Evidence for Substructure in Ursa Minor Dwarf Spheroidal Galaxy using a Bayesian Object Detection Method

Understand

We present a method for identifying localized secondary populations in stellar velocity data using Bayesian statistical techniques.

• We apply this method to the dwarf spheroidal galaxy Ursa Minor and find two secondary objects in this satellite of the Milky Way.
• One object is kinematically cold with a velocity dispersion of $4.25 \pm 0.75\ \kms$ and centered at $(9.1\arcmin \pm 1.5, 7.2\arcmin \pm 1.2)$ in relative RA and DEC with respect to the center of Ursa Minor.
• The second object has a large velocity offset of $-12.8^{+1.75}_{-1.5}\ \kms$ compared to Ursa Minor and centered at $(-14.0\arcmin^{+2.4}_{-5.8}, -2.5\arcmin^{+0.4}_{-1.0})$.