PI: Chun Ly, U. of Arizona, firstname.lastname@example.org
Address: Department of Astronomy and Steward Observatory, 933 NORTH CHERRY AVENUE, TUCSON, AZ 85721-0065 USA
CoI: Matthew A Malkan, UCLA
Title: Recalibrating Strong-line Metallicity Diagnostics for z>1 Chemical Enrichment Studies, with T_e-based Metallicities from MACT and DEEP2
Abstract: -- This is a re-submission of our previously approved 2017A program, which suffered from significant sensitivity degradation due to an issue with the instrument. -- The gas-phase metallicity of galaxies---and how it depends on stellar mass and SFR---is a key test of galaxy evolution models with accretion and star-formation ``feedback.'' However, tracing the evolution of the stellar mass--metallicity--SFR relation has been problematic since local "strong-line" metallicity diagnostics are _not_ valid for high-redshift galaxies. To directly address this, electron temperature (T_e) based metallicities at high redshifts are necessary to recalibrate metallicity diagnostics. This is challenging as it requires the detection of [OIII]4363. We have detected [OIII]4363 in ~100 star-forming galaxies at redshifts up to z~1. However, existing optical spectra miss H-alpha and [NII]6583 at z>0.5. These emission lines are used in almost _all_ chemical enrichment studies. We propose GNIRS spectroscopy of 14 z~1 [OIII]4363-detected galaxies, to recalibrate strong-line metallicity diagnostics using T_e-based metallicities. Our program efficiently uses telescope time by targeting galaxies that already have nebular emission-line measurements below rest-frame ~5010 Angstroms. Also, we have found that these galaxies have similar ISM properties as z>2 galaxies. Our measurements will be incorporated within our existing framework for metallicity recalibration, which we are already finding to be more robust than previous calibrations. Given the importance of strong-line metallicity diagnostics, our new calibration will be frequently used in chemical enrichment studies.
Program Type: Standard/Extragalactic
Run 1 (2018A): GEM-NQ/GNIRS -- 15hrs band 2 (GN-2018A-Q-217 )
National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360