NGC 346 in the Small Magellanic Cloud. III. Recent Star Formation and Stellar Clustering Properties in the Bright HII Region N 66

TL;DR

This study analyzes the recent star formation and clustering of low-mass pre-main sequence stars in NGC 346/N 66 in the SMC, revealing multiple star formation events and self-similar clustering properties similar to Milky Way regions.

Contribution

It provides new insights into the age spread, spatial distribution, and clustering behavior of PMS stars in NGC 346, highlighting similarities with Milky Way star-forming regions despite different metallicities.

Findings

PMS stars are grouped in at least five clusters.

Clustering follows a power law with slope ~ -0.3.

Star formation may have occurred in two distinct events about 10 and 5 Myr ago.

Abstract

In the third part of our photometric study of the star-forming region NGC 346/N~66 and its surrounding field in the Small Magellanic Cloud (SMC), we focus on the large number of low-mass pre-main sequence (PMS) stars revealed by the Hubble Space Telescope Observations with the Advanced Camera for Surveys. We investigate the origin of the observed broadening of the pre-main sequence population in the $V-I$, $V$ CMD. The most likely explanations are either the presence of differential reddening or an age spread among the young stars. Assuming the latter, simulations indicate that we cannot exclude the possibility that stars in NGC 346 might have formed in two distinct events occurring about 10 and 5 Myr ago, respectively. We find that the PMS stars are not homogeneously distributed across NGC 346, but instead are grouped in at least five different clusters. On spatial scales from 0.8$''$ to 8$''$ (0.24 to 2.4 pc at the distance of the SMC) the clustering of the PMS stars as computed by a two-point angular correlation function is self-similar with a power law slope $\gamma \approx -0.3$. The clustering properties are quite similar to Milky Way star forming regions like Orion OB or $\rho$ Oph. Thus molecular cloud fragmentation in the SMC seems to proceed on the same spatial scales as in the Milky Way. This is remarkable given the differences in metallicity and hence dust content between SMC and Milky Way star forming regions.