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We present evidence for stochastic star formation histories in low-mass (M* <10^10 Msun) galaxies from observations within the Galaxy And Mass Assembly(GAMA) survey. For ~73,000 galaxies between 0.05<z<0.32, we calculate starformation rates (SFR) and specific star formation rates (SSFR = SFR/M*) fromspectroscopic Halpha measurements and apply dust corrections derived fromBalmer decrements. We find a dependence of SSFR on stellar mass, such thatSSFRs decrease with increasing stellar mass for star-forming galaxies, and forthe full sample, SSFRs decrease as a stronger function of stellar mass. We usesimple parametrizations of exponentially declining star formation histories toinvestigate the dependence on stellar mass of the star formation timescale andthe formation redshift. We find that parametrizations previously fit to samplesof z~1 galaxies cannot recover the distributions of SSFRs and stellar massesobserved in the GAMA sample between 0.05<z<0.32. In particular, a large numberof low-mass (M* < 10^10 Msun) galaxies are observed to have much higher SSFRsthan can be explained by these simple models over the redshift range of0.05<z<0.32, even when invoking mass-dependent staged evolution. For such alarge number of galaxies to maintain low stellar masses, yet harbour such highSSFRs, requires the late onset of a weak underlying exponentially declining SFHwith stochastic bursts of star formation superimposed.

Galaxy And Mass Assembly (GAMA): Linking Star Formation Histories and Stellar Mass Growth