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

TL;DR

This study reveals that low-mass galaxies at redshifts 0.4 to 1 exhibit bursty star formation histories, with the burstiness increasing as galaxy mass decreases, based on Hβ and FUV star formation rate ratios.

Contribution

It provides observational evidence for bursty star formation in low-mass galaxies at intermediate redshifts using Hβ and FUV measurements, highlighting the evolution of star formation variability.

Findings

Hβ--to--FUV ratio increases with galaxy mass and SFR.

Lower ratios at low masses suggest more bursty SFHs compared to local galaxies.

Burstiness is more significant in less massive galaxies.

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 \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.