Galaxy halo Extremely Metal-Poor stars

Exploiting the action map, we identify 16 and 40 stars dynamically consistent with the Gaia Sausage and Gaia Sequoia accretion events, respectively. The most metal poor of these candidates have metallicities of [Fe/H]=-3.31 and -3.74, respectively, helping to define the low-metallicity tail of the progenitors involved in the accretion events.

We also find, consistent with other studies, that ~21 per cent of the sample have orbits that remain confined to within 3kpc of the Galactic plane, that is, |Z_max_|<=3kpc. Of particular interest is a subsample (~11 per cent of the total) of low |Z_max_| stars with low eccentricities and prograde motions. The lowest metallicity of these stars has [Fe/H]=-4.30 and the subsample is best interpreted as the very low-metallicity tail of the metal-weak thick disc population.