ACP Seminar (Astronomy - Cosmology - Particle Physics)

Speaker: Takamitsu Miyaji (UNAM)
Title: Clustering of AGNs from the ROSAT All-Sky Survey and Halo Occupation Distribution
Date (JST): Tue, Dec 07, 2010, 12:15 - 13:15
Place: Seminar Room A
Abstract: In this seminar, I present the results of our recent studies on clustering of low redshift broad-line AGNs (BLAGN) selected from the catalog of ROSAT all-sky survey AGNs. We utilize the two-point cross-correlation function (CCF) of ROSAT BLAGNs and luminous red galaxies (LRGs) in the SDSS to overcome the limitation on the small-number statistics in the AGN clustering measurements. We have applied the Halo Occupation Distribution (HOD) modeling to the AGN-LRG CCF to in accurately model the correlation function, to determining the linear bias parameter, and to derive not only the mean DMH mass that AGNs resides, but also to determine how AGNs distribute among the DMHs.

We found that the mean DMH mass in which the AGN reside is log <M_h>~13.1 (M_h in h^{-1}) solar masses, which approximately corresponds the mass of galaxy groups, and the clustering amplitude depends on X-ray luminosity. As a result of HOD analysis, we prefer models where the average number of AGN per DMH halo grows slower than the DMH mass itself, unlike the general galaxy population. This means that the AGN fraction among galaxies decrease with the DMH mass. Possible explanations of this trend are the ram-pressure stripping/evaporation of galaxy cold gas by intragroup/intracluster hot gas and the inefficiency of merging in galaxy encounters in the higher velocity dispersion environment.