Abstract

The strong observed clustering of 3.5 quasars indicates that they are hosted by massive dark matter halos. Assuming that quasars and galaxies trace the same large-scale structures, this should manifest as strong clustering of galaxies around quasars. Previous works on high-redshift quasar environments have failed to find convincing evidence for these overdensities. Here we conduct a survey for Ly alpha emitters (LAEs) in the environs of 17 quasars at 4 probing scales of . We measure an average LAE overdensity of , which we quantify by fitting the quasar LAE cross-correlation function. We find consistency with a power-law shape with correlation length ;1.8 and rule out a zero clustering hypothesis at the 95% confidence level. We also measure the LAE autocorrelation length and find cMpc (;1.8), which is times higher than the value measured in blank fields. Taken together, our results clearly indicate that LAEs are significantly clustered around 4 quasars. We compare the observed clustering with the expectation from a deterministic bias model, whereby LAEs and quasars probe the same underlying dark matter overdensities, and find that our measurements fall short of the predicted overdensities by a factor of . We discuss possible explanations for this discrepancy, including large-scale quenching or the presence of excess dust in galaxies near quasars. Finally, the large cosmic variance from field to field observed in our sample (10/17 fields are actually underdense) cautions one from overinterpreting studies of 6 quasar environments based on a single or handful of quasar fields.