We use hydrodynamical simulations to study the Milky Way ’ s central molecular zone ( CMZ ) , i.e .
the star-forming nuclear ring at Galactocentric radii R \lesssim 200 pc .
The simulations comprise the gas flow in a Milky Way barred potential out to R = 5 kpc , which is necessary in order to capture the large-scale environment in which the CMZ is embedded and with which it is strongly interacting through the bar-driven inflow .
The simulations also include a non-equilibrium time-dependent chemical network , gas self-gravity , and a sub-grid model for star formation and supernova feedback , all while reaching sub-parsec resolution in the densest regions .
Our main findings are as follows : ( 1 ) The distinction between inner ( R \lesssim 120 pc ) and outer ( 120 \lesssim R \lesssim 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 \simeq 200 pc which is interacting directly 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 \infty -shaped structure identified in Herschel data by Molinari et al .
2011 .
( 3 ) The bar in our simulation efficiently drives an inflow from the Galactic disc ( R \simeq 3 kpc ) down to the CMZ ( R \simeq 200 pc ) of the order of 1 M _ { \odot } yr ^ { -1 } , consistent with observational determinations .
( 4 ) Self-gravity and supernovae feedback can drive an inflow from the CMZ inwards towards the circumnuclear disc of the order of \sim 0.03 M _ { \odot } 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 \lesssim 30 pc ) to the Galactic centre , but are also connected to the larger-scale streams at R \gtrsim 100 pc .