HETDEX Pilot Survey. VI. [OIII] Emitters and Expectations for a Local
  Sample of Star Forming Galaxies in HETDEX
  We assemble an unbiased sample of 29 galaxies with [O II] $\lambda 3727$
and/or [O III] $\lambda 5007$ detections at $z < 0.15$ from the Hobby-Eberly
Telescope Dark Energy Experiment (HETDEX) Pilot Survey (HPS). HPS finds
galaxies without pre-selection based on their detected emission lines via
integral field spectroscopy. Sixteen of these objects were followed up with the
second-generation, low resolution spectrograph (LRS2) on the upgraded
Hobby-Eberly Telescope. Oxygen abundances were then derived via strong emission
lines using a Bayesian approach. We find most of the galaxies fall along the
mass-metallicity relation derived from photometrically selected star forming
galaxies in the Sloan Digital Sky Survey (SDSS). However, two of these galaxies
have low metallicity (similar to the very rare green pea galaxies in
mass-metallicity space). The star formation rates of this sample fall in an
intermediate space between the SDSS star forming main sequence and the extreme
green pea galaxies. We conclude that spectroscopic selection fills part of the
mass-metallicity-SFR phase space that is missed in photometric surveys with
pre-selection like SDSS, i.e., we find galaxies that are actively forming stars
but are faint in continuum. We use the results of this pilot investigation to
make predictions for the upcoming unbiased, large spectroscopic sample of local
line emitters from HETDEX. With the larger HETDEX survey we will determine if
galaxies selected spectroscopically without continuum brightness pre-selection
have metallicities that fall on a continuum that bridges typical star forming
and rarer, more extreme systems like green peas.
