The bursty star formation histories of low-mass galaxies at 0.4<z<1 revealed by star formation rates measured from Hβ and FUV

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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 Hβ and FUV (1500 Å) (Hβ-to-FUV ratio). Our sample contains 164 galaxies down to stellar mass (M*) of 10^(8.5) Mꙩ 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 Hβ- and FUV-derived SFRs is measured, dust extinction correction is negligible (except for very dusty galaxies) with the Calzetti attenuation curve. The Hβ-toFUV ratio of our sample increases with M* and SFR. The median ratio is ∼0.7 at M* ∼ ^(8.5) Mꙩ (or SFR ∼ 0.5 Me yr−1 ) and increases to ∼1 at M* ∼ 10^(10) Mꙩ (or SFR ∼ 10 Me yr−1 ). At M* < 10^(9.5) Mꙩ, our median Hβ-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 Hβ-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.
© 2016. The American Astronomical Society. Artículo firmado por 20 autores. We thank the anonymous referee for the valuable and constructive comments, which improve this article. Y.G., S.M. F., D.C.K., G.B., and H.Y. acknowledge support from NSF Grant AST-0808133. Support for Program HST-GO-12060 and HST-AR-13891 were provided by NASA through a grant from the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. MR acknowledges support from an appointment to the NASA Postdoctoral Program at Goddard Space Flight Center. Facilities: HST (WFC3), Keck (DEIMOS).
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