The environment of low redshift quasar pairs

TL;DR

This study examines the environments of 14 low-redshift quasar pairs, finding they reside in typical galaxy densities similar to isolated quasars, suggesting their activation is not environment-dependent.

Contribution

It provides the first detailed analysis of the galaxy environments of low-redshift quasar pairs, showing they are not in overdense regions unlike some expectations.

Findings

Quasar pairs are in regions of modest galaxy overdensity.

Their environments are similar to those of isolated quasars.

Activation of close quasar pairs does not require special environments.

Abstract

We investigate the properties of the galaxy environment of a sample of 14 low redshift (z $<$ 0.85) quasar physical pairs extracted from SDSS DR10 archives. The pairs have a systemic radial velocity difference $\Delta V_\parallel \leqslant$ 600 $km \ s^{-1}$ (based on [OIII]5007 \AA \ line) and projected distance $ R_\bot \leqslant$ 600 kpc. The physical association of the pairs is statistically confirmed at a level of $\sim$ 90 %. For most of the images of these quasars we are able to resolve their host galaxies that turn out to be on average similar to those of quasars not in pairs. We also found that quasars in a pair are on average in region of modest galaxy overdensity extending up 0.5 Mpc from the QSO. This galaxy overdensity is indistinguishable from that of a homogeneous sample of isolated quasars at the same redshift and with similar host galaxy luminosity. These results, albeit derived from a small (but homogeneous) sample of objects, suggest that the rare activation of two quasars with small physical separation does not require any extraordinary environment.