The retrograde orbit of the globular cluster FSR1758 revealed with Gaia DR2

Understand

We report the first radial velocity measurements of the recently identified globular cluster FSR1758.

• From the two member stars with radial velocities from the Gaia Radial Velocity Spectrograph reported in Gaia DR2, we find FSR1758 has a radial velocity of $227\pm1$ km/s.
• We also find potential extra-tidal star lost from the cluster in the surrounding 1~deg.
• Combined with Gaia proper motions and photometric distance estimates, this shows that FSR1758 is on a very retrograde, radial orbit with an pericentre of $3.8_{-0.9}^{+0.9}$ kpc, an apocentre of $16_{-5}^{+8}$ kpc, and eccentricity of $0.62_{-0.04}^{+0.05}$.