Dr. Bruce Draine
Princeton

University of Florida Astronomy Colloquium - Mar. 5th, 2008

Dust Masses, PAH Fractions, and Starlight Intensities in the SINGS Galaxies

Dust models have been used to reproduce the infrared and submm emission from 65 galaxies in the SINGS sample. It is found that the dust masses estimated from these models -- based on only the observed IR and submm emission -- correlate very well with the gas mass and metallicity. In most galaxies, the estimated dust mass is consistent with a substantial fraction of interstellar C, Mg, Si, and Fe being locked up in solid grains. The interstellar media in these galaxies evidently maintain a large fraction of their "refractory" elements in solid form.

The dust models also allow estimation of the PAH content of the galaxies. The fraction of the interstellar dust mass that is contributed by PAHs correlates with galaxy metallicity.

The dust modeling involves estimation of the distribution of starlight intensities in the galaxies. The dust-weighted starlight intensity U varies from galaxy to galaxy, with a median U=2.4 (in units of the starlight intensity in the local Milky Way). The dust models require that a fraction of the dust heating take place in regions of high starlight intensity, which are presumed to correlate with star-forming regions.

For nearby galaxies, the global modeling described above can be repeated on the 40 arcsec scale of the MIPS 160um psf, revealing variations in dust surface density, PAH fraction, and starlight intensity properties within galaxies.