# Kinematics of the Tucana Dwarf Galaxy: An Unusually Dense Dwarf in the Local Group

## TL;DR

This study provides detailed kinematic measurements of the Tucana dwarf galaxy, revealing it as unusually dense and dark matter-rich, offering a unique case for testing dark matter theories.

## Contribution

The paper presents new spectroscopic data and Jeans modeling that show Tucana's high central density and dark matter halo, highlighting its uniqueness among isolated Local Group dwarfs.

## Key findings

- Tucana has a systemic velocity of ~217 km/s.
- Velocity dispersion is about 14.4 km/s, reduced when accounting for rotation.
- Tucana's density profile favors high central density consistent with ΛCDM predictions.

## 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 $v_{\mathrm{Tuc}}=216.7_{-2.8}^{+2.9}$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.