Occupation of X-ray-selected galaxy groups by X-ray active galactic nuclei

V. Allevato, A. Finoguenov, G. Hasinger, T. Miyaji, N. Cappelluti, M. Salvato, G. Zamorani, R. Gilli, M. R. George, M. Tanaka, M. Brusa, J. Silverman, F. Civano, M. Elvis, F. Shankar

Research output: Contribution to journalArticlepeer-review

58 Scopus citations


We present the first direct measurement of the mean halo occupation distribution (HOD) of X-ray-selected active galactic nuclei (AGNs) in the COSMOS field at z ≤ 1, based on the association of 41 XMM and 17 C-COSMOS AGNs with member galaxies of 189 X-ray-detected galaxy groups from XMM-Newton and Chandra data. We model the mean AGN occupation in the halo mass range log M 200 [M] = 13-14.5 with a rolling-off power law with the best-fit index α = 0.06(- 0.22; 0.36) and normalization parameter fa = 0.05(0.04; 0.06). We find the mean HOD of AGNs among central galaxies to be modeled by a softened step function at logMh >logMmin = 12.75(12.10, 12.95)M while for the satellite AGN HOD we find a preference for an increasing AGN fraction with Mh , suggesting that the average number of AGNs in satellite galaxies grows slower (αs < 0.6) than the linear proportion (αs = 1) observed for the satellite HOD of samples of galaxies. We present an estimate of the projected autocorrelation function (ACF) of galaxy groups over the range of rp = 0.1-40 h -1Mpc at 〈z〉 = 0.5. We use the large-scale clustering signal to verify the agreement between the group bias estimated by using the observed galaxy groups ACF and the value derived from the group mass estimates. We perform a measurement of the projected AGN-galaxy-group cross-correlation function, excluding from the analysis AGNs that are within galaxy groups and we model the two-halo term of the clustering signal with the mean AGN HOD based on our results.

Original languageEnglish (US)
Article number47
JournalAstrophysical Journal
Issue number1
StatePublished - Oct 10 2012
Externally publishedYes


  • X-rays: general
  • dark matter
  • galaxies: active
  • large-scale structure of universe
  • quasars: general
  • surveys

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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