May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40032f&link_type=abstract
Spitzer Proposal ID #40032
Other
Scientific paper
Spitzer/IRS observations are the ideal tool to investigate puzzling ISO results on the spectra of PAHs in M31. The SINGS Legacy project has convincingly demonstrated that the 6-8um PAH bands dominate the mid-IR spectrum of star-forming galaxies, carrying a significant fraction of the total infrared luminosity. But ISOCAM spectro-imaging observations of M31 showed that the nucleus and bulge of this galaxy had very odd PAH spectra, bright at 11.3um and 12.7 microns but lacking the usual 6.2, 7.7 and 8.6 micron bands. The IRAC images clearly show that there is non-stellar emission in the 8 micron band in both the bulge and nucleus, as well as in the star-forming ring where the ISO spectra were more 'normal'. It has been suggested that the unusual ISO spectra are due to neutral (as opposed to the usual ionized) PAHs in regions with weak UV fields, possibly due to the presence of an AGN. We propose to map 11 regions in M31 with IRS spectral maps covering the wavelength range 5-20 microns (SL+LL2). The regions to be mapped include the nucleus, two regions observed by ISOCAM, and 9 other regions chosen for a range of dust temperatures, UV intensities and metallicities. We will measure the variation in relative strength of the PAH bands and its dependence on environment. M31 offers a unique laboratory for mapping PAH variations within a well-studied galaxy, furthering our understanding of these astrophysically important bands.
Ashby Matthew
Barmby Pauline
Devereux Nick
Fazio Giovanni
Gordon Karl
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