The clustering of low-luminosity active galactic nuclei

Based on the Sloan Digital Sky Survey (SDSS) DR2 sample, we present a multiparameter analysis of the spatial clustering of nearby active galactic nuclei (AGNs). Estimates of the redshift-space two-point correlation function reveal that Seyferts are less clustered than normal galaxies, while LINERs' clustering amplitude (s(0)) is consistent with that of the parent galaxy population. This difference in clustering is not driven by the morphology-density relation, as colors and concentration indices follow similar distributions. The fact that objects of given spectral types are clustered differently seems correlated with a variety of their physical properties, including L-[OI], L-[OIII], the emitting gas density n(e), and the obscuration level. LINERs, which exhibit high s0, show the lowest luminosities and obscuration levels, and relatively low ne, suggesting that these objects harbor relatively massive black holes that are weakly active or inefficient in their accretion, probably due to the insufficiency of their fuel supply. Seyfert galaxies, which have low s0, are very luminous and show large ne, suggesting that their black holes are less massive but accrete quickly and efficiently enough to clearly dominate the ionization. Star-forming galaxies, the H (IIS), are weakly clustered; this trend can be understood as a consequence of both the morphology-density and star formation rate-density relations. The spectral properties of the H (II) galaxies suggest, however, that they hide in their centers, amid large amounts of obscuring material, black holes of generally low mass whose activity remains relatively feeble. Our own Milky Way may be such a case.