(Proposal ID) S11A-004

(PI) Tanaka, Masayuki

(Proposal Title)
Stellar Populations of Massive Galaxies in a z=2.15 Proto-cluster

(Abstract)
This is a resubmission of a proposal, which got accepted twice, but was almost 
entirely lost due to bad weather in S07B and S09A. We propose to observe a 
proto-cluster PKS1138 at z = 2.15 with MOIRCS. Based on a multi-band 
photometric analysis of galaxy properties in the cluster, we found that the 
cluster galaxies seem to be characterized by a shorter formation time scale 
compared to galaxies of similar mass and redshift in the field. To confirm 
this and obtain further insights into the physical process driving the rapid 
formation, we propose to obtain rest-frame optical spectra of the massive 
galaxies in PKS1138. We show that our observation is feasible based on 
simulations calibrated against realMOIRCS data. We will (1) double the number 
of spectroscopically confirmed z > 2 evolved galaxies and (2) fit stellar 
population synthesis models to the observed NIR spectra combined with the 
existing broadband U-8mum fluxes to derive physical properties such as stellar 
mass, age, and formation time scale. These properties will be compared with 
those of field galaxies of similar mass and redshift drawn from the literature 
to quantify the role of environment on galaxy formation. This is the first 
systematic spectroscopic survey of environmental effects at z > 2.