Two close large quasar groups of size ~ 350 Mpc at z ~ 1.2

Abstract

The Clowes & Campusano large quasar group (LQG) at ¯z = 1.28 has been re-examined using the quasar data from the DR7QSO catalogue of the Sloan Digital Sky Survey. In the 1991 discovery, the LQG impinged on the northern, southern and eastern limits of the survey. In the DR7QSO data, the western, northern and southern boundaries of the LQG remain essentially the same, but an extension eastwards of ∼2◦ is indicated. In the DR7QSO data, the LQG has 34 members, with ¯z = 1.28. A new group of 38 members is indicated at ¯z = 1.11 and within ∼2.◦0 of the Clowes & Campusano LQG. The characteristic sizes of these two LQGs, ∼350–400 Mpc, appear to be only marginally consistent with the scale of homogeneity in the concordance cosmology. In addition to their intrinsic interest, these two LQGs provide locations in which to investigate early large-scale structure in galaxies and to identify high-z clusters. A method is presented for assessing the statistical significance and overdensity of groups found by linkage of points.