Dynamical evidence for a strong tidal interaction between the Milky Way and its satellite, Leo V

We present a chemodynamical analysis of the Leo~V dwarf galaxy, based on Keck II DEIMOS spectra of 8 member stars. We find a systemic velocity for the system of $⟨v_r⟩=170.9_{-1.9}^{+2.1}$kms${}^{-1}$, and barely resolve a velocity dispersion for the system, with $\sigma_{vr} = 2.3^{+3.2}{-1.6}$kms$^{-1}$, consistent with previous studies of Leo~V. The poorly resolved dispersion means we are unable to adequately constrain the dark matter content of Leo~V. We find an average metallicity for the dwarf of [Fe/H]$=-2.48\pm 0.21$, and measure a significant spread in the iron abundance of its member stars, with $-3.1\le$[Fe/H]$\le -1.9$ dex, which cleanly identifies Leo~V as a dwarf galaxy that has been able to self-enrich its stellar population through extended star formation. Owing to the tentative photometric evidence for tidal substructure around Leo~V, we also investigate whether there is any evidence for tidal stripping or shocking of the system within its dynamics. We measure a significant velocity gradient across the system, of $\frac{\mathrm{d}v}{\mathrm{d}\chi }=-4.1_{-2.6}^{+2.8}$kms${}^{-1}$ per arcmin (or $\frac{{\rm d}v}{{\rm d}\chi} = -71.9^{+50.8}{-45.6}$kms$^{-1}$kpc$^{-1}$), which points almost directly toward the Galactic centre. We argue that Leo~V is likely a dwarf on the brink of dissolution, having just barely survived a past encounter with the centre of the Milky Way.