Through thick and thin: Structure of the Galactic thick disc from extragalactic surveys

Abstract

We aim to understand the accretion history of the Milky Way by exploring the vertical and radial properties of the Galactic thick disc. We study the chemical and kinematic properties of roughly a thousand spectra of faint magnitude foreground Galactic stars observed serendipitously during extra-galactic surveys in four lines-of-sight: three in the southern Galactic hemisphere (surveys of the Carina, Fornax and Sculptor dwarf spheroidal galaxies) and one in the northern Galactic hemisphere (a survey of the Sextans dwarf spheroidal galaxy). The foreground stars span distances up to 3kpc from the Galactic plane and Galactocentric radii up to 11kpc. Only three lines-of-sight have a sufficient number of foreground stars for a robust analysis. Towards Sextans in the Northern Galactic hemisphere and Sculptor in the South, we measure a consistent decrease in mean metallicity with height from the Galactic plane, suggesting a chemically symmetric thick disc. This decrease can either be due to an intrinsic thick disc metallicity gradient, or simply due to a change in the thin disc/thick disc population ratio and no intrinsic metallicity gradients for the thick disc. We favour the latter explanation. In contrast, we find evidence of an unpredicted metal-poor population in the direction of Carina. This population was earlier detected by Wyse et al. (2006), but our more detailed analysis provides robust estimates of its location (|Z|<1kpc), metallicity (-2<[M/H]<-1 dex) and azimuthal orbital velocity (V_phi ~120 km/s). Given the chemo-dynamical properties of the over-density towards the Carina line-of-sight, we suggest that it represents the metal-poor tail of the canonical thick disc. In spite of the small number of stars available, we suggest that this metal-weak thick disc follows the often suggested thick disc velocity-metallicity correlation of dV_phi/d[M/H]~40-50km/s/dex.

Accepted in A&A, 17 pages, 18 figures

References in corpus (15)

• The Radial Velocity Experiment (RAVE): first data release
• alpha-, r-, and s-process element trends in the Galactic thin and thick disks
• Outer structure of the Galactic warp and flare: explaining the Canis Major over-density
• The DART imaging and CaT survey of the Fornax Dwarf Spheroidal Galaxy
• The Radial Velocity Experiment (RAVE): second data release
• The Milky Way's Stellar Disk
• Analysis and calibration of CaII triplet spectroscopy of Red Giant Branch stars from VLT/FLAMES observations
• Automated derivation of stellar atmospheric parameters and chemical abundances: the MATISSE algorithm
• Elemental abundances in the atmosphere of clump giants
• The distribution of the ISM in the Milky Way A three-dimensional large-scale model
• Two Disk Components from a Gas Rich Disk-Disk Merger
• The Kinematics of Thick Disks in Nine External Galaxies
• Velocity Shear of the Thick Disk from SPM3 Proper Motions at the South Galactic Pole
• Metallicity Gradients of Thick Disk Dwarf Stars
• Characterisation of the Galactic thin disc with Corot targets

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• The Gaia-ESO Survey: Characterisation of the [alpha/Fe] sequences in the Milky Way discs
• Stellar ages, masses, extinctions and orbital parameters based on spectroscopic parameters of Gaia DR3
• Characterizing the High-Velocity Stars of RAVE: The Discovery of a Metal-Rich Halo Star Born in the Galactic Disk
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