An in-depth view of the metallicity distribution of the Small Magellanic Cloud

TL;DR

This study investigates the metallicity distribution of star clusters in the Small Magellanic Cloud, revealing that actual spatial distances alter previous gradient interpretations and showing a shallow, age-dependent metallicity gradient with regional variations.

Contribution

The paper demonstrates the importance of using actual distances over projected ones in analyzing metallicity gradients and provides new insights into the age-related and regional metallicity distribution in the SMC.

Findings

Bimodal metallicity distribution and V-shaped gradient fade with actual distances.

Older clusters (>1 Gyr) show a shallow metallicity gradient.

Clusters beyond 11 kpc in the eastern galaxy have distinct metallicity properties.

Abstract

The spatial metallicity distribution of star clusters in the Small Magellanic Cloud (SMC) has recently been found to correlate as a V-shaped function with the semi-major axis of an elliptical framework proposed to assume a projected galaxy flattening. We report results on the impact that the use of such a framework can produce on our understanding of the SMC formation and its chemical enrichment. We show that clusters with similar semi-major axes are placed at a very different distances from the SMC centre. The recently claimed bimodal metallicity distribution of clusters projected on the innermost SMC regions and the V-shaped metallicity gradient fade away when actual distances are used. Although a large dispersion prevails, clusters older than $\sim$ 1 Gyr exhibit a shallow metallicity gradient, caused by slightly different spatial distributions of clusters younger and older than $\sim$ 4 Gyr; the former being more centrally concentrated and having a mean metallicity ([Fe/H]) $\sim$ 0.15 dex more metal-rich than that of older clusters. This metallicity gradient does not show any dependence with the position angle, except for clusters placed beyond 11 kpc, which are located in the eastern side of the galaxy.