The existence of large scale structure at high redshift () provides an important constraint on theories for the formation of structure and evolution of the Universe. One approach to probing for such structure is through the study of intervening metal line absorption systems in quasar spectra. Such systems are believed to trace galaxies through their extended gaseous halos.
Statistical analysis of the redshift distribution of available samples of quasar absorption systems suggest that large scale clustering on comoving scales up to 100 Mpc may have been in place already at z2-3 (e.g. Quashnock et al. 1996).
The complementary technique of probing for large scale structure in the plane of the sky by searching for correlated absorption in adjacent lines of sight is hampered by the relatively low density of high redshift quasars bright enough for detailed absorption line work. Nonetheless, several potential high redshift `absorption superclusters' spanning tens of Mpc on the sky have been identified in this manner. These include the absorption systems seen toward PKS 0273-233 (Foltz et al. 1993); the two pairs of damped Ly systems seen at and toward Q2138-4427 and Q2139-4434 (Francis & Hewitt 1993; Francis et al. 1996); the apparent structures at and detected in a dense quasar field near the south Galactic pole by Williger et al. (1996); and the well-studied case of the strong absorption spanning in the field of the quasar pair Tol 1037-2703/1038-2712 (Jakobsen et al. 1986; Dinshaw & Impey 1996; Lespine & Petitjean 1997; and references therein).
With the aim of searching for further such cases of intervening high-redshift superclusters Romani et al. (1991) searched the quasar catalogs for suitable background objects near quasars known to display rich metal line absorption systems. One of the most promising fields identified by Romani et al. is that of the quasar Q0122-380, an object whose absorption spectrum contains at least seven C IV systems between (Carswell et al. 1982) and happens to lie within a field in which Savage et al. (1984) have carried out a deep objective prism quasar search. Q0122-380 is therefore surrounded by 11 quasar candidates of brightness 19-20 within a radius, corresponding to comoving distances Mpc at .
In this paper we present exploratory slit spectra and redshifts of these quasar candidates. As it turns out, several of the objects of interest are either not confirmed as quasars, or lie at significantly lower redshift than indicated by their preliminary catalog entries, thereby rendering the field toward Q0122-380 rather less promising for the purpose of searching for high redshift superclusters than originally thought.
© European Southern Observatory (ESO) 2000
Online publication: July 7, 2000