The Bursty Star Formation Histories of Low-mass Galaxies at $0.4<z<1$
  Revealed by Star Formation Rates Measured from H$\beta$ and FUV
  We investigate the burstiness of star formation histories (SFHs) of galaxies
at $0.4<z<1$ by using the ratio of star formation rates (SFRs) measured from
H$\beta$ and FUV (1500 \AA) (H$\beta$--to--FUV ratio). Our sample contains 164
galaxies down to stellar mass (M*) of $10^{8.5} M_\odot$ in the CANDELS GOODS-N
region, where Team Keck Redshift Survey DEIMOS spectroscopy and HST/WFC3 F275W
images from CANDELS and Hubble Deep UV Legacy Survey are available. When the
{\it ratio} of H$\beta$- and FUV-derived SFRs is measured, dust extinction
correction is negligible (except for very dusty galaxies) with the Calzetti
attenuation curve. The H$\beta$--to--FUV ratio of our sample increases with M*
and SFR. The median ratio is $\sim$0.7 at M*$\sim10^{8.5} M_\odot$ (or SFR$\sim
0.5 M_\odot/yr$) and increases to $\sim$1 at M*$\sim10^{10} M_\odot$ (or SFR
$\sim 10 M_\odot/yr$). At M*$<10^{9.5} M_\odot$, our median H$\beta$--to--FUV
ratio is lower than that of local galaxies at the same M*, implying a redshift
evolution. Bursty SFH on a timescale of a few tens of megayears on galactic
scales provides a plausible explanation of our results, and the importance of
the burstiness increases as M* decreases. Due to sample selection effects, our
H$\beta$--to--FUV ratio may be an upper limit of the true value of a complete
sample, which strengthens our conclusions. Other models, e.g., non-universal
initial mass function or stochastic star formation on star cluster scales, are
unable to plausibly explain our results.
