(Proposal ID) S15A-045

(PI) Koyama, Yusei

(Proposal Title)
 MOIRCS follow-up spectroscopy of an extremely rich galaxy cluster at z=1.52

(Abstract)
This is the resubmission of our approved programme (S14B-112), which was 
unfortunately cancelled due to the direct hit of a strong typhoon. This 
proposal aims to perform a follow-up spectroscopy of a strong over-density 
of galaxies around a radio galaxy at z=1.52 (4C65.22), newly discovered by 
our recent broad-band and narrow-band (Halpha) imaging with Subaru. We find 
that the highest-density region (cluster core) is clearly dominated by red-
sequence galaxies, while the Halpha-emitting star-forming (SF) galaxies are 
preferentially located in the outskirt region. This spatial segregation of 
passive/SF population resembles like lower-redshift clusters, suggesting the 
newly discovered structure is a well-developed system. Our science goals are: 
(1) to map 3-D dynamics of member galaxies and measure the cluster total mass 
to examine the evolution of cluster mass-normalised SFR (Sigma SFR/M_{cl}), 
(2) to study the environmental effects on the mass--metallicity relation at 
z=1.5 by using [NII]/Halpha ratio, (3) to test environmental impacts on the 
excitation properties of inter-stellar medium (ISM) within the galaxies via 
[OIII]/Halpha ratio, and (4) to test if the red galaxies dominating cluster 
core are really completely quiescent, or if they exhibit any signature of 
residual SF or nuclear activity.