Growing up in a megalopolis: Environmental effects on galaxy evolution
  in a supercluster at z~0.65 in UKIDSS UDS
  We present a large-scale galaxy structure Cl J021734-0513 at z~0.65
discovered in the UKIDSS UDS field, made of ~20 galaxy groups and clusters,
spreading over 10 Mpc. We report on a VLT/VIMOS spectroscopic follow-up program
that, combined with past spectroscopy, allowed us to confirm four galaxy
clusters (M200 ~ 10^14 Msol) and a dozen associated groups and star-forming
galaxy overdensities. Two additional filamentary structures at z ~ 0.62 and z ~
0.69 and foreground and background clusters at 0.6 < z < 0.7 were also
confirmed along the line-of-sight. The structure subcomponents are at different
formation stages. The clusters have a core dominated by passive galaxies and an
established red sequence. The remaining structures are a mix of star-forming
galaxy overdensities and forming groups. The presence of quiescent galaxies in
the core of the latter shows that `preprocessing' has already happened before
the groups fall into their more massive neighbours. Our spectroscopy allows us
to derive spectral index measurements e.g. emission/absorption line equivalent
widths, strength of the 4000A break, valuable to investigate the star formation
history of structure members. Based on these line measurements, we select a
population of `poststarburst' galaxies. These galaxies are preferentially found
within the virial radius of clusters, supporting a scenario in which their
recent quenching could be prompted by gas stripping by the dense intracluster
medium. We derive stellar age estimates using MCMC-based spectral fitting for
quiescent galaxies and find a correlation between ages and colours/stellar
masses which favours a top-down formation scenario of the red sequence. A
catalogue of ~650 redshifts in UDS will be released alongside the paper.
