Other
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21924617s&link_type=abstract
American Astronomical Society, AAS Meeting #219, #246.17
Other
Scientific paper
We use mid-Infrared (MIR) spectroscopy from Spitzer to study star-formation and AGN processes in 65 IR-luminous galaxies at 0.02 < z < 0.6. The MIR spectra cover wavelengths 5-38µm, spanning the strongest polycyclic aromatic hydrocarbon (PAH) features and other important diagnostic lines. Our sample of galaxies spans the full range of rest-frame (u-r) optical color with F(24µm) > 1.2 mJy, which corresponds to total IR luminosity, L(IR)=1010-1012L&sun;, with a median L(IR) 1011L&sun;. We select a subset of galaxies with Spitzer IRAC 3.6-8.0µm colors indicative of warm dust heated by an AGN. Compared to IR-luminous galaxies with no indications of AGN, these IRAC-selected AGN show weaker PAH emission, which we attribute to an increase in MIR continuum from the AGN. We find that the luminosity in the PAH features correlates strongly with [Ne II] λ12.8µm emission in both the AGN and non-AGN subsamples. We find no measurable difference between the luminosity ratios of ionized and neutral PAHs, specifically the 7.7-to-11.3µm PAH ratio. This suggests that the AGN do not preferentially excite or destroy the PAH molecules on galaxy-wide scales, and in all IR-selected galaxies the PAH luminosity correlates strongly with the total SFR. A small subset of galaxies show a strong excess of [O IV] λ25.9µm emission for their PAH emission, indicating the presence of heavily-obscured AGN in galaxies. We compare the position of both the IR-AGN to other galaxies on an optical color-magnitude relation. The IRAC-selected AGN populate a range of color, primarily in the ``green valley'', implying their hosts are a mix of starburst and post-starburst galaxies. The [O IV]-excess objects in our sample lie toward the red end of the ``green valley''. Given their placement on the color-magnitude diagram, and their weak PAH emission, we conclude their IR luminosity is dominated by processes associated with the AGN.
Dey Arjun
Jannuzi Buell
Papovich Casey
Rieke George
Shipley Heath V.
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