AGN Environments in the Sloan Digital Sky Survey I : Dependence on Luminosity

We explore how the local environment is related to the type and luminosity of AGN. Recent simulations and observations are converging on the view that the extreme luminosity of quasars is fueled in major mergers of gas-rich galaxies. In such a picture, quasars are expected to be located in regions with higher density of galaxies where mergers are more likely to take place. However, in this picture, the activity observed in low-luminosity AGN is due to secular processes that are less dependent on the local galaxy density. To test this hypothesis, we compare the local photometric galaxy density around Type I quasars on kiloparsec scales to the local density around low-luminosity, narrow line AGN and Type II quasars. We find that the mean overdensity of photometric galaxies around the environment of low-luminosity AGN is ≈ 1.7 times less than the mean overdensity around Type I quasars with significance > 3σ, but the environment density of photometric galaxies around Type II quasars is not significantly different than the environment around Type I quasars. We also find that on scales . 300 h 70 kpc, quasars with more massive black holes have an environment density 1.13 times (> 3σ) more than that of quasars with less massive black holes. It will be necessary for new merger models simulating the origin of quasars to explain why quasars with more massive black holes are formed in or ultimately end up in richer environments on scales . 300 h 70 kpc.