AGN environments in the sloan digital sky survey I. Dependence on type, redshift, and luminosity

Natalie E. Strand, Robert J. Brunner, Adam D. Myers

Research output: Contribution to journalArticlepeer-review


We explore how the local environment is related to the redshift, type, and luminosity of active galactic nuclei (AGNs). 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 a higher density of galaxies on small scales where mergers are more likely to take place. However, in this picture, the activity observed in low-luminosity AGNs 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 on kiloparsec scales around spectroscopic type I and type II quasars to the local density around lower luminosity spectroscopic type I and type II AGNs. To minimize projection effects and evolution in the photometric galaxy sample we use to characterize AGN environments, we place our random control sample at the same redshift as our AGNs and impose a narrow redshift window around both the AGNs and control targets. We find that higher luminosity AGNs have more overdense environments compared to lower luminosity AGNs on all scales out to our 2 h70-1 Mpc limit. In addition, in the range 0.3 ≤ z ≤ 0.6, type II quasars have similarly overdense environments to those of bright type I quasars on all scales out to our 2 h70-1 Mpc limit, while the environment of dimmer type I quasars appears to be less overdense than the environment of type II quasars. We see increased overdensity for type II AGNs compared to type I AGNs on scales out to our limit of 2 h70-1 Mpc in overlapping redshift ranges. We also detect marginal evidence for evolution in the number of galaxies within 2 h70-1 Mpc of a quasar with redshift.

Original languageEnglish (US)
Pages (from-to)180-189
Number of pages10
JournalAstrophysical Journal
Issue number1
StatePublished - Nov 20 2008


  • Cosmology: observations
  • Large-scale structure of universe
  • Quasars: general
  • Surveys

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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