Star Formation History of the SMC: six HST/ACS

TL;DR

This study used HST/ACS observations of six SMC fields to analyze its star formation history, revealing early star formation, chemical enrichment variations, and recent localized star formation activity.

Contribution

It provides detailed spatially-resolved star formation history of the SMC using deep HST imaging, highlighting variations over time and across regions.

Findings

SMC started forming stars ~12 Gyr ago.

Outer regions have lower metallicity than central areas.

Recent star formation increased in the last 500 Myr, especially in the bar and wing.

Abstract

We observed six fields of the Small Magellanic Cloud (SMC) with the Advanced Camera for Survey on board the Hubble Space Telescope in the F555W and F814W filters. These fields sample regions characterized by very different star and gas densities, and, possibly, by different evolutionary histories. We find that the SMC was already forming stars ~12 Gyr ago, even if the lack of a clear horizontal branch suggests that in the first few billion years the star formation activity was low. Within the uncertainties of our two-band photometry, we find evidence of a radial variation in chemical enrichment, with the SMC outskirts characterized by lower metallicity than the central zones. From our CMDs we also infer that the SMC formed stars over a long interval of time until ~2-3 Gyr ago. After a period of modest activity, star formation increased again in the recent past, especially in the bar and the wing of the SMC, where we see an enhancement in the star-formation activity starting from ~500 Myr ago. The inhomogeneous distribution of stars younger than ~100 Myr indicates that recent star formation has mainly developed locally.