The interstellar medium in [OIII]-selected star-forming galaxies at
  $z\sim3.2$
  We present new results from near-infrared spectroscopy with Keck/MOSFIRE of
[OIII]-selected galaxies at $z\sim3.2$. With our $H$ and $K$-band spectra, we
investigate the interstellar medium (ISM) conditions, such as ionization states
and gas metallicities. [OIII] emitters at $z\sim3.2$ show a typical gas
metallicity of $\mathrm{12+log(O/H) = 8.07\pm0.07}$ at
$\mathrm{log(M_*/M_\odot) \sim 9.0-9.2}$ and $\mathrm{12+log(O/H) =
8.31\pm0.04}$ at $\mathrm{log(M_*/M_\odot) \sim 9.7-10.2}$ when using the
empirical calibration method. We compare the [OIII] emitters at $z\sim3.2$ with
UV-selected galaxies and Ly$\alpha$ emitters at the same epoch and find that
the [OIII]-based selection does not appear to show any systematic bias in the
selection of star-forming galaxies. Moreover, comparing with star-forming
galaxies at $z\sim2$ from literature, our samples show similar ionization
parameters and gas metallicities as those obtained by the previous studies
using the same calibration method. We find no strong redshift evolution in the
ISM conditions between $z\sim3.2$ and $z\sim2$. Considering that the star
formation rates at a fixed stellar mass also do not significantly change
between the two epochs, our results support the idea that the stellar mass is
the primary quantity to describe the evolutionary stages of individual galaxies
at $z>2$.
