The 3D structure of the Galactic bulge

Abstract

We review the observational evidences concerning the three-dimensional structure of the Galactic bulge. Although the inner few kpc of our Galaxy are normally referred to as {\it the bulge}, all the observations demonstrate that this region is dominated by a bar, i.e., the bulge is a bar. The bar has a boxy/peanut (X\--shaped) structure in its outer regions, while it seems to become less and less elongated in its innermost region. A thinner and longer structure departing from the main bar has also been found, although the observational evidences that support the scenario of two separate structures has been recently challenged. Metal poor stars ([Fe/H]$\lesssim -0.5$ dex) trace a different structure, and also have different kinematics.

12 pages, 5 figures, accepted for publication on PASA

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• The Frequency and Stellar-Mass Dependence of Boxy/Peanut-Shaped Bulges in Barred Galaxies
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• The WFC3 Galactic Bulge Treasury Program: Relative Ages of Bulge Stars of High and Low Metallicity
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• Quantifying the (X/peanut)-shaped Structure of the Milky Way - New Constraints on the Bar Geometry
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• Weighing the two stellar components of the Galactic Bulge
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• Internal kinematics and structure of the bulge globular cluster NGC 6569
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• Blanco DECam Bulge Survey (BDBS) V. Cleaning the foreground populations from Galactic bulge colour-magnitude diagrams using Gaia EDR3
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• The Galactic Bulge exploration IV.: RR~Lyrae stars as traces of the Galactic bar -- 3D and 5D analysis, extinction variation
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