Mapping the Outer Halo: New Insights from the Pristine Survey
Recent research from the Pristine Survey has provided new insights into the outer halo of the Milky Way galaxy, focusing on the mapping of red giant stars. The study, titled "The Pristine Survey -- XXVII. Journey to the Galactic outskirts -- Mapping the outer halo red giant stars down to the very metal-poor end," was authored by Akshara Viswanathan and 16 collaborators. It utilizes publicly available data from the Pristine survey to analyze the metallicity distribution of red giant stars in the outer halo, particularly those that are very metal-poor, with metallicity values below -2.5.
The researchers employed two catalogues: the Pristine data release 1 (PDR1) and the Pristine-Gaia synthetic (PGS) catalogues. They developed a selection pipeline to identify red giant branch (RGB) stars based on their brightness and the absence of well-measured parallax data. The study found that the photometric distances derived from these catalogues showed typical uncertainties of 12% and a scatter of up to 20% and 40%, respectively.
One significant outcome of the research is the publication of two RGB catalogues that provide a low-to-no bias view of the metallicity structure versus distance, extending out to approximately 100 kiloparsecs. This data is crucial for understanding the history of the Milky Way's formation and the accretion of dwarf galaxy debris, as it maps the metallicity view of the integrals-of-motion space where such debris retains its orbital parameters over time.
Additionally, the study tentatively associates 41 stars with the stellar counterpart of the Magellanic stream, extending out to 70 kiloparsecs. These findings contribute to the broader understanding of galactic archaeology and the evolution of the Milky Way.
For further details, the paper can be cited as: Viswanathan, A., et al. (2024). The Pristine Survey -- XXVII. Journey to the Galactic outskirts -- Mapping the outer halo red giant stars down to the very metal-poor end. arXiv:2408.17250.