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Measuring the properties of the cold neutral medium (CNM) in low-metallicity galaxies provides insight into heating and cooling mechanisms in early Universe-like environments. We report detections of two localized atomic neutral hydrogen (HI) absorption features in NGC 6822, a low-metallicity (0. 2 Z_) dwarf galaxy in the Local Group. These are the first unambiguous CNM detections in a low-metallicity dwarf galaxy outside the Magellanic Clouds. The Local Group L-Band Survey (LGLBS) enabled these detections due to its high spatial (15 pc for HI emission) and spectral (0. 4) resolution. We introduce LGLBS and describe a custom pipeline to search for HI absorption at high angular resolution and extract associated HI emission. A detailed Gaussian decomposition and radiative transfer analysis of the NGC 6822 detections reveals five CNM components, with key properties: a mean spin temperature of 326 K, a mean CNM column density of 3. 110^20 cm^-2, and CNM mass fractions of 0. 33 and 0. 12 for the two sightlines. Stacking non-detections does not reveal low-level signals below our median optical depth sensitivity of 0. 05. One detection intercepts a star-forming region, with the HI absorption profile encompassing the CO (2-1) emission, indicating coincident molecular gas and a depression in high-resolution HI emission. We also analyze a nearby sightline with deep, narrow HI self-absorption dips, where the background warm neutral medium is attenuated by intervening CNM. The association of CNM, CO, and H emissions suggests a close link between the colder, denser HI phase and star formation in NGC 6822.
Pingel et al. (Thu,) studied this question.