Progressive star formation in the young galactic super star cluster NGC 3603

TL;DR

This study uses HST observations to analyze the recent star formation history of NGC 3603, revealing ongoing star formation for at least 10-20 million years with a median age of 3 million years among PMS stars.

Contribution

It provides the first clear evidence that star formation in NGC 3603 has been continuous for over 10 million years, based on Halpha excess emission analysis.

Findings

2/3 of PMS stars are 1-10 Myr old

1/3 of PMS stars are older than 10 Myr

Star formation has been ongoing for at least 10-20 Myr

Abstract

Early release science observations of the cluster NGC3603 with the WFC3 on the refurbished HST allow us to study its recent star formation history. Our analysis focuses on stars with Halpha excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with Halpha excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.