"Direct" Gas-Phase Metallicity in Local Analogs of High-Redshift
  Galaxies: Empirical Metallicity Calibrations for High-Redshift Star-Forming
  Galaxies
  We study the direct gas-phase oxygen abundance using the well-detected
auroral [OIII]4363 line in the stacked spectra of a sample of local analogs of
high-redshift galaxies. These local analogs share the same location as $z\sim2$
star-forming galaxies on the Baldwin-Phillips-Terlevich diagram. This type of
analog has the same ionized interstellar medium (ISM) properties as
high-redshift galaxies. We establish empirical metallicity calibrations between
the direct gas-phase oxygen abundances ($7.8<12+\log(\rm{O/H})<8.4$) and the
N2/O3N2 indices in our local analogs. We find significant systematic offsets
between the metallicity calibrations for our local analogs of high-redshift
galaxies and those derived from the local HII regions and a sample of local
reference galaxies selected from the Sloan Digital Sky Survey (SDSS). The N2
and O3N2 metallicities will be underestimated by 0.05-0.1~dex relative to our
calibration if one simply applies the local metallicity calibration in previous
studies to high-redshift galaxies. Local metallicity calibrations also cause
discrepancies of metallicity measurements in high-redshift galaxies using the
N2 and O3N2 indicators. In contrast, our new calibrations produce consistent
metallicities between these two indicators. We also derive metallicity
calibrations for R23, O32, log([OIII]/H\beta), and log([NeIII]/[OII]) indices
in our local analogs, which show significant offset compared to those in the
SDSS reference galaxies. By comparing with MAPPINGS photoionization models, the
different empirical metallicity calibration relations in the local analogs and
the SDSS reference galaxies can be shown to be primarily due to the change of
ionized ISM conditions.
