Revisiting a detached stellar structure in the outer north-eastern region of the Small Magellanic Cloud

Abstract

The outer north-eastern region of the Small Magellanic Cloud (SMC) is populated by a shell-like overdensity whose nature was recently investigated. We analysed 20 catalogued star clusters projected on to it from Survey of the MAgellanic Stellar History data sets. After carrying out a cleaning of field stars in the star cluster colour-magnitude diagrams (CMDs), and deriving their astrophysical properties from a comparison between the observed and synthetic CMDs, we found that four objects are not genuine star clusters, while the remaining ones are young star clusters (11, age 30-200 Myr) and intermediate-age (5, age 1.7-2.8 Gyr) star clusters, respectively. The resulting distances show that intermediate-age and some young star clusters belong to the SMC main body, while the remaining young star clusters are nearly 13.0 kpc away from those in the SMC, revealing that the shell-like overdensity is more extended along the line of sight than previously thought. We also found a clear age trend and a blurred metallicity correlation along the line of sight of young clusters, in the sense that the farther a star cluster is from the SMC, the younger, the more metal-rich, and the less massive it is. These young clusters are also affected by a slightly larger interstellar reddening than the older ones in the shell-like overdensity. These outcomes suggest that the shell-like overdensity can possibly be another tidally perturbed/formed SMC stellar structure from gas stripped off its body, caused by the interaction with the Large Magellanic Cloud or the Milky Way.