  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.
