Abstract

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 angstrom) (H beta-to-FUV ratio). Our sample contains 164 galaxies down to stellar mass (M-*) of 10(8.5) M-circle dot in the CANDELS GOODS-N region, where Team Keck Redshift Survey Keck/DEIMOS spectroscopy and Hubble Space Telescope/WFC3 F275W images from CANDELS and Hubble Deep UV Legacy Survey are available. When the 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-toFUV ratio of our sample increases with M-* and SFR. The median ratio is similar to 0.7 at M-* similar to 10(8.5) M-circle dot (or SFR similar to 0.5M(circle dot) yr(-1)) and increases to similar to 1 at M-* similar to 10(10) M-circle dot (or SFR similar to 10 M-circle dot yr(-1)). At M-* 10(9.5) M-circle dot, 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 for 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.