(Proposal ID) S14B-004

(PI) Tanaka Masayuki

(Proposal Title)
 Direct measurement  of the formation timescale of massive cluster ellipticals

(Abstract)
We were awarded two nights with MOSFIRE in S14A, but we collected no science 
data due to bad weather.  We request to carry out the observation again. We 
propose to obtain high-S/N spectra of massive quiescent galaxies at z~2 with 
MOSFIRE to tackle the long-standing issue of the formation of massive cluster 
ellipticals.  We have performed MOIRCS observations of two high-z groups 
(z=1.61 and 2.16) and identified 4-5 massive quiescent galaxies in each 
system. Our MOIRCS spectra are not of sufficient quality for detailed 
absorption studies and we propose to observe these quiescent galaxies with 
sensitive MOSFIRE. Our goal is to observationally constrain the formation 
timescale of massive cluster ellipticals by measuring spectral indices that 
are sensitive to different star formation timescales. We also measure stellar 
velocity dispersion, which gives us the dynamical mass and constrains the 
fundamental plane of the cluster galaxies at this high redshift for the first 
time. Our observations will place the strongest direct constraints to date on 
the physical processes that drive massive cluster galaxy formation and provide 
powerful inputs to numerical simulations to understand the detailed physics. 
This is a short proposal but will make a significant leap forward in this area.