Evolution of the star formation histories of BLAST galaxies

We have measured star formation histories (SFHs) and stellar masses of galaxies detected by the Balloon-borne Large Aperture Submillimetre Telescope (BLAST) over similar to 9 deg(2) centred on the Chandra Deep Field-South. We have applied the recently developed SFH reconstruction method of Dye et al. to optical, near-infrared and mid-infrared photometry of 92 BLAST galaxies. We find significant differences between the SFHs of low-mass (less than or similar to 10(11) M-circle dot) and high-mass (greater than or similar to 10(11) M-circle dot) systems. On average, low-mass systems exhibit a dominant late burst of star formation which creates a large fraction of their stellar mass. Conversely, high-mass systems tend to have a significant amount of stellar mass that formed much earlier. We also find that the high-mass SFHs evolve more strongly than the low-mass SFHs. These findings are consistent with the phenomenon of downsizing observed in optically selected samples of galaxies.