(Proposal ID) S14A-051

(PI) Tanaka Masayuki

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

(Abstract)
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 by measuring their precise formation timescale as well as 
their dynamical status. We have performed MOIRCS observations of two high-z 
groups (z = 1.61 and 2.16) in our previous observations and identified 4-5 
massive quiescent galaxies in each system. Our MOIRCS spectra are not of 
suffcient quality for detailed absorption studies and we propose to observe 
these quiescent galaxies with the new, sensitive MOSFIRE. Our goal with the 
high quality spectra is to observationally constrain the formation timescale 
of massive cluster ellipticals by measuring spectral indices that are 
sensitive to different star formation time scales. We will also measure 
stellar velocity dispersion, which, when combined with our HST data, put 
constraints on the dynamical mass and 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.