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

摘要

We present a measurement of the age distribution of stars residing in spiraldisks and dwarf galaxies. We derive a complete star formation history of the~140 Mpc^3 covered by the volume-limited sample of galaxies in the AdvancedCamera for Surveys (ACS) Nearby Galaxy Survey Treasury (ANGST). The total starformation rate density history is dominated by the large spirals in the volume,although the sample consists mainly of dwarf galaxies. Our measurement shows afactor of ~3 drop at z~2, in approximate agreement with results from othermeasurement techniques. While our results show that the overall star formationrate density has decreased since z~1, the measured rates during this epoch arehigher than those obtained from other measurement techniques. This enhancedrecent star formation rate appears to be largely due to an increase in thefraction of star formation contained in low-mass disks at recent times.Finally, our results indicate that despite the differences at recent times, theepoch of formation of ~50% of the stellar mass in dwarf galaxies was similar tothat of ~50% of the stellar mass in large spiral galaxies (z>~2), despite theobserved galaxy-to-galaxy diversity among the dwarfs.