The Small-Scale Environment of Quasars

Abstract

Where do quasars reside? Are quasars located in environments similar to those of typical L* galaxies, and, if not, how do they differ? An answer to this question will help shed light on the triggering process of quasar activity. We use the Sloan Digital Sky Survey to study the environment of quasars and compare it directly with the environment of galaxies. We find that quasars (M_i < -22, z < 0.4) are located in higher local overdensity regions than are typical L* galaxies. The enhanced environment around quasars is a local phenomenon; the overdensity relative to that around L* galaxies is strongest within 100 kpc of the quasars. In this region, the overdensity is a factor of 1.4 larger than around L* galaxies. The overdensity declines monotonically with scale to nearly unity at ~1 Mpc, where quasars inhabit environments comparable to those of L* galaxies. The small-scale density enhancement depends on quasar luminosity, but only at the brightest end: the most luminous quasars reside in higher local overdensity regions than do fainter quasars. The mean overdensity around the brightest quasars (M_i < -23.3) is nearly three times larger than around L* galaxies while the density around dimmer quasars (M_i = -22.0 to -23.3) is ~1.4 times that of L* galaxies. By ~0.5 Mpc, the dependence on quasar luminosity is no longer significant. The overdensity on all scales is independent of redshift to z = 0.4. The results suggest a picture in which quasars typically reside in L* galaxies, but have a local excess of neighbors within ~0.1 - 0.5 Mpc; this local density excess likely contributes to the triggering of quasar activity through mergers and other interactions.

Accepted by ApJ; 7 pages, 5 figures

References in corpus (1)

• The 2.5 m Telescope of the Sloan Digital Sky Survey

Cited by in corpus (20)

• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: I. Galaxy Mergers & Quasar Activity
• Clustering of High Redshift ($z\ge 2.9$) Quasars from the Sloan Digital Sky Survey
• Minor Galaxy Interactions: Star Formation Rates and Galaxy Properties
• Clustering Analyses of 300,000 Photometrically Classified Quasars--I. Luminosity and Redshift Evolution in Quasar Bias
• Quasars Probing Quasars II: The Anisotropic Clustering of Optically Thick Absorbers around Quasars
• The clustering of narrow-line AGN in the local Universe
• Interactions, star formation and AGN activity
• Supermassive Black Holes in the Hierarchical Universe: A General Framework and Observational Tests
• Quasars: What turns them off?
• The SDSS-DR5 Survey for Proximate Damped Lya Systems
• The transverse proximity effect in the z ~ 2 Lyman-alpha forest suggests QSO episodic lifetimes of ~1 Myr
• Average Properties of a Large Sample of z_abs ~ z_em associated Mg II Absorption Line Systems
• AGN Environments in the Sloan Digital Sky Survey I: Dependence on Type, Redshift, and Luminosity
• A 3-Dimensional study of the Local Environment of Bright IRAS Galaxies: The AGN/Starburst connection
• X-ray selected AGN in groups at redshifts z~1
• On the Connection Between Metal Absorbers and Quasar Nebulae
• Deep optical spectroscopy of extended Lyman alpha emission around three radio-quiet z=4.5 quasars
• Astrophysics in 2006
• Clustering environment of BL Lac object RGB 1745+398
• The distant red galaxy neighbour population of 1 < z < 2 QSOs and optically obscured sources