Discovery of an overdensity of Lyman alpha emitters around a z ∼ 4 QSO with the Large Binocular Telescope

Measurements of QSO clustering in the SDSS show that z 4 QSOs are some of the most highly biased objects in the universe. Their large correlation lengths of r0 ∼ 20h−1Mpc are comparable to the most massive clusters of galaxies in the uni-verse 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 galax-ies (LBGs) around luminous z ∼ 4 QSOs. In this field three of the eight LBGs with secure redshifts are consistent with the redshift of the QSO. We find that the likeli-hood 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 con-sistent with the redshifts of their respective QSOs, which is consistent with luminous QSOs residing in larger haloes.