The bolometric output and host-galaxy properties of obscured AGN in the XMM-COSMOS survey^⋆

¹ Dipartimento di AstronomiaUniversità di Bologna, via Ranzani 1, 40127 Bologna, Italy
e-mail: elisabeta.lusso2@unibo.it
² INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
³ Institute for Astronomy, 2680 Woodlawn Drive, University of Hawaii, Honolulu, HI 96822, USA
⁴ Max Planck Institut für extraterrestische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
⁵ Excellence Cluster Universe, TUM, Boltzmannstr. 2, 85748 Garching bei München, Germany
⁶ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁷ ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁸ ETH Zürich, Physics Department, 8093 Zürich, Switzerland
⁹ Universidad de Concepción, Departamento de Astronomìa, Casilla 160-C, Concepción, Chile
¹⁰ University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064, USA
¹¹ Space Telescope Science Institute, Baltimore, Maryland 21218, USA

Received: 2 May 2011
Accepted: 24 August 2011

Abstract

We present a study of the multi-wavelength properties, from the mid-infrared to the hard X-rays, of a sample of 255 spectroscopically identified X-ray selected type-2 AGN from the XMM-COSMOS survey. Most of them are obscured and the X-ray absorbing column density is determined by either X-ray spectral analyses (for 45% of the sample), or from hardness ratios. Spectral energy distributions (SEDs) are computed for all sources in the sample. The average SEDs in the optical band are dominated by the host-galaxy light, especially at low X-ray luminosities and redshifts. There is also a trend between X-ray and mid-infrared luminosity: the AGN contribution in the infrared is higher at higher X-ray luminosities. We calculate bolometric luminosities, bolometric corrections, stellar masses and star formation rates (SFRs) for these sources using a multi-component modeling to properly disentangle the emission associated to stellar light from that due to black hole accretion. For 90% of the sample we also have the morphological classifications obtained with an upgraded version of the Zurich estimator of structural types (ZEST+). We find that on average type-2 AGN have lower bolometric corrections than type-1 AGN. Moreover, we confirm that the morphologies of AGN host-galaxies indicate that there is a preference for these type-2 AGN to be hosted in bulge-dominated galaxies with stellar masses greater than 10¹⁰ solar masses.