Loading…

The Local Group L-band Survey: The First Measurements of Localized Cold Neutral Medium Properties in the Low-metallicity Dwarf Galaxy NGC 6822

Measuring the properties of the cold neutral medium (CNM) in low-metallicity galaxies provides insights into heating and cooling mechanisms in early Universe-like environments. We report detections of two localized atomic neutral hydrogen (H i ) absorption features in NGC 6822, a low-metallicity (0....

Full description

Saved in:
Bibliographic Details
Published in:The Astrophysical journal 2024-10, Vol.974 (1), p.93
Main Authors: Pingel, Nickolas M., Chen, Hongxing, Stanimirović, Snežana, Koch, Eric W., Leroy, Adam K., Rosolowsky, Erik, Kim, Chang-Goo, Dalcanton, Julianne J., Walter, Fabian, Busch, Michael P., Chown, Ryan, Donovan Meyer, Jennifer, Eibensteiner, Cosima, Hunter, Deidre A., Sarbadhicary, Sumit K., Tarantino, Elizabeth, Villanueva, Vicente, Williams, Thomas G.
Format: Article
Language:English
Subjects:
Citations: Items that this one cites
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Measuring the properties of the cold neutral medium (CNM) in low-metallicity galaxies provides insights into heating and cooling mechanisms in early Universe-like environments. We report detections of two localized atomic neutral hydrogen (H i ) 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 H i emission) and spectral (0.4 km s −1 ) resolution. We introduce LGLBS and describe a custom pipeline for searching for H i absorption at high angular resolution and extracting associated H i 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 32 ± 6 K, a mean CNM column density of 3.1 × 10 20 cm −2 , and CNM mass fractions of 0.33 and 0.12 for the two sightlines. Stacking nondetections does not reveal low-level signals below our median optical depth sensitivity of 0.05. One detection intercepts a star-forming region, with the H i absorption profile encompassing the CO (2−1) emission, indicating coincident molecular gas and a depression in high-resolution H i emission. We also analyze a nearby sightline with deep, narrow H i self-absorption dips, where the background warm neutral medium is attenuated by intervening CNM. The association of CNM, CO, and H α emissions suggests a close link between the colder, denser H i phase and star formation in NGC 6822.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ad6604