Pristine Inner Galaxy Survey PIGS VIII

The azimuthal velocity v_phi_ also decreases between [Fe/H]=-1.0 and -2.0, but is constant for VMP stars (at ~40km/s). The carbon-enhanced metal- poor (CEMP) stars in PIGS appear to have similar orbital properties compared to normal VMP stars. Our results suggest a possible transition between two spheroidal components - a more metal-rich, more concentrated, faster rotating component, and a more metal-poor, more extended and slower/non-rotating component.

We propose that the former may be connected to pre-disc in-situ stars (or those born in large building blocks), whereas the latter may be dominated by contributions from smaller galaxies. This is an exciting era where large metal-poor samples, such as in this work (as well as upcoming surveys, e.g., 4MOST), shed light on the earliest evolution of our Galaxy.