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Dynamical properties of ancient stars in the inner Milky Way with PIGS

Published online by Cambridge University Press:  30 October 2025

A. Arentsen Open the ORCID record for A. Arentsen [Opens in a new window] ,
G. Monari ,
A. Queiroz ,
E. Starkenburg ,
N. F. Martin  and
C. Chiappini
A. Arentsen*
Affiliation:
Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
G. Monari
Affiliation:
Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, F-67000 Strasbourg, France
A. Queiroz
Affiliation:
Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany
E. Starkenburg
Affiliation:
Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV, Groningen, the Netherlands
N. F. Martin
Affiliation:
Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, F-67000 Strasbourg, France Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
C. Chiappini
Affiliation:
Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany
*
email: anke.arentsen@ast.cam.ac.uk
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Abstract

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We present recent results from the Pristine Inner Galaxy Survey (PIGS), which used metallicity-sensitive narrow-band CaHK photometry to identify and follow up spectroscopically thousands of ancient metal-poor candidates in the bulge. For the spectroscopic PIGS sample, we derive distances with StarHorse and compute orbital properties in a realistic potential including a bar. We find that a significant fraction of metal-poor stars is confined to the inner Galaxy (apocentre < 4 kpc), with an estimated confined fraction of 80%/50% at [Fe/H] = − 1.0/ − 2.0. We also find that the very metal-poor population has a net prograde rotation, with a υϕ ∼ 40 kms−1. It is still under discussion what the origin is of the population of very metal-poor inner Galaxy stars – it is likely a combination of in-situ and accreted stars. In future, spectroscopic observations from 4MOST will be crucial to complete our picture.

Keywords

Galaxy: bulgeGalaxy: haloGalaxy: kinematics and dynamicsstars: Population II

Information

Type
Contributed Paper
Information
Proceedings of the International Astronomical Union , Volume 19 , Symposium S379: Dynamical Masses of Local Group Galaxies , December 2023 , pp. 59 - 64
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Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of International Astronomical Union

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