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 ~ 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 × 10^11 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 (M_BH ~ 2 × 10^8 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 (L_2–10 keV < 10^44 erg s^−1) than quasars, typical AGNs have low Eddington ratios (η ~ 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.

The evolutionary paths among galaxy types on the red sequence at 0.3 < Z < 1.5

We have studied the main evolutionary paths among the galaxy types residing on the massive end of the Red Sequence and nearby locations on the Green Valley during the last ∼9 Gyr. The morphological and star formation properties of a sample of these galaxies at 0 . 3 < z < 1 .5 with stellar masses M_∗ > 5 × 10^10 M_⊙ have been analysed. We present direct observational evidence for the first time of the existence of two main evolutionary paths among the different red galaxy types since z ∼ 1 .5, which provide some clues on the nature of the processes that have governed the assembly of present-day massive quiescent galaxies. The results are in excellent agreement with the hierarchical evolutionary framework proposed in the Eliche-Moral et al. (2010) model. Data from SHARDS (one of the ESO/GTC Large Programmes approved in 2009A) will complement and improve the present findings, shedding some light into many of the still unsettled questions concerning the migration of galaxies from the Blue Cloud to the Red Sequence at z < 1 .5.