The Asiago-ESO/RASS QSO Survey. III. Clustering analysis and theoretical interpretation

This is the third paper in a series describing the Asiago-ESO/RASS QSO Survey (AERQS), a project aimed at the construction of an all-sky statistically well-defined sample of relatively bright quasi-stellar objects (QSOs; B less than or equal to 15) at z less than or equal to 0.3. We present here the clustering analysis of the full spectroscopically identified database (392 active galactic nuclei [AGNs]). The clustering signal at 0.02 < z < 0.22 is detected at a 3 - 4 sigma level, and its amplitude is measured to be r(0) = 8.6 +/- 2.0 h(-1) Mpc (in a Lambda cold dark matter [LambdaCDM] model). The comparison with other classes of objects shows that low-redshift QSOs are clustered in a way similar to radio galaxies, extremely red objects (EROs), and early-type galaxies in general, although with a marginally smaller amplitude. The comparison with recent results from the Two Degree Field (2dF) QSO Redshift Survey (2QZ) shows that the correlation function of QSOs is constant in redshift or marginally increasing toward low redshift. We discuss this behavior with physically motivated models, deriving interesting constraints on the typical mass of the dark matter halos hosting QSOs, M(DMH) similar to 10(12.7) h(-1) M(.) (10(12.0)-10(13.5) h(-1) M(.) at 1sigma confidence level). Finally, we use the clustering data to infer the physical properties of local AGNs, obtaining M(BH) similar to 2 x 10(8) h(-1) M(.) (1 x 10(7)-3 x 10(9) h(-1) M(.)) for the mass of the active black holes, tau(AGN) similar to 8 x 10(6) yr (2 x 10(6)-5 x 10(7) yr) for their lifetime and eta similar to 0.14 for their efficiency (always for a LambdaCDM model).