The SCUBA-2 Cosmology Legacy Survey: Ultraluminous star-forming galaxies
  in a z=1.6 cluster
  We analyse new SCUBA-2 submillimeter and archival SPIRE far-infrared imaging
of a z=1.62 cluster, Cl0218.3-0510, which lies in the UKIDSS/UDS field of the
SCUBA-2 Cosmology Legacy Survey. Combining these tracers of obscured star
formation activity with the extensive photometric and spectroscopic information
available for this field, we identify 31 far-infrared/submillimeter-detected
probable cluster members with bolometric luminosities >1e12 Lo and show that by
virtue of their dust content and activity, these represent some of the reddest
and brightest galaxies in this structure. We exploit Cycle-1 ALMA submillimeter
continuum imaging which covers one of these sources to confirm the
identification of a SCUBA-2-detected ultraluminous star-forming galaxy in this
structure. Integrating the total star-formation activity in the central region
of the structure, we estimate that it is an order of magnitude higher (in a
mass-normalised sense) than clusters at z~0.5-1. However, we also find that the
most active cluster members do not reside in the densest regions of the
structure, which instead host a population of passive and massive, red
galaxies. We suggest that while the passive and active populations have
comparable near-infrared luminosities at z=1.6, M(H)~-23, the subsequent
stronger fading of the more active galaxies means that they will evolve into
passive systems at the present-day which are less luminous than the descendants
of those galaxies which were already passive at z~1.6 (M(H)~-20.5 and
M(H)~-21.5 respectively at z~0). We conclude that the massive galaxy population
in the dense cores of present-day clusters were already in place at z=1.6 and
that in Cl0218.3-0510 we are seeing continuing infall of less extreme, but
still ultraluminous, star-forming galaxies onto a pre-existing structure.
