Kavli Affiliate: Andrey Kravtsov
| First 5 Authors: Elliot Y. Davies, Elliot Y. Davies, , ,
| Summary:
The stellar halo of the Milky Way comprises an abundance of chemical
signatures from accretion events and textitin-situ evolution, that form an
interweaving tapestry in kinematic space. To untangle this, we consider the
mixtures of chemical information, in a given region of integral of motion
space, as a variant of the blind source separation problem using non-negative
matrix factorisation (NMF). Specifically, we examine the variation in [Fe/H],
[Mg/Fe], and [Al/Fe] distributions of APOGEE DR17 stars across the $(E,L_z)$
plane of the halo. When 2 components are prescribed, the NMF algorithm splits
stellar halo into low- and high-energy components in the $(E,L_z)$ plane which
approximately correspond to the accreted and textitin-situ halo
respectively. We use these components to define a boundary between the
textitin-situ and the accreted stellar halo, and calculate their fractional
contribution to the stellar halo as a function of energy, galactocentric
spherical radius ($r$), height ($z$), and galactocentric cylindrical radius
($R$). Using a stellar halo defined by kinematic cuts, we derive a boundary in
$(E,L_z)$ space where the halo transitions from textitin-situ dominated to
accretion dominated. Spatially, we find that this transition happens at
$(r,z,R) approx (8.7, 3.0, 8.1)$ kpc. We find that between 34% to 53% of the
stellar halo’s content is of accreted origin. Upon prescribing more components
to the NMF model, we find evidence for overlapping chemical evolution
sequences. We examine features within these components that resemble known
substructures in the halo, such as textitEos and textitAurora.
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