AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 87. QSO Absorption Line Systems
Display, Thursday, June 3, 1999, 9:20am-4:00pm, Southwest Exhibit Hall

## [87.03] MgII absorbers embedded in the 1040+05 quasar supercluster

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

The largest structure known at z>0.2 consists of a large group of at least 15 quasars at 1.21\circ \times 2.5\circ on the sky({\boldmath ~400 \times 200 h50-2} Mpc2). It is one of a handful of large quasar groups (Graham et al. 1995, MNRAS 275, 790), 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. One of the ways to test whether quasar groups are actually accompanied by a mass excess is to search for spatially correlated absorption line systems, seen in the spectra of quasars situated in the background of the group.

Using the CTIO-4m telescope, we have completed a spectroscopic survey of MgII absorption systems, by observing 23 quasars with z>1.2 distributed over a ~ 2\circ area embedded in the quasar group toward ESO/SERC field 927. Statistics for the redshift distribution of MgII absorbers with rest equivalent width W0(\lambda 2796) \geq 0.3 Å\ established by Steidel & Sargent et al. (1992, ApJS 80, 1 ) are used for comparison, and degree-wide structures are searched and compared with similar surveys at z>2 through CIV absorbers (Williger et al. 1996, ApJS 104, 145). Our current results are presented and discussed.

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