Two close Large Quasar Groups of size ~ 350 Mpc at z ~ 1.2

TL;DR

This paper re-examines a large quasar group at z ~ 1.2 using SDSS data, discovering a second nearby group of similar size, challenging cosmological homogeneity assumptions and offering new insights into early large-scale structure.

Contribution

The study identifies a second large quasar group near the known one, using a new method to assess statistical significance and overdensity of such structures.

Findings

Two large quasar groups of size ~350 Mpc identified at z ~ 1.2 and 1.11.

The two groups are only marginally consistent with the scale of homogeneity.

A new method for assessing statistical significance of quasar groups is presented.

Abstract

The Clowes & Campusano (1991) 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 \sim 2 deg 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 \sim 2.0 deg of the Clowes & Campusano LQG. The characteristic sizes of these two LQGs, \sim 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.