Kinematics of the Tucana Dwarf Galaxy

We measure a systemic velocity for the system of v_Tuc_=216.7^+2.9^_-2.8_km/s, and a velocity dispersion of {sigma}_v,Tuc_=14.4^+2.8^_-2.3_km/s. We also detect a rotation gradient of dv_r_/d{Chi}=7.6^+4.2^_-4.3_km/s/kpc, which reduces the systemic velocity to v_Tuc_=215.2^+2.8^_-2.7_km/s and the velocity dispersion to {sigma}_v,Tuc_=13.3^+2.7^_-2.3_km/s.

We perform Jeans modelling of the density profile of Tucana, using the line-of-sight velocities of the member stars. We find that it favours a high central density consistent with 'pristine' subhaloes in {Lambda} cold dark matter, and a massive dark matter halo (~10^10^M_{sun}_) consistent with expectations from abundance matching. Tucana appears to be significantly more centrally dense than other isolated Local Group dwarfs, making it an ideal laboratory for testing dark matter models.