Other
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21711203c&link_type=abstract
American Astronomical Society, AAS Meeting #217, #112.03; Bulletin of the American Astronomical Society, Vol. 43, 2011
Other
Scientific paper
Dust emission in the mid-infrared (MIR), mainly from polycyclic aromatic hydrocarbons (PAHs), is used as a star formation rate tracer at both low and high-redshifts. However, PAHs can be excited not only by young UV-emitting stars, but also by the softer radiation field of older stars. Yet no study quantifying the fraction and spatial distribution of this 'diffuse' MIR component has been performed. To do this, we compare the Spitzer 8 micron emission (stellar subtracted) to the distribution of the Hα recombination line in a sample of SINGS spiral galaxies. Dust-corrected Hα emission accurately traces star formation as only hot young stars can produce the required ionizing continuum (outside of the immediate environs of an AGN or strong shocks). The 8 micron and Hα images show qualitative differences, with the Hα appearing much more limited to clumpy HII regions and the 8 micron having a smoother appearance (after convolution to the same resolution). Considering only diffuse regions (i.e. ignoring HIIphot-identified HII regions), we see that the diffuse/total 8 micron emission ratio is significantly greater than the diffuse/total Hα emission ratio. This difference implies that some of the PAH excitation in normal star-forming spiral galaxies is due to older stars (20% in the first galaxy analyzed, NGC 628). Applying identical techniques to the good-resolution FIR Herschel data on a similar sample of galaxies will provide an estimate of the FIR dust emission attributable to diffuse heating.
Calzetti Daniela
Crocker Alison Faye
KINGFISH Team
Thilker David A.
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