Early Quenching of Massive Protocluster Galaxies Around z=2.2 Radio
  Galaxies
  Radio galaxies are among the most massive galaxies in the high redshift
universe and are known to often lie in protocluster environments. We have
studied the fields of seven z = 2.2 radio galaxies with HAWK-I narrow-band and
broad-band imaging in order to map out their environment using Halpha emitters
(HAEs). The results are compared to the blank field HAE survey HiZELS. All of
the radio galaxy fields are overdense in HAEs relative to a typical HiZELS
field of the same area and four of the seven are richer than all except one of
65 essentially random HiZELS subfields of the same size. The star formation
rates of the massive HAEs are lower than those necessary to have formed their
stellar population in the preceding Gyr - indicating that these galaxies are
likely to have formed the bulk of their stars at higher redshifts, and are
starting to quench.
