Large-Scale Photodissociation Regions in Nearby Spiral Galaxies
Jonathan Heiner
Université Laval
Star formation in galaxies is driven by the presence of molecular gas,
but detecting that gas is difficult if the density and temperature are
too low. Using a method of combining high-resolution HI and Far-UV data,
along with gas metallicity data, large-scale photodissociation regions
(PDRs) can be identified near areas of active star formation. These data
can be used to derive total hydrogen densities in the associated giant
molecular clouds (GMCs).
Central to this method is the use of atomic hydrogen produced in the
PDRs, combined with careful calculations of the UV radiation field. The
atomic hydrogen is seen surrounding bright FUV sources, as is expected
in PDRs. The size of these large scale PDRs is typically of the order of
100 parsec.
Combining results from M81, M83, and M33 provides a comprehensive
overview of candidate PDRs in these nearby spiral galaxies and their
properties. In M33 especially, the connection to CO emission and to PAH
emission was analyzed in order to test the PDR model in more detail, at
scales as small as 30 pc. Densities of the PDRs are found to be similar
across the three galaxies, despite apparent local differences in gas
content. There is a statistical correspondence between GMCs with high
molecular density and the presence of detectable CO emission.
Date: | Jeudi, le 17 septembre 2009 |
Heure: | 11:30 |
Lieu: | Université de Montréal |
| Pavillon Roger-Gaudry, Local D-460 |
Contact: | Pierre Bergeron |
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