Structural Parameters of Seven SMC Intermediate-Age and Old Star Clusters

TL;DR

This study analyzes the structural parameters of seven intermediate-age and old star clusters in the Small Magellanic Cloud, revealing how their core radii and shapes evolve with age and internal processes.

Contribution

It provides detailed structural profiles of SMC clusters using Hubble data and compares their properties across different ages and locations within the galaxy.

Findings

Older clusters have larger core radii, increasing with age.

No evidence of post core collapse clusters was found.

Cluster ellipticity shows no correlation with distance from the SMC center.

Abstract

We present structural parameters for the seven intermediate-age and old star clusters NGC121, Lindsay 1, Kron 3, NGC339, NGC416, Lindsay 38, and NGC419 in the Small Magellanic Cloud. We fit King profiles and Elson, Fall, and Freeman profiles to both surface-brightness and star count data taken with the Advanced Camera for Surveys aboard the Hubble Space Telescope. Clusters older than 1 Gyr show a spread in cluster core radii that increases with age, while the youngest clusters have relatively compact cores. No evidence for post core collapse clusters was found. We find no correlation between core radius and distance from the SMC center, although consistent with other studies of dwarf galaxies, some relatively old and massive clusters have low densities. The oldest SMC star cluster, the only globular NGC121, is the most elliptical object of the studied clusters. No correlation is seen between ellipticity and distance from the SMC center. The structures of these massive intermediate-age (1-8 Gyr) SMC star clusters thus appear to primarily result from internal evolutionary processes.