Revisiting the clustering of narrow-line AGN in the local Universe: Joint dependence on stellar mass and colour

Abstract

We investigate the clustering and dark halo properties for the narrow-line active galactic nuclei (AGN) in the Sloan Digital Sky Survey (SDSS), particularly examining the joint dependence on galaxy mass and colour. AGN in galaxies with blue colours or massive red galaxies with M∗ ≳ 1010.5M⊙ are found to show almost identical clustering amplitudes at all scales to control galaxies of the same mass, colour, and structural parameters. This suggests AGN activity in blue galaxies or massive red galaxies is regulated by internal processes, with no correlation with environment. The antibias of AGN at scales between ∼100 kpc and a few Mpc, as found in Li et al. (2006b) for the AGN as a whole, is observed only for the AGN hosted by galaxies with the red colours and relatively low masses (< 1010.5M⊙). A simple halo model in which AGN are preferentially found at dark halo centres can reproduce the observational results but requires a mass-dependent central fraction, which is a factor of ∼4 higher than the fraction estimated from the SDSS group catalogue. The same group catalogue reveals that the host groups of AGN in red satellites tend to have lower halo masses than the control galaxies, while the host groups of the AGN in red centrals tend to form earlier, as indicated by a larger stellar mass gap between the two most massive galaxies in the groups. Our result implies that the mass assembly history of dark haloes may play an additional role in the AGN activity in low-mass red galaxies.