your ID: 0156 
First Name: Cheng 
Last Name: Li 
Affiliation: Center for Astrophysics, USTC 
Title: The clustering of narrow-line AGN in the local Universe 
Authors: Cheng Li, Guinevere Kauffmann, Lan Wang, Simon White, Timothy M. Heckman, Y.P.Jing 
Topic: 1 
Session: oral 
Abstract: 
We have analyzed the clustering of $\\sim 90,000$  narrow-line AGN drawn from the Data Release 4 (DR4) 
of the  Sloan Digital Sky Survey. Our analysis aims to address the following  questions:
a) How do the locations of galaxies within the large-scale distribution of dark matter influence  ongoing 
    accretion onto their central black holes? 
b) Is AGN activity triggered by interactions or mergers between galaxies? 
To answer these questions, we compute the cross-correlation between AGN and a 
reference sample of galaxies drawn from the DR4.  We compare this  to the results obtained for   
control samples of non-AGN  that are matched simultaneously in redshift, stellar mass, 
concentration, velocity dispersion  and in  mean stellar age, as measured by the 4000 \\AA\\ break 
strength. We also compare near-neighbour counts around AGN and the control galaxies. On  scales 
larger than a few Mpc, AGN have the same clustering amplitude as the control sample. This  demonstrates 
that AGN host galaxies and non-AGN control galaxies populate dark matter halos of similar masses. On 
scales between 100 kpc and 1 Mpc, AGN are clustered more weakly than the control galaxies. We use mock 
catalogues constructed from high-resolution N-body simulations to interpret this anti-bias  and we show 
that the observed effect can be easily understood if AGN are preferentially located at the centres of 
their dark matter halos. On scales less than 30-40 kpc, AGN are clustered  more strongly than the 
control sample, but the effect is  weak. When compared to the control sample, we find that only 
one in a hundred  AGN have have an extra neighbour within a radius of 30 kpc. This excess 
does not increase appreciably as a function of the accretion rate onto the black hole. Although 
interactions may be responsible for triggering nuclear activity in a few AGN, some other mechanism 
is required to explain the activity seen in the majority of the objects in our sample.