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 r 0 ∼ 20 h −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 Lyman-break galaxies (LBGs) around QSO SDSSJ 114514.18+394715.9 as part of our survey to identify 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 likelihood that this is merely an apparent overdensity due to the chance selection of field galaxies is only 0.02 per cent, based on comparisons to simulations and our modelled selection efficiency. Overall, our survey finds 4 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.