A Herschel study of 24 μm-selected AGNs and their host galaxies

Abstract

We present a sample of 290 24 μm-selected active galactic nuclei (AGNs) mostly at z ∼ 0.3-2.5, within 5.2 deg 2 distributed as 25′ x 25′ fields around each of 30 galaxy clusters in the Local Cluster Substructure Survey. The sample is nearly complete to 1 mJy at 24 μm, and has a rich multiwavelength set of ancillary data; 162 are detected by Herschel. We use spectral templates for AGNs, stellar populations, and infrared (IR) emission by star-forming galaxies to decompose the spectral energy distributions (SEDs) of these AGNs and their host galaxies, and estimate their star formation rates, AGN luminosities, and host galaxy stellar masses. The set of templates is relatively simple: a standard Type-1 quasar template; another for the photospheric output of the stellar population; and a far-infrared star-forming template. For the Type-2 AGN SEDs, we substitute templates including internal obscuration, and some Type-1 objects require a warm component (T ≳ 50 K). The individually Herschel-detected Type-1 AGNs and a subset of 17 Type-2 AGNs typically have luminosities >10 45 ergs s -1, and supermassive black holes of ∼3 × 10 8 M ⊙ emitting at ∼10% of the Eddington rate. We find them in about twice the numbers of AGNs identified in SDSS data in the same fields, i.e., they represent typical high-luminosity AGNs, not an IRselected minority. These AGNs and their host galaxies are studied further in an accompanying paper.