The Angular Clustering of WISE-Selected AGN: Different Haloes for Obscured and Unobscured AGN

DONOSO, E.; YAN, LIN; STERN, D.; ASSEF, R. J.

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Londres; Año: 2014 vol. 789 p. 44 - 57

0004-637X

We calculate the angular correlation function for a sample of $sim$170,000 AGN extracted from the {it Wide-field Infrared Survey Explorer} (wise) catalog, selected to have red mid-IR colors ($W1 - W2 > 0.8$) and $W2 < 15.05$ (e.g., 4.6~$mu$m flux densities brighter than 0.14~mJy). The sample is expected to be $> 90%$ reliable at identifying AGN, and to have a mean redshift of $langle z angle=1.1$. In total, the angular clustering of wise AGN is roughly similar to that of optical AGN, though we find that the AGN with the reddest mid-IR colors display a slightly higher clustering strength than the full AGN sample. We cross-match these objects with the photometric SDSS catalog and distinguish obscured sources with $r - W2 > 6$ from bluer, unobscured AGN. Obscured sources present a higher clustering signal than unobscured sources. Since the host galaxy morphologies of wise-selected obscured AGN are not typical red sequence elliptical galaxies and, in fact, show disks in many cases, it is unlikely that the increased clustering strength of the obscured population is driven by a host galaxy segregation bias. By using relatively complete redshift distributions from the COSMOS survey, we find obscured sources at $langle z angle sim 0.9$ have a bias of $b = 2.9 pm 0.6$ and are hosted in dark matter halos with a typical mass of $log(M/M_odot, h^{-1})sim 13.5$. In contrast, unobscured AGN at $langle z angle sim 1.1$ have a bias of $b = 1.6 pm 0.6$ and inhabit halos of $log(M/M_odot, h^{-1}) sim 12.4$. These findings suggest that obscured AGN inhabit denser environments than unobscured AGN, and are difficult to reconcile with the simplest AGN unification models, such as obscuring torus models, where obscuration is driven solely by orientation.