The environment of low-redshift quasar pairs

Abstract

We investigate the properties of the galaxy environment of a sample of 14 low-redshift (z < 0.85) quasar (QSO) physical pairs extracted from Sloan Digital Sky Survey Data Release 10 archives. The pairs have a systemic radial velocity difference ΔV|| ≤ 600 km s-1 (based on [O III]5007 Å line) and projected distance R⊥ ≤ 600 kpc. The physical association of the pairs is statistically confirmed at a level of ~90 per cent. For most of the images of these QSOs we are able to resolve their host galaxies that turn out to be on average similar to those of QSOs not in pairs. We also found that QSOs 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 QSOs 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 QSOs with small physical separation does not require any extraordinary environment.