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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 ⟨Ts⟩= 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 (NH I > 2 x 1021 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.
Bibliographical noteCopyright 2019 The American Astronomical Society. First published in the Astrophysical Journal Supplement Series, 244(1), 7, 2019, published by IOP Publishing. The original publication is available at https://doi.org/10.3847/1538-4365/ab3576. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.
- galaxies: ISM
- ISM: clouds
- Magellanic Clouds
- radio lines: ISM
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