Seminars at FGG

Probing the accretion history of local AGN with clustering in the SWIFT-BAT survey

Speaker: Nico Cappelluti (INAF - Osservatorio Astronomico di Bologna)

Date and time: 2011-03-25 11:00

We present the clustering measurement of hard X-ray selected AGN in the local Universe. We used a sample of 199 sources spectroscopically confirmed detected by Swift-BAT in its 15-55 keV all-sky survey. We measured the real space projected auto-correlation function and detected a signal significant on projected scales lower than 200 Mpc/h. We measured a correlation length of r0= 5.56 (+0.49 -0.43) Mpc/h and a slope gamma=1.64 (+0.08 -0.07). We also measured the auto-correlation function of Type I and Type II AGN and we found an higher correlation length for Type I AGN. We produce a 1-2 sigma evidence of luminosity dependent clustering of AGN, as we detected a larger correlation length of luminous AGN than that of low luminosity sources. We have estimated the bias factor of Swift-BAT AGN that, according to the luminosity of the objects, is in the range 0.8-2.3, corresponding to a typical AGN host dark halo mass Log(M_DMH) ~ 12-14 M/M_sun, depending on the subsample. For the whole sample we measured Log(M_DMH) ~ 13.15 M/M_sun, which is the typical mass of a galaxy group. We estimated that the local AGN population has a typical lifetime of ~ 0.7 Gyr, it is powered by SMBH with mass MBH ~ 1-10 10^8 Msun accreting with very low efficiency, Log(epsilon) ~ 2.0. We also conclude that local AGN host galaxies are typically red-massive galaxies with mass of the order 2-8 10^10 Msun. We compared our results with clustering predictions of merger-driven AGN triggering models and found a good agreement. We also propose a plausible scenario for the accretion history of local AGN.