3D kinematics of Small Magellanic Cloud star clusters: Residual velocities disentangle kinematically perturbed clusters

¹ Instituto Interdisciplinario de Ciencias Básicas (ICB), CONICET-UNCuyo, Padre J. Contreras 1300, M5502JMA, Mendoza, Argentina
² Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Godoy Cruz 2290, C1425FQB, Buenos Aires, Argentina

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 25 September 2025
Accepted: 9 April 2026

Abstract

Understanding the kinematic behavior of the Small Magellanic Cloud (SMC) remains a challenge addressed by many authors using diverse approaches. Over time, increasing observational evidence has accumulated for tidal perturbations induced by the Large Magellanic Cloud (LMC) on the SMC, especially in its outer regions. In this study, we adopted star clusters as kinematic tracers of the SMC. We analyzed 36 clusters distributed across the galaxy's structural regions (Northern Bridge, Southern Bridge, Wing/Bridge, West Halo, Main Body and Counter Bridge). From each cluster's proper motions, radial velocity, and heliocentric distance, we estimated Cartesian velocities (V_x, V_y, V_z) in the SMC reference frame. We also computed the same velocity components under the assumption that the SMC behaves as a rotating disk. We then defined the residual velocity ΔV for each cluster as the difference between the two derived velocities. Additionally, we performed kinematic anisotropy analysis to characterize the distribution of kinetic energy across the SMC. We find that increasing values of ΔV correlate with increasing cluster distance from the SMC center, and that ΔV ≈ 60 km s⁻¹ appears to be a kinematic lower limit separating the tidally originating areas from those with the best behavior.