Physical pairs of quasars with large separation on the sky

Abstract

Quasars and quasar-like objects from the Palomar bright quasar survey show an apparent aggregation and pairing. Nearest neighbor statistical tests here show physical pairing at confidence levels up to 99.8%. At their redshift distance, however, the separation of the pairs is in the range (30–150) h −1 Mpc. Such separations are an order of magnitude larger than the dimensions of superclusters. Using the mean redshifts of the pairs as a measure of their distance yields a three-dimensional average distribution in space. For those quasars with separations ≲50 h −1 Mpc this distribution is not spherical, but elongated toward the observer. If this elongation is caused by peculiar velocities it would have to arise from the expansion of the quasars away from each other. Such deviations from the Hubble flow would have to be ≳2000 km s −1. In an independent analysis performed on two other samples of quasars, Fang (private communication) derived peculiar velocities of 600 to 1800 km s −1 for weakly clustered pairs at separations of ≲ 100 h −1 Mpc.