Mid-infrared selection of dusty AGN

Abstract

We present results from the spectroscopic follow-up of a sample of candidate obscured AGN selected in the mid-infrared from the Spitzer First Look Survey. Our selection allows a direct comparison of the numbers of obscured and unobscured AGN at a given luminosity for the first time, and shows that the ratio of obscured to unobscured AGN in an 8μm-selected sample with infrared luminosities corresponding to low luminosity quasars is ≈ 1 : 1 at z ~0.5. Most of our optically-faint candidate obscured AGN have the high-ionization, narrowline spectra expected from type-2 AGN. We discuss techniques for selecting such samples at longer infrared wavelengths to reduce the selection bias against highly-obscured and high redshift objects inherent in our IRAC-based selection technique.

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