ACTIVE GALACTIC NUCLEI CLUSTERING IN THE LOCAL UNIVERSE: AN UNBIASED PICTURE FROM SWIFT -BAT

Abstract

We present the clustering measurement of hard X-ray selected active galactic nuclei (AGNs) 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 autocorrelation function (ACF) and detected a signal significant on projected scales lower than 200 Mpc h −1 . We measured a correlation length of r 0 = 5.56−0.43 Mpc h −1 and a slope γ = 1.64−0.08 −0.07 . We also measured the ACF of Type I and Type II AGNs and found higher correlation length for Type I AGNs. We have a marginal evidence of luminosity dependent clustering of AGNs, as we detected a larger correlation length of luminous AGNs than that of low-luminosity sources. The corresponding typical host dark matter halo masses of Swift-BAT are ∼ log(M DMH )∼ 12-14 h −1 M/M , depending on the subsample. For the whole sample, we measured log(M DMH )∼ 13.15 h −1 M/M which is the typical mass of a galaxy group. We estimated that the local AGN population has a typical lifetime τ AGN ∼0.7 Gyr, it is powered by supermassive black hole with mass M BH ∼ (1-10) × 10 8 M and accreting with very low efficiency, log( )∼ −2.0. We also conclude that local AGN host galaxies are typically red-massive galaxies with stellar mass of the order (2-80) × 10 10 h −1 M . We compared our results with clustering predictions of merger-driven AGN triggering models and found a good agreement.

THE SPATIAL CLUSTERING OFROSATALL-SKY SURVEY ACTIVE GALACTIC NUCLEI. IV. MORE MASSIVE BLACK HOLES RESIDE IN MORE MASSIVE DARK MATTER HALOS

“…Cappelluti et al (2010) and Koutoulidis et al (2013) verify this finding using different AGN samples at different redshifts. Koutoulidis et al (2013) use a large sample of ∼1500 AGNs from the Chandra Deep Field (CDF) North and South, the extended CDF South, COSMOS, and AEGIS.…”

THE 60 MONTH ALL-SKY BURST ALERT TELESCOPE SURVEY OF ACTIVE GALACTIC NUCLEUS AND THE ANISOTROPY OF NEARBY AGNs

“…The reason why BAT does not detect this anisotropy in the local scale structure is ultimately due to statistics. Indeed, the typical clustering length of the BAT AGN is known to be 5-8 Mpc (Cappelluti et al 2010). Within 85 Mpc, our 20 • search cone subtends 9 a length of ∼16 Mpc which is comparable to the clustering length of AGNs.…”

“…Indeed, the median redshift of the radio-quiet AGNs detected by BAT is ∼0.03 which corresponds to ∼120 Mpc. On these scales, the structure of the local universe is known to be inhomogeneous and AGNs are known to trace the matter density distribution (Cappelluti et al 2010). The BAT AGNs can thus be used to trace the large-local scale structure.…”

Imprints of the super-Eddington accretion on the quasar clustering

“…Future observations of high-redshift quasar clustering will allow us to make more accurate comparisons to the model we introduced here and to estimate the role of super-Eddington accretion process during BH growth. For X-ray selected AGNs, Cappelluti et al (2010) have shown the weak X-ray luminosity dependence of AGN clustering. Future theoretical studies are needed to explain the luminosity dependent clustering of these relatively low luminosity AGNs.…”