(Proposal ID) S13B-084

(PI) Koyama, Yusei

(Proposal Title)
Unveiling the internal structure and stellar build-up within z=2 cluster 
galaxies

(Abstract)
We propose AO-assisted broad-band (K-band) and narrow-band (H_2[1-0]; lambda_c=
2.122mum) imaging observation with IRCS+AO188 (LGS mode) of an Halpha-selected 
proto-cluster field at z = 2.23. The cluster is discovered from our extensive 
~100-Mpc scale Halpha emitter survey (HiZELS) in the COSMOS field. Importantly,
 the H_2 filter on IRCS is perfectly matched with the NB_K filter (on UKIRT) 
that we used for selecting z = 2.23 Halpha emitters. Therefore the above filter
 combination will provide us with a very unique opportunity to spatially 
resolve their Halpha emissions (hence stellar build-up) within individual 
galaxies on ~1-kpc scale. Our goals are: (1) to directly measure the size and 
Halpha luminosity of individual star-forming clumps within the galaxies to 
test if the young cluster galaxies accompany giant Hii regions with boosted 
activity, or if their Hii regions are simply following the same scaling 
relation as for high-z field galaxies; (2) we also aim to measure the size of 
their stellar components (from K-band imaging). By comparing them with those 
of early-type galaxies in lower-z clusters (as well as with our field galaxy 
samples from HiZELS), we will determine when and how today's cluster early-
type galaxies obtained their large, bulge-dominated, spheroidal morphologies.