The environment of active galactic nuclei in the Sloan Digital Sky Survey

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 less than or equal to z less than or equal to 0.095 and brighter than M(r*) = -20.0 (or M* + 1.45), we find at least similar to 20% of these galaxies possess an unambiguous detection of an AGN, but this fraction could be as high as similar or equal to40% 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 similar or equal to 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., greater than or equal to 10(8) yr) or that the AGNs burst more often than expected: similar to 40 times over the redshift range of our sample.