Compatibility of the Large Quasar Groups with the Concordance Cosmological Model

TL;DR

This study assesses whether large quasar groups, including the exceptionally large Huge-LQG, are compatible with the standard cosmological model by comparing observations with simulations and analyzing their statistical significance.

Contribution

It demonstrates that the largest quasar groups are consistent with the concordance cosmological model through mock catalog comparisons and extreme value analysis.

Findings

Huge-LQG's size is consistent with expectations from the model.

The probability of observing a group as large as Huge-LQG is 0.3%.

Such large structures are expected in larger cosmic volumes.

Abstract

We study the compatibility of large quasar groups with the concordance cosmological model. Large Quasar Groups are very large spatial associations of quasars in the cosmic web, with sizes of 50-250h^-1 Mpc. In particular, the largest large quasar group known, named Huge-LQG, has a longest axis of ~860h^-1 Mpc, larger than the scale of homogeneity (~260 Mpc), which has been noted as a possible violation of the cosmological principle. Using mock catalogues constructed from the Horizon Run 2 cosmological simulation, we found that large quasar groups size, quasar member number and mean overdensity distributions in the mocks agree with observations. The Huge-LQG is found to be a rare group with a probability of 0.3 per cent of finding a group as large or larger than the observed, but an extreme value analysis shows that it is an expected maximum in the sample volume with a probability of 19 per cent of observing a largest quasar group as large or larger than Huge-LQG. The Huge-LQG is expected to be the largest structure in a volume at least 5.3 +- 1 times larger than the one currently studied.