| Abstract | We present new FLAMES+GIRAFFE spectroscopy of 36 member stars in the isolated Local Group dwarf spheroidal galaxy Tucana. We measure a systemic velocity for the system of vTuc=216.7⁺².⁹−₂.₈ km s⁻¹, and a velocity dispersion of σv,Tuc=14.4⁺².⁸−₂.₃ km s−¹. We also detect a rotation gradient of dvᵣ/dχ=7.6⁺⁴.²−₄.₃ km s−¹ kpc−¹, which reduces the systemic velocity to vTuc=215.2⁺².⁸−₂.₇ km s−¹ and the velocity dispersion to σv,Tuc=13.3⁺².⁷−₂.₃ km s−¹. 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 Λ cold dark matter, and a massive dark matter halo (∼10¹⁰ M⊙) 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. |
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