Overdensity of galaxies in the environment of quasar pairs

TL;DR

This study finds that low-redshift quasar pairs are generally surrounded by denser galaxy environments compared to isolated quasars, suggesting a link between galaxy environment and nuclear activity, with some exceptions.

Contribution

It provides the first comparative analysis of galaxy overdensities around quasar pairs versus isolated quasars at low redshift.

Findings

Quasar pairs are typically in denser galaxy environments than isolated quasars.

Closest quasar pairs tend to inhabit poorer environments.

Results imply a complex relationship between quasar activity and environment.

Abstract

We report on a study of the galaxy environments of low redshift physical quasars pairs. We selected 20 pairs having projected separation $<$ 0.5 Mpc and difference of systemic velocity $<$ 800 km s$^{-1}$. Using Sloan Digital Sky Survey images we evaluated the galaxy overdensity around these quasars in pairs and then compare it with that of a sample of isolated quasars with same redshift and luminosity. It is found that on average there is a systematic larger overdensity of galaxies around quasars in pairs with respect to that of isolated quasars. This may represent a significant link between nuclear activity and galaxy environment. However, at odds with that, the closest quasar pairs seem to inhabit poorer environments. Implications of present results and perspectives for future work are briefly discussed.