Spitzer IRS observations of k+a galaxies: A link between PAH emission properties and AGN feedback?

Abstract

We have performed IRS low resolution 5-12 micron spectroscopy on a sample of galaxies selected to be at 3 distinct post-starburst evolutionary stages based on their optical spectral indices. The resulting IRS spectra show distinctive PAH emission line structures at 6.2, 7.7, 8.6 and 11.3 micron and little silicate absorption, indicative of ongoing star formation. However the PAH inter-line ratios, in particular the 11.3/6.2 micron and 7.7/6.2 micron ratio, show large variations. These variations are found to correlate with both time since the most recent starburst and AGN activity. We speculate that the evolution observed in these PAH ratios is related to an increase in AGN activity with time since star burst.

13 pages, 3 figures, accepted for publication in ApjL

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• Evolution Through the Post-Starburst Phase: Using Post-Starburst Galaxies as Laboratories for Understanding the Processes that Drive Galaxy Evolution
• After The Fall: The Dust and Gas in E+A Post-Starburst Galaxies
• Welcome to the Twilight Zone: The Mid-Infrared Properties of Poststarburst Galaxies
• Starburst and post-starburst high-redshift protogalaxies: The feedback impact of high energy cosmic rays