QUANTIFYING NON-STAR-FORMATION-ASSOCIATED 8 {mu}m DUST EMISSION IN NGC 628
- Department of Astrophysics, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States)
- Center for Astrophysical Sciences, The Johns Hopkins University, Baltimore, MD 21218 (United States)
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
- INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117 Heidelberg (Germany)
- Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States)
Combining H{alpha} and IRAC images of the nearby spiral galaxy NGC 628, we find that between 30% and 43% of its 8 {mu}m dust emission is not related to recent star formation. Contributions from dust heated by young stars are separated by identifying H II regions in the H{alpha} map and using these areas as a mask to determine the 8 {mu}m dust emission that must be due to heating by older stars. Corrections are made for sub-detection-threshold H II regions, photons escaping from H II regions, and for young stars not directly associated with H II regions (i.e., 10-100 Myr old stars). A simple model confirms that this amount of 8 {mu}m emission can be expected given dust and PAH absorption cross sections, a realistic star formation history, and the observed optical extinction values. A Fourier power spectrum analysis indicates that the 8 {mu}m dust emission is more diffuse than the H{alpha} emission (and similar to observed H I), supporting our analysis that much of the 8 {mu}m-emitting dust is heated by older stars. The 8 {mu}m dust-to-H{alpha} emission ratio declines with galactocentric radius both within and outside of H II regions, probably due to a radial increase in disk transparency. In the course of this work, we have also found that intrinsic diffuse H{alpha} fractions may be lower than previously thought in galaxies, if the differential extinction between H II regions and diffuse regions is taken into account.
- OSTI ID:
- 22167290
- Journal Information:
- Astrophysical Journal, Vol. 762, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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