A Herschel Study of 24 micron-Selected AGNs and Their Host Galaxies

TL;DR

This study analyzes 290 mid-infrared-selected AGNs at redshifts 0.3 to 2.5, using spectral templates to decompose their energy distributions and estimate key properties like star formation rates and black hole masses.

Contribution

It introduces a comprehensive spectral decomposition method for AGNs and their hosts using Herschel data, revealing high luminosity AGNs are common in the surveyed fields.

Findings

Most AGNs have luminosities > 10^{45} ergs/s

Detected AGNs host supermassive black holes of ~3 x 10^8 Msun

Infrared-selected AGNs are more numerous than SDSS counterparts

Abstract

We present a sample of 290 24-micron-selected active galactic nuclei (AGNs) mostly at z ~ 0.3 -- 2.5, within 5.2 square degrees distributed as 25' X 25' fields around each of 30 galaxy clusters in the Local Cluster Substructure Survey (LoCuSS). The sample is nearly complete to 1 mJy at 24 microns, and has a rich multi-wavelength set of ancillary data; 162 are detected by Herschel. We use spectral templates for AGNs, stellar populations, and infrared 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 (SFRs), 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 ones typically have luminosities > 10^{45} ergs/s, and supermassive black holes of ~ 3 X 10^8 Msun emitting at ~ 10% of the Eddington rate. We find them in about twice the numbers of AGN identified in SDSS data in the same fields, i.e., they represent typical high luminosity AGN, not an infrared-selected minority. These AGNs and their host galaxies are studied further in an accompanying paper.