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

Almudena Alonso-Herrero, Pablo G. Pérez-González, George H. Rieke, David M. Alexander, Jane R. Rigby, Casey Papovich, Jennifer L. Donley, Dimitra Rigopoulou

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


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 < 1044 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.

Original languageEnglish (US)
Pages (from-to)127-136
Number of pages10
JournalAstrophysical Journal
Issue number1
StatePublished - Apr 10 2008


  • Galaxies: active
  • Galaxies: evolution
  • Galaxies: high-redshift
  • Galaxies: stellar content
  • Infrared: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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