Type 1 and type 2 quasars in the mid-infrared

Abstract

Type 2 or "obscured" AGN have long been identified at low AGN luminosities (e.g. Seyfert 2s) or through their radio luminosities (e.g. radio galaxies). But radio-quiet quasars (RQQs) are many times more common than radio-loud quasars, and it's therefore unsurprising that recent searches have revealed that radio-quiet quasar 2s also form significant population. Finding the numbers, properties, and redshift distribution of quasar 2s will be very important to resolving questions about the formation and co-evolution of black holes and galaxies. We have selected a sample of Type 2 and Type 1 quasars matched in their mid-infrared luminosity from the Spitzer First Look Survey by selecting on their mid-infrared dust emission properties (as measured by Spitzer IRAC photometry). This emission provides a distinctive signature of AGN activity but should not be affected by orientation or torus opening angle. We have obtained mid-infrared IRS spectroscopy of these samples to study star formation activity in the host galaxies and the dust environments of the AGN, using measurements of the PAH features, the shape of the mid-infrared SED, and the equivalent width of the silicate features at 10 microns. We find that the quasar 2s have more diverse mid-IR spectral properties, and that obscuration of the AGN is linked to star formation activity in the host.

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