The southern leading and trailing wraps of the Sagittarius tidal stream around the globular cluster Whiting1

TL;DR

This study analyzes the kinematics of stars around Whiting1, revealing two wraps of the Sagittarius tidal stream with distinct velocities, supporting the cluster's origin in Sagittarius and providing evidence for the stream's leading arm.

Contribution

It provides observational evidence of the leading wrap of the Sagittarius stream in the southern hemisphere, supporting models of its orbit and evolution.

Findings

Identification of two velocity components consistent with Sagittarius stream wraps.

Support for Whiting1's formation in Sagittarius and recent accretion.

Detection of the old leading wrap of Sagittarius in the southern hemisphere.

Abstract

We present a study of the kinematics of 101 stars observed with VIMOS around Whiting1, a globular cluster embedded in the Sagittarius tidal stream. The obtained velocity distribution shows the presence of two wraps of that halo substructure at the same heliocentric distance as that of the cluster and with well differentiated mean radial velocities. The most prominent velocity component seems to be associated with the trailing arm of Sagittarius with $<v_{\rm r}>$ ~ -130 km/s, which is consistent with the velocity of Whiting1. This result supports that this globular cluster was formed in Sagittarius and recently accreted by the Milky Way. The second component with $<v_{\rm r}>$ ~ 120 km/s might correspond to the leading arm of Sagittarius, which has been predicted by numerical simulations but with no conclusive observational evidence of its existence presented so far. This detection of the old leading wrap of Sagittarius in the southern hemisphere may be used to confirm and further constrain the models for its orbit and evolution.