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 ≤ 15) at z ≤ 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 σ level, and its amplitude is measured to be r0 = 8.6 ± 2.0 h-1 Mpc (in a Λ cold dark matter [ΛCDM] 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, MDMH ~ 1012.7 h-1 M⊙ (1012.0–1013.5 h-1 M⊙ at 1 σ confidence level). Finally, we use the clustering data to infer the physical properties of local AGNs, obtaining MBH ~ 2 × 108 h-1 M⊙ (1 × 107–3 × 109 h-1 M⊙) for the mass of the active black holes, τAGN ~ 8 × 106 yr (2 × 106–5 × 107 yr) for their lifetime and η ~ 0.14 for their efficiency (always for a ΛCDM model).