An ATCA Survey of HI Absorption in the Magellanic Clouds I: HI Gas Temperature Measurements in the Small Magellanic Cloud. (arXiv:1908.04787v1 [astro-ph.GA])

An ATCA Survey of HI Absorption in the Magellanic Clouds I: HI Gas Temperature Measurements in the Small Magellanic Cloud. (arXiv:1908.04787v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Jameson_K/0/1/0/all/0/1">Katherine Jameson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McClure_Griffiths_N/0/1/0/all/0/1">Naomi McClure-Griffiths</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_B/0/1/0/all/0/1">Boyang Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dickey_J/0/1/0/all/0/1">John Dickey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Staveley_Smith_L/0/1/0/all/0/1">Lister Staveley-Smith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stanimirovic_S/0/1/0/all/0/1">Snezana Stanimirovic</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dempsey_J/0/1/0/all/0/1">James Dempsey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dawson_J/0/1/0/all/0/1">Joanne Dawson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Denes_H/0/1/0/all/0/1">Helga Denes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bolatto_A/0/1/0/all/0/1">Alberto Bolatto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Li_D/0/1/0/all/0/1">Di Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wong_T/0/1/0/all/0/1">Tony Wong</a>

We present the first results from the Small Magellanic Cloud portion of a new
Australia Telescope Compact Array (ATCA) HI absorption survey of both of the
Magellanic Clouds, comprising over 800 hours of observations. Our new HI
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 HI
absorption; from this we measure a column density weighted mean average spin
temperature of $=150$ 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 $sim{30}$ K for this
sample, lower than the average of $sim{40}$ K in the Milky Way. The HI 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 ($N_{text{HI}}>2times{10^{21}}$ cm$^{-2}$). The optical depth and
temperature of the cold neutral atomic gas shows no strong trend with location
spatially or in velocity. Despite the low metallicity environment, we find an
average cold gas fraction of $sim{20%}$, not dissimilar from that of the
Milky Way.

We present the first results from the Small Magellanic Cloud portion of a new
Australia Telescope Compact Array (ATCA) HI absorption survey of both of the
Magellanic Clouds, comprising over 800 hours of observations. Our new HI
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 HI
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 $sim{30}$ K for this
sample, lower than the average of $sim{40}$ K in the Milky Way. The HI 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 ($N_{text{HI}}>2times{10^{21}}$ cm$^{-2}$). The optical depth and
temperature of the cold neutral atomic gas shows no strong trend with location
spatially or in velocity. Despite the low metallicity environment, we find an
average cold gas fraction of $sim{20%}$, not dissimilar from that of the
Milky Way.

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