AEGIS: The Clustering of X-Ray Active Galactic Nucleus Relative to Galaxies at z ~ 1
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2009
- DOI:
- 10.1088/0004-637X/701/2/1484
- arXiv:
- arXiv:0902.0363
- Bibcode:
- 2009ApJ...701.1484C
- Keywords:
-
- galaxies: active;
- galaxies: high-redshift;
- large-scale structure of universe;
- X-rays: galaxies;
- Astrophysics - Cosmology and Extragalactic Astrophysics
- E-Print:
- 18 pages, accepted to ApJ, minor changes made to match accepted version, Figure 1 added