AAS 197, January 2001
Session 3. QSO Absorbers and the IGM
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

## [3.03] A Cluster of MgII Absorbers in a Large Quasar Group at 1.20 < z < 1.38

G.M. Williger (NASA/GSFC), L.E. Campusano (U. de Chile), R.G. Clowes (U. Central Lancashire, UK)

We have conducted a survey for MgII absorber systems toward the largest structure in the sky at z>0.2, a large quasar group consisting of at least 15 quasars at 1.20\circ \times 2.5\circ on the sky (~200 \times 100 h-2 Mpc2) and depth 156 (210) h-1 comoving Mpc for \Omega0=1 (\Omega0=0.2), H0\equiv 100h km s-1 Mpc-1, \Lambda=0. It is one of a handful of large quasar groups (Graham, Clowes, & Campusano 1995), which are believed to indicate a physical enhancement in the underlying density of the universe when the universe was about 1/3 of its present age. We can test for this mass excess by searching for spatially correlated metal absorption line systems, seen in the spectra of quasars situated in the background of the group. We have obtained spectra of 23 quasars with z>1.2 distributed over a ~2\times 2\circ area embedded in the quasar group, to survey for MgII at 0.70