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arXiv · 1910.06337

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

Anke Arentsen·Else Starkenburg·Nicolas F. Martin·Vanessa Hill·Rodrigo Ibata·Andrea Kunder·Mathias Schultheis·Kim A. Venn·Daniel B. Zucker·David Aguado·Ray Carlberg·Jonay I. González Hernández·Carmela Lardo·Nicolas Longeard·Khyati Malhan·Julio F. Navarro·Ruben Sánchez-Janssen·Federico Sestito·Guillaume Thomas·Kris Youakim·Geraint F. Lewis·Jeffrey D. Simpson·Zhen Wan
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Abstract

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 $\pm$ 4 km$\,$s$^{-1}\,$dex$^{-1}$. These observations may signal a transition between Galactic components of different metallicities and kinematics, a different mapping onto the boxy/peanut-shaped bulge for former disk 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.

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Anke Arentsen, Else Starkenburg, Nicolas F. Martin, Vanessa Hill, Rodrigo Ibata, Andrea Kunder, Mathias Schultheis, Kim A. Venn, Daniel B. Zucker, David Aguado, Ray Carlberg, Jonay I. González Hernández, Carmela Lardo, Nicolas Longeard, Khyati Malhan, Julio F. Navarro, Ruben Sánchez-Janssen, Federico Sestito, Guillaume Thomas, Kris Youakim, Geraint F. Lewis, Jeffrey D. Simpson, Zhen Wan. 2019-10-14. The Pristine Inner Galaxy Survey (PIGS) I: Tracing the kinematics of metal-poor stars in the Galactic bulge. https://doi.org/10.1093/mnrasl/slz156

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