Kavli Affiliate: Andrey Kravtsov
| First 5 Authors: Evgeny P. Kurbatov, Vasily Belokurov, Sergey Koposov, Andrey Kravtsov, Elliot Y. Davies
| Summary:
The innermost portions of the Milky Way’s stellar halo have avoided scrutiny
until recently. The lack of wide-area survey data, made it difficult to
reconstruct an uninterrupted view of the density distribution of the metal-poor
stars inside the Solar radius. In this study, we utilize red giant branch (RGB)
stars from Gaia, with metallicities estimated using spectro-photometry from
Gaia Data Release 3. Accounting for Gaia’s selection function, we examine the
spatial distribution of metal-poor ([M/H]<-1.3) RGB stars, from the Galactic
centre (r~1 kpc) out to beyond the Solar radius (r~18 kpc). Our best-fitting
single-component cored power-law model shows a vertical flattening of ~0.5 and
a slope -3.4, consistent with previous studies. Motivated by the mounting
evidence for two distinct stellar populations in the inner halo, we
additionally test a range of two-component models. One of the components models
the tidal debris from the Gaia Sausage/Enceladus merger, while the other
captures the Aurora population — stars that predate the Galactic disk
formation. Our best-fit two-component model suggests that both populations
contribute equally around the Solar radius, but Aurora dominates the inner halo
with a steeper power-law index of -4.5, in agreement with the nitrogen-rich
star distribution measured by Horta et al. (2021).
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