No overdensity of Lyman Alpha Emitting Galaxies around a quasar at z~5.7
  Bright quasars, observed when the Universe was less than one billion years
old (z>5.5), are known to host massive black holes (~10$^{9}$ M$_{\odot}$), and
are thought to reside in the center of massive dark matter overdensities. In
this picture, overdensities of galaxies are expected around high redshift
quasars. However, observations based on the detection of Lyman Break Galaxies
(LBGs) around these quasars do not offer a clear picture: this may be due to
the uncertain redshift constraints of LBGs, which are selected through
broad-band filters only. To circumvent such uncertainties, we here perform a
search for Lyman Alpha Emitting galaxies (LAEs) in the field of the quasar PSO
J215.1512-16.0417 at z~5.73, through narrow band, deep imaging with FORS2 at
the VLT. We study an area of 37 arcmin$^{2}$, i.e. ~206 comoving Mpc$^{2}$ at
the redshift of the quasar. We find no evidence for an overdensity of LAEs in
the quasar field with respect to blank field studies. Possible explanations for
these findings include that our survey volume is too small, or that the strong
ionizing radiation from the quasar hinders galaxy formation in its immediate
proximity. Another possibility is that these quasars are not situated in the
dense environments predicted by some simulations.
