The clustering of narrow-line AGN in the local Universe

Abstract

We have analyzed the clustering of ~ 90,000 narrow-line AGN drawn from the Data Release 4 (DR4) of the SDSS. We compute the cross-correlation between AGN and a reference sample of galaxies, and compare this to results for control samples of inactive galaxies matched simultaneously in redshift,stellar mass,concentration, velocity dispersion and the 4000A break strength. We also compare near-neighbour counts around AGN and around the control galaxies. On scales larger than a few Mpc, AGN have almost the same clustering amplitude as the control sample. This demonstrates that AGN host galaxies and inactive galaxies populate dark matter halos of similar mass.On scales between 100kpc and 1Mpc,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, showing that the observed effect is easily understood if AGN are preferentially located at the centres of their dark matter halos. On scales less than 70 kpc, AGN cluster marginally 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 has an extra neighbour within a radius of 70 kpc. This excess increases as a function of the accretion rate onto the black hole, but it does not rise above the few percent level. Although interactions between galaxies may be responsible for triggering nuclear activity in a minority of nearby AGN, some other mechanism is required to explain the activity seen in the majority of the objects in our sample. (abridged)Comment: 14 pages, 11 figures, accepted to MNRAS, Fig.2 redrawn and text slightly change

Triggering active galactic nuclei in hierarchical galaxy formation: disk instability vs. interactions

“…In fact, they are not expected to yield an appreciable enhancement in the clustering of AGN hosts (see Taniguchi 1999; see also Stewart 2009;Lotz et al 2011). Thus the controversial observational results concerning the clustering of the AGN hostssee Li et al (2006), Pierce et al (2007), Darg et al (2010) for negative evidence, and Alonso et al (2007), Woods & Geller (2007), Rogers et al (2009), Koss (2010, and Ellison (2011) for an enhanced fraction of close pairs of AGN hosts compared to control samples -can hardly provide a definite clue to the minor merging/fly-by scenario (also because of the dependence of the results on the clustering scale). A support for the interactionbased picture can be found in the bluer colours of galaxies close to AGN hosts (see Shirasaki et al 2011;Kollatschny et al 2012), and in the observations of specific individual cases (see, e.g., Gonzalez Delgado et al 2002;Anderson et al 2013 and references therein).…”

The AMIGA sample of isolated galaxies

“…Major interactions have been proposed as a mechanism to trigger AGN activity in some cases (see review by Combes 2003;Ellison et al 2011;Liu et al 2012), although no clear relation was found in some studies using the SDSS (Li et al 2006(Li et al , 2008. Seyferts do not require external interactions to be fueled (e.g.…”

Large-scale variations of the cosmic X-ray background and the X-ray emissivity of the local Universe

“…Basilakos & Plionis 2006). Supporting evidence that AGNs closely trace the distribution of galaxies was recently presented by Li et al (2006) based on an optically selected sample of narrow-line AGNs from the Sloan Digital Sky Survey.…”