i along the off-axes than major (minor) axes, nullifying the common assumption of azimuthal symmetry of the neutral CGM. The velocity profile of the diffuse inner CGM suggests a lagged corotation with the H i disk in both galaxies. This exercise illustrates the power of deep observation and careful cross-instrument comparisons to characterize the diffuse H i in the CGM.

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.

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.