Dynamical analysis of the dark matter and black hole mass in the dwarf spheroidal LEO I*

We take new central kinematic measurements of the Milky Way dwarf spheroidal Leo I, finding a steady rise in the velocity dispersion in the central 300”, suggesting the existence of a black hole. We revisit previously published data on the same central region and identify crowding effects, which lower the prior measured dispersions. Combining our measurements and those of the literature unaffected by crowding, we apply axisymmetric, orbit-based models to measure the stellar mass-to-light ratio, black hole mass and a cored-logarithmic dark halo. We use a few models that include possible tidal effects of the Milky Way, and find in all a consistent value for the mass of the black hole of 3.4±1.5×10⁶ solar masses, with the no black-hole case excluded at high significance (7<Δχ²<13). The dark halo parameters are heavily affected by the tidal models though, with their circular velocities among 10 km/s to 60 km/s. If confirmed, a black hole of this mass, about 10% of the host mass, would a have a significant effect on dwarf galaxy formation and evolution.