Neighbors, Not Kin: Kinematic evidence for tidal tails from NGC 7492 along the Sagittarius stream

Abstract

The formation, extension, and morphology of extra-tidal stars around globular clusters depend on the internal kinematics of the host cluster and the Galactic potential. Tracing the kinematics of faint tidal tails sheds light on their formation and contribution to the Milky Way halo. NGC 7492 is an outer halo globular cluster with conflicting evidence regarding the presence of tidal tails. If present, the tails are expected to be faint and overlap on the sky with the Sagittarius stream, located at a similar heliocentric distance but with distinct kinematics. We carried out a GIRAFFE spectroscopic follow-up of ten fields covering the expected tidal tails of NGC 7492. Gaia parallaxes were used to remove foreground contaminants, while only loose proper-motion constraints were applied in the target selection. Radial velocities and metallicities were derived for more than 700 stars, from the red giant branch to the upper main sequence. Cluster and extra-tidal stars were identified from their proper motions, radial velocities, and metallicities. This population extends at least 1.8 deg from the cluster center, confirming the tidal tails previously detected only photometrically, with positions consistent with particle-spray models of the cluster disruption. The Sagittarius stream is clearly identified through its distinct proper motions, radial velocities, and more metal-rich population. Despite the low spatial density of the extra-tidal stars, their kinematic signature is clearly detected, demonstrating that the tidal tails overlap on the sky with the Sagittarius stream but are physically unrelated. This spectroscopic dataset provides a robust basis for future studies of the tails at larger angular extents and fainter magnitudes.