SIMBAD references

We have studied the photometric properties of four fields around the high-redshift quasar pairs QP 1310+0007, QP 1355-0032, QP 0110-0219, and QP 0114-3140 at z∼1 with the aim of identifying large-scale structures (galaxy clusters or groups) around them. This sample was observed with the Gemini Multi-Object Spectograph (GMOS) at the Gemini North and South telescopes in the g', r', i', and z' bands, and our photometry is complete to a limiting magnitude of i'∼24 mag (corresponding to ∼M^*_i'+2 at the redshift of the pairs). Our analysis reveals that QP 0110-0219 shows very strong and QP 1310+0007 and QP 1355-0032 show some evidence for the presence of rich galaxy clusters in direct vicinity of the pairs. On the other hand, QP 0114-3140 could be an isolated pair in a poor environment. This work suggest that z∼1 quasar pairs are excellent tracers of high-density environments, and the same technique may be useful to find clusters at higher redshifts.