Evidence of Galactic Interaction in the Small Magellanic Cloud Probed by Gaia Selected Massive Star Candidates

TL;DR

This study uses Gaia DR3 data to identify and analyze the kinematics of massive stars in the Small Magellanic Cloud, revealing evidence of galactic interaction and tidal stretching caused by the Large Magellanic Cloud.

Contribution

It provides a comprehensive kinematic analysis of massive stars in the SMC, demonstrating inhomogeneous distributions and superstructures indicative of tidal interactions.

Findings

Massive stars are distributed in superstructures with distinct proper motions.

The superstructures exhibit opposite motions in the east and west, indicating tidal stretching.

Results suggest the SMC is being stretched by the LMC, not rotating.

Abstract

We present identifications and kinematic analysis of 7,426 massive ($\mathrm{\geq}8M_{\odot}$) stars in the Small Magellanic Cloud (SMC), using Gaia DR3 data. We used Gaia ($G_\mathrm{BP}-G_\mathrm{RP}$, $G$) color-magnitude diagram to select the population of massive stars, and parallax to omit foreground objects. The spatial distribution of the 7,426 massive star candidates is generally consistent with the spatial distribution of the interstellar medium, such as H$\alpha$ and H i emission. The identified massive stars show inhomogeneous distributions over the galaxy, showing several superstructures formed by massive stars with several hundred parsecs scale. The stellar superstructures defined by the surface density have opposite mean proper motions in the east and west, moving away from each other. Similarly, the mean line-of-sight velocities of the superstructures are larger to the southeast and smaller to the northwest. The different east-west properties of the superstructures' proper motion, line-of-sight velocity indicate that the SMC is being stretched by tidal forces and/or ram pressure from the Large Magellanic Cloud to the southeast, thereby rejecting the presence of galaxy rotation in the SMC.