VIMOS Ultra-Deep Survey (VUDS): Witnessing the Assembly of a Massive
  Cluster at z~3.3
  Using new spectroscopic observations obtained as part of the VIMOS Ultra-Deep
Survey (VUDS), we perform a systematic search for overdense environments in the
early universe ($z>2$) and report here on the discovery of Cl J0227-0421, a
massive protocluster at $z=3.29$. This protocluster is characterized by both
the large overdensity of spectroscopically confirmed members,
$\delta_{gal}=10.5\pm2.8$, and a significant overdensity in photometric
redshift members. The halo mass of this protocluster is estimated, by a variety
of methods, to be roughly $3\times10^{14}$ $\mathcal{M}_{\odot}$ at $z\sim3.3$,
which, evolved to $z=0$ results in a halo mass rivaling or exceeding that of
the Coma cluster. The properties of 19 spectroscopically confirmed member
galaxies are compared with a large sample of VUDS/VVDS galaxies in lower
density field environments at similar redshifts. We find tentative evidence for
an excess of redder, brighter, and more massive galaxies within the confines of
the protocluster relative to the field population, which suggests that we may
be observing the beginning of environmentally-induced quenching. The properties
of these galaxies are investigated, including a discussion of the brightest
protocluster galaxy which appears to be undergoing vigorous coeval nuclear and
starburst activity. The remaining member galaxies appear to have
characteristics which are largely similar to the field population. Though we
find weaker evidence of the suppression of the median star formation rates
amongst and differences in stacked spectra of member galaxies with respect to
the field, we defer any conclusions of these trends to future work with the
ensemble of protostructures that are found in the full VUDS sample.
