The Angular Clustering of WISE-selected AGN: Different Halos for Obscured and Unobscured AGN

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

Córdoba

Conferencia; 57a Reunión Asociación Argentina de Astronomía; 2014

Asociación Argentina de Astronomía

We calculate the angular correlation function for a sample of ∼170,000 extracted from the Wide-File Infrared Survey Explorer (WISE) catalog, selected to have red mid-IR colors (W1-W2>0.8) and 4.6 μm 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 z = 1. In total, the angular clustering of WISE AGN is roughly similar to that of optical AGN. 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 angular clustering signal than unobscured sources. Since the host galaxy morphology of obscured AGN are not typical red sequence elliptical galaxies and show disks in many cases, it is not likely 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 z = 0.9 have a bias of b=2.9±0.6 and are hosted in dark matter halos with typical mass of log(M/M_sun h^-1)∼13.5. In contrast, unobscured AGN at z = 1.1 have a bias of b=1.6±0.6 and inhabit halos of log(M/M_sun h^-1)∼12.4. These findings suggest that unobscured AGN inhabit denser environments than unobscured AGN, and are difficult to reconcile with the simplest AGN unification models where obscuration is driven solely by orientation of an obscuring dusty torus.