The host galaxies and black holes of typical z ∼ 0.5-1.4 AGNs

Abstract

10 pags., 9 figs. ; We study the stellar and star formation properties of the host galaxies of 58 X-ray-selected AGNs in the GOODS portion of the Chandra Deep Field South (CDF-S) region at z ∼ 0.5-1.4. The AGNs are selected such that their rest-frame UV to near-infrared spectral energy distributions (SEDs) are dominated by stellar emission; i.e., they show a prominent 1.6 μm bump, thus minimizing the AGN emission >contamination.> This AGN population comprises approximately 50% of the X-ray-selected AGNs at these redshifts. We find that AGNs reside in the most massive galaxies at the redshifts probed here. Their characteristic stellar masses (M*, ∼ 7.8 × 10 10 and M* ∼ 1.2 × 1011 M⊙ at median redshifts of 0.67 and 1.07, respectively) appear to be representative of the X-ray-selected AGN population at these redshifts and are intermediate between those of local type 2 AGNs and high-redshift (z ∼ 2) AGNs. The inferred black hole masses (MBH ∼ 2 × 108 M ⊙) of typical AGNs are similar to those of optically identified quasars at similar redshifts. Since the AGNs in our sample are much less luminous (L2-10 kev downsizing> is due to both a decrease in the characteristic stellar mass of typical host galaxies and less efficient accretion. Finally, there is no strong evidence in AGN host galaxies for either highly suppressed star formation (expected if AGNs played a role in quenching star formation) or elevated star formation when compared to mass-selected (i.e., IRAC-selected) galaxies of similar stellar masses and redshifts. © 2008. The American Astronomical Society. All rights reserved. ; This work was supported by NASA through contract 1255094 issued by the JPL/California Institute of Technology. A. A.-H. acknowledges support from the Spanish Plan Nacional del Espacio under grant ESP2005-01480. P. G. P.-G. acknowledges support from the Ramon y Cajal Fellowship Program financed by the Spanish Government, and from the Spanish Programa Nacional de Astronomıa y Astrofısica under grant AYA 2006-02358. This research has made use of the NASA/ IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration ; Peer Reviewed