Aegis: The clustering of x-ray active galactic nucleus relative to galaxies at z 1

Alison L. Coil, Antonis Georgakakis, Jeffrey A. Newman, Michael C. Cooper, Darren Croton, Marc Davis, David C. Koo, Elise S. Laird, Kirpal Nandra, Benjamin J. Weiner, Christopher N.A. Willmer, Renbin Yan

Research output: Contribution to journalArticlepeer-review

134 Scopus citations


We measure the clustering of nonquasar X-ray active galactic nucleus (AGN) at z = 0.7-1.4 in the AEGIS field. Using the cross-correlation of 113 Chandra-selected AGN, with a median log L X = 42.8 erg s -1, with 5000 DEEP2 galaxies, we find that the X-ray AGNs are fitted by a power law with a clustering scale length of r 0 = 5.95 0.90 h -1 Mpc and slope γ = 1.66 0.22. X-ray AGNs have a similar clustering amplitude as red, quiescent and "green" transition galaxies at z 1 and are significantly more clustered than blue, star-forming galaxies. The X-ray AGN clustering strength is primarily determined by the host galaxy color; AGNs in red host galaxies are significantly more clustered than AGNs in blue host galaxies, with a relative bias that is similar to that of red to blue DEEP2 galaxies. We detect no dependence of clustering on optical brightness, X-ray luminosity, or hardness ratio within the ranges probed here. We find evidence for galaxies hosting X-ray AGN to be more clustered than a sample of galaxies with matching joint optical color and magnitude distributions. This implies that galaxies hosting X-ray AGN are more likely to reside in groups and more massive dark matter halos than galaxies of the same color and luminosity without an X-ray AGN. In comparison to optically selected quasars in the DEEP2 fields, we find that X-ray AGNs at z 1 are more clustered than optically selected quasars (with a 2.6σ significance) and therefore may reside in more massive dark matter halos. Our results are consistent with galaxies undergoing a quasar phase while in the blue cloud before settling on the red sequence with a lower-luminosity X-ray AGN, if they are similar objects at different evolutionary stages.

Original languageEnglish
Pages (from-to)1484-1499
Number of pages16
JournalAstrophysical Journal
Issue number2
StatePublished - 2009


  • Galaxies: active
  • Galaxies: high-redshift
  • Large-scale structure of universe
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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