A Herschel SPIRE Study of M81: Separating Cold and Warm PAH Emissions

Details A Herschel SPIRE Study of M81: Separating Cold and Warm PAH Emissions A Herschel SPIRE Study of M81: Separating Cold and Warm PAH Emissions

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21833004l&link_type=abstract

American Astronomical Society, AAS Meeting #218, #330.04; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

We study correlations among three distinct dust emission components in the interstellar medium of the galaxy M81 at a sub-kpc resolution: (a) I_8, the surface brightness of non-stellar emission in Spitzer IRAC 8 um band, dominated by the so-called PAH emission features, (b) I_24, that of hot continuum emission in Spitzer MIPS 24 um band, arising from small dust grains powered mainly by young stars, and (c) I_500, that of cold dust continuum emission in Herschel SPIRE 500 um band, from large dust grains heated by evolved stars. Both I_8/I_500 and I_24/I_500 ratios increase towards active star-forming regions, consistent with the view that both (a) and (b) are correlated with current star formation. But as I_24/I_500 decreases to zero, I_8/I_500 approaches to a finite, positive value of 0.05 or greater. This implies that 57% of the 8 um non-stellar emission is "cold," arising from regions, where the 24 um emission is relatively insignificant. Since it is likely that the fraction of this cold component in the PAH emission varies from galaxy to galaxy, making the PAH luminosity a rather poor star formation tracer in general.

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