Discovery of an Overdensity of Lyman-alpha Emitters Around a $\mathrm{z}\sim4$ QSO with the Large Binocular Telescope

TL;DR

This study reports the discovery of a significant overdensity of Lyman-Break galaxies around a high-redshift quasar, suggesting that luminous QSOs at z~4 are located in massive, proto-cluster environments.

Contribution

First observational evidence of LBG overdensity around a z~4 QSO, linking QSOs to large-scale structure formation at high redshift.

Findings

Overdensity of LBGs near the QSO with a 0.02% chance of random occurrence

Four out of 15 LBGs with secure redshifts are consistent with QSO redshift

Supports the idea that luminous QSOs reside in large dark matter haloes

Abstract

Measurements of QSO clustering in the SDSS show that $\mathrm{z}>4$ QSOs are some of the most highly biased objects in the universe. Their large correlation lengths of $r_0 \sim 20h^{-1}$Mpc are comparable to the most massive clusters of galaxies in the universe today and suggest that these QSOs may mark the locations of massive cluster progenitors at high redshift. We report the discovery of an overdensity of LBGs around QSO SDSSJ114514.18+394715.9 as part of our survey to identify Lyman-Break galaxies (LBGs) around luminous $\mathrm{z}\sim4$ QSOs. In this field three of the eight LBGs with secure redshifts are consistent with the redshift of the QSO. We find that the likelihood that this is merely an apparent overdensity due to the chance selection of field galaxies is only 0.02%, based on comparisons to simulations and our modeled selection efficiency. Overall, our survey finds four of the 15 LBGs with secure redshifts are consistent with the redshifts of their respective QSOs, which is consistent with luminous QSOs residing in larger haloes.