An ATCA Survey of H I Absorption in the Magellanic Clouds. I. H I Gas Temperature Measurements in the Small Magellanic Cloud
Abstract
We present the first results from the Small Magellanic Cloud portion of a new Australia Telescope Compact Array H I absorption survey of both of the Magellanic Clouds, comprising over 800 hr of observations. Our new H I absorption line data allow us to measure the temperature and fraction of cold neutral gas in a low-metallicity environment. We observed 22 separate fields, targeting a total of 55 continuum sources, against 37 of which we detected H I absorption; from this we measure a column-density-weighted mean average spin temperature of < {T}{{s}}> = 150 K. Splitting the spectra into individual absorption line features, we estimate the temperatures of different gas components and find an average cold gas temperature of ∼30 K for this sample, lower than the average of ∼40 K in the Milky Way. The H I appears to be evenly distributed throughout the SMC, and we detect absorption in 67% of the lines of sight in our sample, including some outside the main body of the galaxy (N H I > 2× {10}21 cm-2). The optical depth and temperature of the cold neutral atomic gas show no strong trend with location spatially or in velocity. Despite the low-metallicity environment, we find an average cold gas fraction of ∼20%, not dissimilar from that of the Milky Way.
- Publication:
-
The Astrophysical Journal Supplement Series
- Pub Date:
- September 2019
- DOI:
- 10.3847/1538-4365/ab3576
- arXiv:
- arXiv:1908.04787
- Bibcode:
- 2019ApJS..244....7J
- Keywords:
-
- galaxies: ISM;
- ISM: clouds;
- Magellanic Clouds;
- radio lines: ISM;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 22 pages, 16 figures, accepted for publication in ApJS