Galaxies spatially coincident with the JKCS041 X-ray emission display a
  red sequence at z~2.2
  New deep z'-J data readly show a narrow red sequence co-centered with, and
similary concentrated to, the extended X-ray emission of the cluster of
galaxies JKCS041. The JKCS041 red sequence is 0.32+/-0.06 mag redder in z'-J
than the red sequence of the zspec=1.62 IRC0218A cluster, putting JKCS041 at
z<<1.62. The colour difference of the two red sequences gives a red-sequence
based redshift of z=2.20+/-0.11 for JKCS041, where the uncertainty accounts for
uncertainties in stellar synthesis population models, in photometric
calibration and in the red sequence colour of both JKCS041 and IRC0218A
clusters.
