Quasar pairs with arcminute angular separations

¹ Institut d'Astrophysique, Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium
² Astronomical Observatory of Kyiv University, Observatorna St. 3, UA- 04053 Kyiv, Ukraine

Corresponding author: J. Surdej, surdej@astro.ulg.ac.be

Received: 19 October 2000
Accepted: 16 February 2001

Abstract

We use the Véron-Cetty & Véron ([CITE]) catalog (VV) of 13 213 quasars to investigate their possible physical grouping over angular scales . We first estimate the number of quasar pairs that would be expected in VV assuming a random distribution for the quasar positions and taking into account observational selection effects affecting heterogeneous catalogs. We find in VV a statistically significant (>3σ) excess of pairs of quasars with similar redshifts () and angular separations in the range, corresponding to projected linear separations or . There is also some excess in the range corresponding to Mpc in projected linear separations. If most of these quasar pairs do indeed belong to large physical entities, these separations must represent the inner scales of huge mass concentrations (cf. galaxy clusters or superclusters) at high redshifts; but it is not excluded that some of the pairs may actually consist of multiple quasar images produced by gravitational lensing. Of course, a fraction of these pairs could also arise due to random projections of quasars on the sky. The list of 11 pairs of quasars with redshift differences and angular separations is presented in order to stimulate further observational studies and to better understand the astrophysical and cosmological significance of these interesting objects.