(Proposal ID) S14B-152

(PI) Onodera Masato

(Proposal Title)
 Fundamental metallicity relation at z>3: Are galaxies gas-regulated systems?

(Abstract)
This proposal is a resubmission of an accepted proposal S13B-088 in which we 
got no data due to bad weather. Star-forming galaxies in the local Universe 
are known to lie on a tight surface in the stellar mass (M_*)-star formation 
rate (SFR)-metallicity (Z) space, with a strikingly small scatter of 0.05 dex. 
Studies of the Z(M_*,SFR) have suggested it may be constant to z~2.5 even as 
the SFR at given mass increases by a factor of twenty --- leading to the idea 
of a "fundamental metallicity relation'' (FMR). There is some observational 
evidence for a change in behavior at z>3. Theoretically, a simple model of 
star-formation in galaxies naturally reproduces the form and constancy of the 
FMR. However, this gas-regulated system may break down at very high redshifts 
because of the convergence of a number of timescales.  Here we propose a 
Keck/MOSFIRE spectroscopy for ~50 galaxies at 3<z_{spec}<3.8 to measure 
metallicities in order to study the Z(M*,SFR) relation at z>3 across a wide 
range of M_* and SFR yet being explored. Using metallicities and SFRs from 
the emission lines, and M_* from SED fitting, we will investigate the 
existence and form of Z(M_*,SFR) at z>3 in detail and thereby gain new 
insights into the flow of gas into and out of galaxies at high redshifts.