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