Statistics
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...208.4914h&link_type=abstract
American Astronomical Society Meeting 208, #49.14; Bulletin of the American Astronomical Society, Vol. 38, p.126
Statistics
Scientific paper
We report our findings on the volume densities of H2 in Giant Molecular Clouds (GMCs) associated with photodissociation regions (PDRs) in the nearby galaxies M81 and M83. In many instances, patches of HI are found close to bright FUV sources, as is expected for PDRs. The detected PDRs, in which dissociating photons dominate the radiation field, are larger than presently-well-studied PDRs in the Galaxy and have sizes of 100 parsec. The complexes of young, hot stars giving rise to these PDRs create a 'blanket' of photodissociated HI.The balance equation governing the photodissociation process needs the ultraviolet luminosity incident on the surface of the GMC and the local dust-to-gas ratio together with the HI column density in order to calculate the volume density of molecular hydrogen. Previous work by Smith et al. (2001) on M101 has shown that the GMCs in that galaxy have volume densities of 102 cm-3, similar to GMCs our own Galaxy.As PAHs are also thought to trace star formation, and their MIR emission comes mostly from PDRs, we use this property to confirm the presence of PDRs near FUV sources. We present the statistics of this comparison and our findings as to what extent we are really seeing large scale PDRs in nearby galaxies.We outline our plans to extend this work in the coming year, including progress on our current work on M33.We used recent radio data kindly provided by the THINGS group, David Thilker and Robert Braun, Galex UV data and Spitzer IRAC data.This work is funded by STScI's Director's Discretionary Research Fund.
Allen Rosalind J.
Heiner Jonathan S.
van der Kruit Pieter Corijnus
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