2016ApJ...828...43W

A population of quasars at z ∼ 2 is determined based on dust luminosities νL_ν(7.8 µm) that includes unobscured, partially obscured, and obscured quasars. Quasars are classified by the ratio νL_ν(0.25 µm)/νL_ν(7.8 µm)=UV/IR, assumed to measure obscuration of UV luminosity by the dust that produces IR luminosity. Quasar counts at rest-frame 7.8 µm are determined for quasars in the Bootes field of the NOAO Deep Wide Field Survey using 24 µm sources with optical redshifts from the AGN and Galaxy Evolution Survey (AGES) or infrared redshifts from the Spitzer Infrared Spectrograph. Spectral energy distributions are extended to far-infrared wavelengths using observations from the Herschel Space Observatory Spectral and Photometric Imaging Receiver (SPIRE), and new SPIRE photometry is presented for 77 high-redshift quasars from the Sloan Digital Sky Survey. It is found that unobscured and obscured quasars have similar space densities at rest-frame 7.8 µm, but the ratio L_ν(100 µm)/L_ν(7.8 µm) is about three times higher for obscured quasars than for unobscured, so that far-infrared or submillimeter quasar detections are dominated by obscured quasars. We find that only ∼5% of high-redshift submillimeter sources are quasars and that existing 850 µm surveys or 2 mm surveys should already have detected sources at z ∼ 10 if quasar and starburst luminosity functions remain the same from z=2 until z=10.