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

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 similar to 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 mu m 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* similar to 7.8 x 10(10) and M* similar to 1.2 x 10(11) M-circle dot 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 similar to 2) AGNs. The inferred black hole masses ( M-BH similar to 2 x 10(8) M-circle dot) 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) < 10(44) erg s(-1)) than quasars, typical AGNs have low Eddington ratios (eta similar to 0.01-0.001). This suggests that, at least at intermediate redshifts, the cosmic AGN 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.