28th of March 2018 |
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ATNF Colloquium |
Gas and Star Formation at Low Metallicity in the Magellanic Clouds |
by Katie Jameson (ANU) |
The Magellanic Clouds are two
interacting, gas-rich, star-forming, low-mass, nearby satellite
galaxies of the Milky Way that afford a unique view of low-metallicty
star-forming regions, providing the nearest laboratories to study the
processes relevant to star formation in the early universe. We use the
dust emission from HERITAGE Herschel data (Meixner et al. 2013) to map
the molecular gas in the Magellanic Clouds, avoiding the known biases
of CO emission as a tracer of H2, and find that on large scales the
molecular gas depletion time is not a strong function of
metallicity. We compare galaxy-scale analytic star formation models to
our observations and find that successfully predicting the trends in
the low metallicity environment needs the inclusion of a diffuse
neutral medium. The averaging of the scatter in the molecular gas
depletion time as a function of scale size suggests that the drivers
of the star formation process in these galaxies operate on large
scales. On small (~ few pc) scales in the Small Magellanic Cloud
(SMC), we study the effect of metallicity on the structure of
photodissociation regions in the outskirts of molecular clouds using
[CII] and [OI] spectroscopy combined with new ALMA 7-m array maps of
12CO and 13CO. We estimate the total amount of molecular gas using
[CII] to trace H2 at low-Av and 12CO to trace H2 at high-Av. We find
that most of the molecular gas is traced by [CII] emission and that
metallicity only affects the relationship between CO emission and
molecular gas through changes in Av. Using mid-infrared spectroscopy
from Spitzer Space Telescope in the SMC (Sandstrom et al. 2012), we
model the H2 rotational line emission to estimate temperatures, column
densities, and fractions of warm H2 gas (T>100 K). The temperatures
and column densities of warm H2 gas are similar to nearby galaxies,
but the SMC shows somewhat high fractions of warm H2. The properties
of the warm H2 gas indicate that it is located in photodissociation
regions that are more extended in the low metallicity environment of
the SMC. Finally, I will discuss our new ATCA survey of HI and OH
absorption in the Magellanic Clouds.
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