The Pristine Inner Galaxy Survey (PIGS) I: tracing the kinematics of metal-poor stars in the Galactic bulge

A. Arentsen*, E. Starkenburg, N. F. Martin, V. Hill, R. Ibata, A. Kunder, M. Schultheis, K. A. Venn, D. B. Zucker, D. Aguado, R. Carlberg, J. I. González Hernández, C. Lardo, N. Longeard, K. Malhan, J. F. Navarro, R. Sánchez-Janssen, F. Sestito, G. Thomas, K. YouakimG. F. Lewis, J. D. Simpson, Z. Wan

*Corresponding author for this work

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    Our Galaxy is known to contain a central boxy/peanut-shaped bulge, yet the importance of a classical, pressure-supported component within the central part of the Milky Way is still being debated. It should be most visible at low metallicity, a regime that has not yet been studied in detail. Using metallicity-sensitive narrow-band photometry, the Pristine Inner Galaxy Survey (PIGS) has collected a large sample of metal-poor ([Fe/H]<-1.0) stars in the inner Galaxy to address this open question. We use PIGS to trace the metal-poor inner Galaxy kinematics as function of metallicity for the first time. We find that the rotational signal decreases with decreasing [Fe/H], until it becomes negligible for the most metal-poor stars. Additionally, the velocity dispersion increases with decreasing metallicity for -3.0<[Fe/H]<-0.5, with a gradient of-44 ± 4 km s-1 dex-1. These observations may signal a transition between Galactic components of different metallicities and kinematics, a different mapping on to the boxy/peanut-shaped bulge for former disc stars of different metallicities and/or the secular dynamical and gravitational influence of the bar on the pressure-supported component. Our results provide strong constraints on models that attempt to explain the properties of the inner Galaxy.

    Original languageEnglish
    Pages (from-to)L11-L16
    Number of pages6
    JournalMonthly Notices of the Royal Astronomical Society: Letters
    Issue number1
    Publication statusPublished - Jan 2020

    Bibliographical note

    This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society: Letters, Volume 491, Issue 1, January 2020, Pages L11–L16, Copyright 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


    • Galaxy: bulge
    • Galaxy: evolution
    • Galaxy: formation
    • Galaxy: halo
    • Galaxy: kinematics and dynamics
    • Galaxy: structure


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