The ACS Nearby Galaxy Survey Treasury V. Radial Star Formation History of NGC 300

TL;DR

This study uses HST observations to analyze the star formation history and radial growth of NGC 300, revealing inside-out disk growth and minimal radial migration effects.

Contribution

It provides the first detailed radial star formation history of NGC 300, demonstrating inside-out growth and contrasting its evolution with similar galaxies like M33.

Findings

The stellar disk is predominantly old out to 5.4 kpc.

The disk's scale length increased from 1.1 to 1.3 kpc over 10 Gyr.

Radial migration effects are minimal in NGC 300.

Abstract

We present new Hubble Space Telescope (HST) observations of NGC 300 taken as part of the ACS Nearby Galaxy Survey Treasury (ANGST). Individual stars are resolved in these images down to an absolute magnitude of M_F814W = 1.0 (below the red clump). We determine the star formation history of the galaxy in 6 radial bins by comparing our observed color-magnitude diagrams (CMDs) with synthetic CMDs based on theoretical isochrones. We find that the stellar disk out to 5.4 kpc is primarily old, in contrast with the outwardly similar galaxy M33. We determine the scale length as a function of age and find evidence for inside-out growth of the stellar disk: the scale length has increased from 1.1 +/- 0.1 kpc 10 Gyr ago to 1.3 +/- 0.1 kpc at present, indicating a buildup in the fraction of young stars at larger radii. As the scale length of M33 has recently been shown to have increased much more dramatically with time, our results demonstrate that two galaxies with similar sizes and morphologies can have very different histories. With an N-body simulation of a galaxy designed to be similar to NGC 300, we determine that the effects of radial migration should be minimal. We trace the metallicity gradient as a function of time and find a present day metallicity gradient consistent with that seen in previous studies. Consistent results are obtained from archival images covering the same radial extent but differing in placement and filter combination.