The Pristine Inner Galaxy Survey (PIGS) I: tracing the kinematics of metal-poor stars in the Galactic bulge. (18th October 2019)

• Record Type: Journal Article
• Authors: Arentsen, A; Starkenburg, E; Martin, N F; Hill, V; Ibata, R; Kunder, A; Schultheis, M; Venn, K A; Zucker, D B; Aguado, D; Carlberg, R; González Hernández, J I; Lardo, C; Longeard, N; Malhan, K; Navarro, J F; Sánchez-Janssen, R; Sestito, F; Thomas, G; Youakim, K; Lewis, G F; Simpson, J D; Wan, Z
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 491:Number 1(2020)
• Page Start: L11
• Page End: L16
• Publication Date: 2019-10-18
• Subjects: Galaxy: bulge -- Galaxy: evolution -- Galaxy: formation -- Galaxy: halo -- Galaxy: kinematics and dynamics -- Galaxy: structure; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/slz156
• Languages: English
• ISSNs: 1745-3933

Abstract

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 ($\rm {[Fe/H]}\, \lt -1.0$ ) 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 $-3.0 \lt \rm {[Fe/H]}\, \lt -0.5$, 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.