The outer structure of old star clusters in the Small Magellanic Cloud

Abstract

We report results on the internal dynamical evolution of old star clusters located in the outer regions of the Small Magellanic Cloud (SMC). Because the SMC has been im- printed with evidence of tidal interaction with the Large Magellanic Cloud (LMC), we investigated at what extend such an interaction has produced extra tidal structures or excess of stars beyond the clusters’ tidal radii. For that purpose, we used the Survey of the Magellanic Stellar History (SMASH) DR2 data sets to build number density radial profiles of suitable star clusters, and derived their structural and internal dynamics parameters. The analysed stellar density profiles do not show any evidence of tidal ef- fects caused by the LMC. On the contrary, the Jacobi volume of the selected SMC star clusters would seem underfilled, with a clear trend toward a smaller percentage of un- derfilled volume as their deprojected distance to the SMC centre increases. Moreover, the internal dynamical evolution of SMC star clusters would seem to be influenced by the SMC gravitational field, being star clusters located closer to the SMC centre in a more advanced evolutionary stage. We compared the internal dynamical evolution of SMC old star clusters with those of LMC and Milky Way globular clusters, and found that Milky Way globular clusters have dynamical evolutionary paths similar to LMC/SMC old star clusters located closer to their respective galaxy’s centres. Finally, we speculate with the possibility that globular clusters belonging to Magellanic Clouds like-mass galaxies have lived a couple of times their median relaxation times.