(Proposal ID) S16B-006

(PI) Tanaka, Masayuki

(Proposal Title)
The Size-Mass Relation of Quiescent Galaxies at z~4

(Abstract)
{This is re-submission of our previously accepted program S15B-025 but lost to 
poor conditions (natural seeing >1".0 in K).} Recent observations have revealed
 that galaxies undergo a factor of ~3 growth in size since z~2. Quiescent 
galaxies at z~2 are surprisingly compact (r_{eff} ~ 1-2kpc) and dense and this 
has been a challenge to our framework of galaxy formation.  So far, the 
size-mass relation of galaxies up to z~2 has been the focus of the field, but 
one of the promising way to make a step forward is to go up to even higher 
redshifts. We have identified a number of massive (~10^{11} M_sun) quiescent 
galaxies at z~4 in UDS and COSMOS. Public HST/WFC3 images have revealed their 
extremely small sizes; r_{eff} ~ 0.05 arcsec or 0.35 kpc. However, this size 
is well below the pixel size of WFC3 and higher angular resolution 
observations are crucial for reliable size measurements. Here we propose to 
conduct an LGSAO+IRCS observation to achieve HWHM~0.05 arcsec, which should be 
sufficient to resolve r_{eff} < 0.05 arcsec for high S/N objects. We aim to 
measure accurate sizes of 9 quiescent galaxies and establish the size-mass 
relation at z~4 for the first time.  We will also characterize morphology and 
examine if the Hubble sequence already emerged at z~4.