The Galaxy Environment of Quasars in the Clowes-Campusano Large Quasar Group at z~1.3

Abstract

The Clowes-Campusano Large Quasar Group (LQG) is the largest known structure at high redshifts, with at least 18 quasars at z~1.3 forming a structure ~200 Mpc across. We are conducting an ultra-deep optical and deep NIR study to examine the galaxy environment of quasars in this LQG to determine if, and how, LQGs trace large-scale structure at early epochs. We report significant associated clustering in the field of a z=1.226 quasar from this LQG in the form of a factor ~11 overdensity of I-K>3.75 galaxies, and red sequences of 15-18 galaxies at I-K~4.3,V-K~6.9, indicative of a population of massive ellipticals at the quasar redshift. The quasar is located between two groups of these galaxies, with further clustering extending over 2-3 Mpc. Within 30 arcsec of the quasar we find a concentration of blue (V-I<1) galaxies in a band that bisects the two groups of red sequence galaxies. This band is presumed to correspond to a region of enhanced star-formation. We suggest that the merging of the two groups of red sequence galaxies has triggered both the quasar and the band of star-formation. Quasars at z~1.3 are located in a variety of environments, but those with associated clustering are found on the cluster peripheries.