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

TL;DR

This study reconstructs the star formation history of nearby galaxy disks, revealing a decline since z~1 and highlighting differences in recent star formation rates between galaxy types.

Contribution

It provides a comprehensive star formation history for a volume-limited sample of galaxies using ACS data, including dwarf and spiral galaxies, and compares results with other techniques.

Findings

Star formation rate density drops by a factor of ~3 at z~2.

Recent star formation rates are higher than previous estimates.

About 50% of stellar mass in dwarfs and spirals formed by z>~2.

Abstract

We present a measurement of the age distribution of stars residing in spiral disks 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 Advanced Camera for Surveys (ACS) Nearby Galaxy Survey Treasury (ANGST). The total star formation rate 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 formation rate 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 formation rate appears to be largely due to an increase in the fraction of star formation contained 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 mass in dwarf galaxies was similar to that of ~50% of the stellar mass in large spiral galaxies (z>~2), despite the observed galaxy-to-galaxy diversity among the dwarfs.