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 v _ { \mathrm { Tuc } } = 216.7 _ { -2.8 } ^ { +2.9 } kms ^ { -1 } , and a velocity dispersion of \sigma _ { \mathrm { v,Tuc } } = 14.4 _ { -2.3 } ^ { +2.8 } kms ^ { -1 } .
We also detect a rotation gradient of \frac { dv _ { r } } { d \chi } = 7.6 ^ { +4.2 } _ { -4.3 } kms ^ { -1 } kpc ^ { -1 } , which reduces the systemic velocity to v _ { \mathrm { Tuc } } = 215.2 _ { -2.7 } ^ { +2.8 } kms ^ { -1 } and the velocity dispersion to \sigma _ { v, \mathrm { Tuc } } = 13.3 _ { -2.3 } ^ { +2.7 } kms ^ { -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 ’ subhalos in \Lambda CDM , and a massive dark matter halo ( \sim 10 ^ { 10 } M _ { \odot } ) 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 .