The AURORA Survey: First Direct Metallicity Calibrations at High Redshift

We propose the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) program, which will obtain ultra-deep and continuous R=1000 NIRSpec MSA spectroscopy over the wavelength range 1-5 microns using the G140M/F100LP, 235M/F170LP, G395M/F290LP gratings. We will collect spectra of ~100 galaxies in two carefully chosen pointings, one in each of the COSMOS and GOODS-N extragalactic legacy fields. Target selection will be optimized to obtain the first statistical sample of ~45 z=1.5- 4.0 galaxies with detectable auroral emission lines enabling direct oxygen abundance estimates. With these measurements, representing an order-of-magnitude increase in the sample of direct oxygen abundances at z>=1.5, we will construct the first empirical strong-line metallicity calibrations at high redshift. Such calibrations are essential for exploiting the transformative rest-frame optical emission-line datasets to be collected with JWST/NIRspec out to z~10, and measuring actual oxygen abundances rather than simply the ratios of strong nebular emission lines. In turn, measurements of galaxy chemical abundances over cosmic time, in concert with their stellar masses, provide critical constraints on galaxy formation models. Using the proposed ultra-deep near-IR spectroscopic observations, we will also explore the physical properties of gas and stars in z>6 star-forming galaxies during the epoch of reionization, calibrate the nebular attenuation curve during the epoch of peak star formation (z=1.5-4.0), and constrain the formation histories of massive, quiescent galaxies.