An ATCA Survey of H I Absorption in the Magellanic Clouds. I. H I Gas Temperature Measurements in the Small Magellanic Cloud

Katherine E. Jameson, N. M. McClure-Griffiths, Boyang Liu, John M. Dickey, Lister Staveley-Smith, Snežana Stanimirović, James Dempsey, J. R. Dawson, Helga Dénes, Alberto D. Bolatto, Di Li, Tony Wong

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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.
Original languageEnglish
Pages (from-to)7
JournalThe Astrophysical Journal Supplement Series
Volume244
Issue number1
DOIs
Publication statusPublished - 1 Sept 2019

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