(Proposal ID) S10A-006

(PI) Tanaka, Masayuki

(Proposal Title)
Deep NIR spectroscopy of record-breaking cluster candidates at z~1.8

(Abstract)
We were awarded time in S07B and S09A (4 nights in total), but the observations
 were not successful due to bad weather. Here we request to carry out the 
observation again. We propose to observe 2 record-breaking high redshift 
(z ~ 1.8) cluster candidates with MOIRCS as a pilot survey of more intensive 
follow-ups in the near future. The cluster candidates show an extended X-ray 
emission and a clear red sequence of galaxies at high significance levels 
(> 4 sigma). This suggest that they are very likely real clusters. This is all 
we can do with the existing photometric data and what we need now is 
spectroscopic confirmations and detailed analyses of stellar populations of 
galaxies with the spectra. Optical spectroscopy of such high-z red objects is 
a real challenge and MOIRCS is the only instrument sensitive enough to do it 
with a reasonable amount of time. We show that our observation is feasible in 
the Scientific Justification. We aim (1) to confirm the record-breaking X-ray 
clusters spectroscopically and (2) to examine stellar populations of galaxies 
in the high-z clusters and address the formation mechanism of massive cluster 
ellipticals.