The structure and evolution of a forming galaxy cluster at z = 1.62
  We present a comprehensive picture of the Cl0218.3-0510 protocluster at
$z=1.623$ across 10 co-moving Mpc. Using filters that tightly bracket the
Balmer and 4000 Angstrom breaks of the protocluster galaxies we obtain precise
photometric redshifts resulting in a protocluster galaxy sample that is 89+/-5%
complete and has a contamination of only 12+/-5%. Both star forming and
quiescent protocluster galaxies are located allowing us to map the structure of
the forming cluster for the first time. The protocluster contains 6 galaxy
groups, the largest of which is the nascent cluster. Only a small minority of
the protocluster galaxies are in the nascent cluster (11%) or in the other
galaxy groups (22%), as most protocluster galaxies reside between the groups.
Unobscured star forming galaxies predominantly reside between the
protocluster's groups, whereas red galaxies make up a large fraction of the
groups' galactic content, so observing the protocluster through only one of
these types of galaxies results in a biased view of the protocluster's
structure. The structure of the protocluster reveals how much mass is available
for the future growth of the cluster and we use the Millennium Simulation,
scaled to a Planck cosmology, to predict that Cl0218.3-0510 will evolve into a
2.7x 10^14 Msun cluster by the present day.
