Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21812901r&link_type=abstract
American Astronomical Society, AAS Meeting #218, #129.01; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
In the past 15 years, there has been considerable effort to estimate the mass of H2 from dust FIR measurements in order to constrain the star formation law in low metallcity galaxies, where the low dust abundance and subsequent lack of shielding from ambient radiation makes photo-dissociated CO an ineffective tracer of molecular gas. This method relies on an estimate of the gas-to-dust ratio (GDR) from gas H I 21 cm, CO, and dust FIR observations either in diffuse regions where no H2 is expected to exist, or in the densest regions where CO is known to trace H2 and the value of the X factor can be derived simultaneously with the GDR. Thus, the GDR is assumed to be independent of local environment and density. In reality, dust destruction by shocks in the diffuse ISM, mantling in the dense ISM, and variations in the dust production rate with star formation activity can lead to significant (factor 2-3) variations in the GDR and bias this estimate of the H2 mass. In addition, the dust emissivity is assumed to be constant, although it actually depends on density because grain growth in dense molecular clouds increases the emissivity by a factor of a few. Here, we investigate systematic variations of the GDR, dust emissivity, and X factor with column density, radiation field, and star formation activity based on the correlation between gas mass derived from CO and H I 21 cm observations and FIR emission from the HERschel Inventory of The Agents of Galactic Evolution (HERITAGE) project in the Magellanic Clouds. We show that the dust-gas correlation cannot be explained by a single GDR, dust emissivity, or X factor, and we use a simple model of GDR and dust emissivity variations with column density of explain the observed trends.
Gordon Karl Douglas
HERITAGE
Meixner Matthew
Roman-Duval Julia
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