(Proposal ID) S17B-106

(PI) Tanaka, Masayuki

(Proposal Title)
Direct Spectroscopic Confirmation of z>4 Quiescent Galaxies

(Abstract)
We propose to carry out deep near-IR spectroscopy of massive quiescent galaxies
at z>4 with MOSFIRE. Recently, Glazebrook et al. demonstrated that MOSFIRE can 
detect absorption line features in bright quiescent galaxies at z=3.7. We have 
even better candidates at higher redshifts, carefully selected from deep multi-
wavelength data in UDS and COSMOS. Because we will cover the entire 4000 
Angstrom break feature in the K-band for our targets, we will be able to 
measure the detailed continuum shape as well as absorption lines, which will 
give a very tight constraint on the stellar age and stellar mass to luminosity 
ratios. Glazebrook et al's object is at a too low redshift and did not probe 
the break feature, resulting in somewhat poor constraints on the stellar age. 
Our observation will thus be the first one to measure the detailed stellar 
populations of the quiescent galaxies at z>4. As the universe is only 1.5 Gyr 
old, the derived stellar age will place an extremely strong constraint on both 
the formation and quenching timescales of massive galaxies at high redshifts. 
As a byproduct, we will break the record of the highest redshift quiescent 
galaxy with spectroscopic confirmation.