The Star Formation Burstiness and Ionizing Efficiency of Low-mass
  Galaxies
  We investigate the burstiness of star formation and the ionizing efficiency
of a large sample of galaxies at $0.7 < z < 1.5$ using HST grism spectroscopy
and deep ultraviolet (UV) imaging in the GOODS-N and GOODS-S fields. The star
formation history (SFH) in these strong emission line low-mass galaxies
indicates an elevated star formation rate (SFR) based on the H$\alpha$ emission
line at a given stellar mass when compared to the standard main sequence.
Moreover, when comparing the H$\alpha$ and UV SFR indicators, we find that an
excess in SFR(H$\alpha$) compared to SFR(UV) is preferentially observed in
lower-mass galaxies below $10^{9}$ M$\odot$, which are also the highest-EW
galaxies. These findings suggest that the burstiness parameters of these strong
emission line galaxies may differ from those inferred from hydrodynamical
simulations and previous observations. For instance, a larger burstiness duty
cycle would explain the observed SFR(H$\alpha$) excess. We also estimate the
ionizing photon production efficiency $\xi_{ion}$, finding a median value of
Log($\xi_{ion}$/erg$^{-1}$ Hz)$=24.80 \pm 0.26$ when adopting a Galactic dust
correction for H$\alpha$ and an SMC one for the stellar component. We observe
an increase of $\xi_{ion}$ with redshift, further confirming similar results at
higher redshifts. We also find that $\xi_{ion}$ is strongly correlated with
EW(H$\alpha$), which provides an approach for deriving $\xi_{ion}$ in early
galaxies. Lower-mass, lower-luminosity galaxies have a higher $\xi_{ion}$.
Overall, these results provide further support for faint galaxies playing a
major role in the reionization of the Universe.
