(Proposal ID) S17A-169

(PI) Chiang, Yi-Kuan

(Proposal Title)
JWST High-z Pathfinder: 3D-HST Metal Poor Galaxies at z~0.8

(Abstract)
We propose deep DEIMOS spectroscopy of R_{23} metallicity diagnostics for ~180 
metal poor galaxy (MPG) candidates in 3D-HST at z ~ 0.8. High-z MPGs are 
crucial to study the onset of galaxy formation. With the upcoming JWST, strong 
line diagnostics can be performed up to z~9. However, systematic MPG search is 
still in its infancy even right beyond z~0. We develop a simple, unbiased, 
widely applicable MPG selection with the metallicity predicted by stellar mass 
and star formation seen in the continuum. Using 3D-HST grism spectra and 
photometry, we select a candidate MPG sample of 1/5--1/30 solar abundance. 
To confirm these metallicity predictions we will take deep (5 hrs) R~3300 
spectra in 6000 Angstrom--1 mu m for ~180 galaxies in two masks. The wide 
wavelength coverage allows R_{23} diagnostics in a single grating setup. This 
program will deliver >10 times larger, high quality MPG sample at z~0.8. We 
will put strong constraint on the environment of MPGs utilizing 3D-HST's dense 
galaxy mapping. The global distribution of [OIII]/[OII] ratio will be censused 
with our unbiased sample constraining the ionization conditions of MPGs. 
Timely completion of this pathfinder program will support Japanese community 
in competing the first JWST call.