The Environment of Active Galactic Nuclei in the Sloan Digital Sky Survey

Abstract

We present the observed fraction of galaxies with an active galactic nucleus (AGN) as a function of environment in the early data release of the Sloan Digital Sky Survey (SDSS). Using 4921 galaxies in the redshift range 0:05 z 0:095 and brighter than M r à ð Þ ¼ À20:0 (or M à þ 1:45), we find at least $20% of these galaxies possess an unambiguous detection of an AGN, but this fraction could be as high as '40% after we model the ambiguous emission-line galaxies in our sample. We have studied the environmental dependence of galaxies, using the local galaxy density as determined from the distance to the 10th nearest neighbor. As expected, we observe that the fraction of star-forming galaxies decreases with density, while the fraction of passive galaxies (no emission lines) increases with density. In contrast, the fraction of galaxies with an AGN remains constant from the cores of galaxy clusters to the rarefied field population. We conclude that the presence of an AGN is independent of the disk component of a galaxy. We have extensively tested our results, and they are robust against measurement error, definition of an AGN, aperture bias, stellar absorption, survey geometry, and signal-to-noise ratio. Our observations are consistent with the hypothesis that a supermassive black hole resides in the bulge of all massive galaxies, and '40% of these black holes are seen as AGNs in our sample. A high fraction of local galaxies with an AGN suggests either that the mean lifetime of these AGNs is longer than previously thought (i.e., !10 8 yr) or that the AGNs burst more often than expected: $40 times over the redshift range of our sample.

The complete census of optically selected AGNs in the Coma supercluster: the dependence of AGN activity on the local environment

“…dominated by Seyferts) with increasing galaxy environment density, mainly because the most powerful AGNs are hosted by late-type galaxies, which are the least likely to exist in dense environments. Popesso & Biviano (2006) found that the AGN fraction decreases with the increasing velocity dispersion of galaxies in groups and clusters, being higher in dense, low-dispersion groups, in contrast to the findings of Shen et al (2007) & Miller et al (2003) who found that the frequency of low activity AGNs does not correlate with environment.…”

Local Supermassive Black Holes, Relics of Active Galactic Nuclei and the X-ray background

“…More recently, Miller et al (2003) found from SDSS data that a very high fraction of galaxies host an AGN (∼ 20 − 40%) suggesting lifetimes longer than previously thought (i.e. > 10 8 yr).…”

Active Galactic Nuclei in the Sloan Digital Sky Survey. I. Sample Selection

“…There have been several studies identifying AGNs spectroscopically from different subsamples of SDSS galaxies ( Kauffmann et al 2003a;Miller et al 2003). Both studies have focused on narrow-line AGNs identified from the diagnostic diagrams.…”

“…Both studies have focused on narrow-line AGNs identified from the diagnostic diagrams. Miller et al (2003) found AGN signatures in at least 20% of 4921 galaxies in the redshift range 0:05 < z < 0:095 and studied the environment of these AGNs. Kauffmann et al (2003a) selected 22,623 narrow-line AGNs from a parent sample of 122,808 galaxies and studied their host galaxy properties.…”