TY - JOUR
T1 - An ATCA Survey of H I Absorption in the Magellanic Clouds. I. H I Gas Temperature Measurements in the Small Magellanic Cloud
AU - Jameson, Katherine E.
AU - McClure-Griffiths, N. M.
AU - Liu, Boyang
AU - Dickey, John M.
AU - Staveley-Smith, Lister
AU - Stanimirović, Snežana
AU - Dempsey, James
AU - Dawson, J. R.
AU - Dénes, Helga
AU - Bolatto, Alberto D.
AU - Li, Di
AU - Wong, Tony
PY - 2019/9/1
Y1 - 2019/9/1
N2 - 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.
AB - 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.
KW - galaxies: ISM
KW - ISM: clouds
KW - Magellanic Clouds
KW - radio lines: ISM
U2 - 10.3847/1538-4365/ab3576
DO - 10.3847/1538-4365/ab3576
M3 - Article
SN - 0067-0049
VL - 244
SP - 7
JO - The Astrophysical Journal Supplement Series
JF - The Astrophysical Journal Supplement Series
IS - 1
ER -