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

Nickolas M. Pingel; Hongxing Chen; Snežana Stanimirović; Eric W. Koch; Adam K. Leroy; Erik Rosolowsky; Chang-Goo Kim; Julianne J. Dalcanton; Fabian Walter; Michael P. Busch; Ryan Chown; Jennifer Donovan Meyer; Cosima Eibensteiner; Deidre A. Hunter; Sumit K. Sarbadhicary; Elizabeth Tarantino; Vicente Villanueva; Thomas G. Williams

doi:10.3847/1538-4357/ad6604

The Astrophysical Journal (Jan 2024)

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

Nickolas M. Pingel,
Hongxing Chen,
Snežana Stanimirović,
Eric W. Koch,
Adam K. Leroy,
Erik Rosolowsky,
Chang-Goo Kim,
Julianne J. Dalcanton,
Fabian Walter,
Michael P. Busch,
Ryan Chown,
Jennifer Donovan Meyer,
Cosima Eibensteiner,
Deidre A. Hunter,
Sumit K. Sarbadhicary,
Elizabeth Tarantino,
Vicente Villanueva,
Thomas G. Williams

Affiliations

Nickolas M. Pingel: ORCiD; University of Wisconsin-Madison , Department of Astronomy, 475 N Charter St, Madison, WI 53703, USA ; [email protected]
Hongxing Chen: ORCiD; University of Wisconsin-Madison , Department of Astronomy, 475 N Charter St, Madison, WI 53703, USA ; [email protected]
Snežana Stanimirović: ORCiD; University of Wisconsin-Madison , Department of Astronomy, 475 N Charter St, Madison, WI 53703, USA ; [email protected]
Eric W. Koch: ORCiD; Center for Astrophysics ∣ Harvard & Smithsonian , 60 Garden St., 02138 Cambridge, MA, USA
Adam K. Leroy: ORCiD; Department of Physics, The Ohio State University , Columbus, Ohio 43210, USA; Center for Cosmology & Astro-Particle Physics, The Ohio State University , Columbus, Ohio 43210, USA
Erik Rosolowsky: ORCiD; Dept. of Physics, University of Alberta , 4-183 CCIS, Edmonton, Alberta, T6G 2E1, Canada
Chang-Goo Kim: ORCiD; Department of Astrophysical Sciences, Princeton University , 4 Ivy Lane, Princeton, NJ 0844, USA
Julianne J. Dalcanton: ORCiD; Center for Computational Astrophysics, Flatiron Institute , 162 Fifth Avenue, New York, NY 10010, USA; Department of Astronomy, Box 351580, University of Washington , Seattle, WA 98195, USA
Fabian Walter: ORCiD; Max-Planck-Institut für Astronomie , Königstuhl 17, 69117 Heidelberg, Germany
Michael P. Busch: ORCiD; Department of Astronomy & Astrophysics, University of California , San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
Ryan Chown: ORCiD; Department of Physics, The Ohio State University , Columbus, Ohio 43210, USA; Center for Cosmology & Astro-Particle Physics, The Ohio State University , Columbus, Ohio 43210, USA
Jennifer Donovan Meyer: ORCiD; National Radio Astronomy Observatory , 520 Edgemont Rd., Charlottesville, VA 22968, USA
Cosima Eibensteiner: ORCiD; National Radio Astronomy Observatory , 520 Edgemont Rd., Charlottesville, VA 22968, USA
Deidre A. Hunter: ORCiD; Lowell Observatory , 1400 W Mars Hill Road, Flagstaff, AZ 86001, USA
Sumit K. Sarbadhicary: ORCiD; Department of Physics, The Ohio State University , Columbus, Ohio 43210, USA; Center for Cosmology & Astro-Particle Physics, The Ohio State University , Columbus, Ohio 43210, USA
Elizabeth Tarantino: ORCiD; Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA
Vicente Villanueva: ORCiD; Departamento de Astronomía, Universidad de Concepción , Barrio Universitario, Concepción, Chile
Thomas G. Williams: ORCiD; Sub-department of Astrophysics, Department of Physics, University of Oxford , Keble Road, Oxford, OX1 3RH, UK

DOI: https://doi.org/10.3847/1538-4357/ad6604
Journal volume & issue: Vol. 974, no. 1
p. 93

Abstract

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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.

Published in The Astrophysical Journal

ISSN: 1538-4357 (Online)
Publisher: IOP Publishing
Country of publisher: United Kingdom
LCC subjects: Science: Astronomy: Astrophysics
Website: https://iopscience.iop.org/journal/0004-637X

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