Kavli Affiliate: Huawei Zhang
| First 5 Authors: Gaochao Liu, Yang Huang, Sarah Ann Bird, Huawei Zhang, Fei Wang
| Summary:
Based on a large spectroscopic sample of $sim$ 4,300 RR Lyrae stars with
metallicity, systemic radial velocity and distance measurements, we present a
detailed analysis of the chemical and kinematic properties of the Galactic
halo. Using this sample, the metallicity distribution function (MDF) as a
function of $r$ and the velocity anisotropy parameter $beta$ profiles (for
different metallicity populations) are derived for the stellar halo. Both the
chemical and kinematic results suggest that the Galactic halo is composed of
two distinct parts, the inner halo and outer halo. The cutoff radius ($sim$ 30
kpc) is similar to the previous break radius found in the density distribution
of the stellar halo. We find that the inner part is dominated by a metal-rich
population with extremely radial anisotropy ($beta sim 0.9$). These features
are in accordance with those of “{it Gaia}-Enceladus-Sausage” (GES) and we
attribute this inner halo component as being dominantly composed of stars
deposited from this ancient merged satellite. We find that GES probably has a
slightly negative metallicity gradient. The metal-poor populations in the inner
halo are characterized as a long-tail in MDF with an anisotropy of $beta sim
0.5$, which is similar to that of the outer part. The MDF for the outer halo is
very broad with several weak peaks and the value of $beta$ is around 0.5 for
all metallicities.
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