2020MNRAS.499.4455T

We use hydrodynamical simulations to study the Milky Way's central molecular zone (CMZ). The simulations include a non-equilibrium chemical network, the gas self-gravity, star formation, and supernova feedback. We resolve the structure of the interstellar medium at sub-parsec resolution while also capturing the interaction between the CMZ and the bar-driven large-scale flow out to R∼5 kpc. Our main findings are as follows: (1) The distinction between inner (R <= 120 pc) and outer (120 <= R <= 450 pc) CMZ that is sometimes proposed in the literature is unnecessary. Instead, the CMZ is best described as single structure, namely a star-forming ring with outer radius R ≃ 200 pc which includes the 1.3° complex and which is directly interacting with the dust lanes that mediate the bar-driven inflow. (2) This accretion can induce a significant tilt of the CMZ out of the plane. A tilted CMZ might provide an alternative explanation to the ∞-shaped structure identified in Herschel data by Molinari et al. (3) The bar in our simulation efficiently drives an inflow from the Galactic disc (R ≃ 3 kpc) down to the CMZ (R ≃ 200 pc) of the order of 1 M_☉yr^–1, consistent with observational determinations. (4) Supernova feedback can drive an inflow from the CMZ inwards towards the circumnuclear disc of the order of ∼0.03 M_☉yr^–1. (5) We give a new interpretation for the 3D placement of the 20 and 50 km s^–1 clouds, according to which they are close (R <= 30 pc) to the Galactic Centre, but are also connected to the larger scale streams at R >= 100 pc.