(Proposal ID) S13A-059

(PI) Koyama, Yusei

(Proposal Title)
Resolving the nature of strong starbursts within z>2 proto-cluster galaxies

(Abstract)
Our recent narrow-band H alpha survey of three distant proto-clusters at 
z=2.16 (PKS1138), z=2.46 (4C23.56), and z=2.53 (USS1558) revealed that a 
significant fraction of proto-cluster galaxies are undergoing strong 
starbursts. We find that z>2 proto-cluster galaxies tend to have redder 
colours and higher stellar mass (with M_* >10^11M_sun) compared to general 
field galaxies. Such massive starbursts produced within the proto-cluster 
environments must be the promising progenitors of the quiescent, spheroidal 
galaxies in local clusters. We here propose high-resolution imaging 
observation of these galaxies with IRCS+AO188 (with LGS-AO mode). By spatially 
resolving stellar mass (with rest-frame optical imaging) as well as J-K colour 
distribution within the galaxies on ~1 kpc scale, we aim to (1) study rest-
frame optical morphology of ~60 proto-cluster galaxies and test if the proto-
cluster galaxies already obtained large, spheroidal morphology at z>2; 
(2) quantify the role of major/minor mergers based on the mass fraction 
between the merging clumps within the galaxies; (3) map colour gradient 
within the galaxies and identify where the most intense star formation is 
taking place, in order to identify the physical driver of the boosted 
activity in the high-z proto-cluster environments.