The History of Star Formation in Galaxy Disks in the Local Volume as Measured by the ACS Nearby Galaxy Survey Treasury

We present a measurement of the age distribution of stars residing in spiral disks and dwarf galaxies. We derive a complete star formationhistory of the ~140 Mpc^3 covered by the volume-limited sample of galaxiesin the Advanced Camerafor Surveys(ACS) Nearby GalaxySurvey Treasury (ANGST). The total star formationrate density history is dominated by the large spirals in the volume, although the sample consists mainly of dwarf galaxies. Our measurement shows a factor of ~3 drop at z~2, in approximate agreement with results from other measurement techniques. While our results show that the overall star formationrate density has decreased since z~1, the measured rates during this epoch are higher than those obtained from other measurement techniques. This enhanced recent star formationrate appears to be largely due to an increase in the fraction of star formationcontained in low-mass disks at recent times. Finally, our results indicate that despite the differences at recent times, the epoch of formation of ~50% of the stellar massin dwarf galaxieswas similar to that of ~50% of the stellar massin large spiral galaxies(z>~2), despite the observed galaxy-to- galaxydiversity among the dwarfs.