Simulations of the Milky Way’s central molecular zone – I. Gas dynamics

Abstract

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. 2011. (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 $1\rm \, M_\odot \, yr^{-1}$, consistent with observational determinations. (4) Supernova feedback can drive an inflow from the CMZ inwards towards the circumnuclear disc of the order of $\sim 0.03\, \rm M_\odot \, yr^{-1}$. (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 ≲ 30 pc) to the Galactic centre, but are also connected to the larger-scale streams at R ≳ 100 pc.

The formation and early evolution of embedded star clusters in spiral galaxies

“…We use two different spiral models, with different strength spiral arms as a means of examining the role of spiral arms. Previous work has found that spiral arms do not typically make a large difference to the global star formation rate in numerical simulations galaxies (Dobbs et al 2011;Pettitt et al 2017;Tress et al 2020;Kim et al 2020), rather the gas is simply gathered together in the spiral arms (Elmegreen & Elmegreen 1986;Vogel et al 1988). Observations of nearby arms in our Galaxy suggest they do not have a significant role (Eden et al 2013(Eden et al , 2015Urquhart et al 2021), however there is some recent observational evidence that spiral arms have some impact on star formation rates over larger galaxy samples (Yu et al 2021).…”

Jeans modelling of the Milky Way’s nuclear stellar disc

“…Thus studying them can give us new insight on the kinetic theory and heating mechanisms of stellar discs. Second, constraining the gravitational potential created by the NSD is crucially important to understand the gas flows in the CMZ and the inward transport of gas from the CMZ down to the central black hole (Tress et al 2020;Li et al 2021). Third, we need to first study equilibrium models if we want to understand the instabilities that might lead to the formation of inner bars (Erwin 2011;Bittner et al 2021).…”

The formation and early evolution of embedded star clusters in spiral galaxies

“…We use two different spiral models, with different strength spiral arms as a means of examining the role of spiral arms. Previous work has found that spiral arms do not typically make a large difference to the global star formation rate in numerical simulations galaxies (Dobbs et al 2011;Pettitt et al 2017;Tress et al 2020;Kim et al 2020), rather the gas is simply gathered together in the spiral arms (Elmegreen & Elmegreen 1986;Vogel et al 1988). Observations of nearby arms in our Galaxy suggest they do not have a significant role (Eden et al 2013(Eden et al , 2015Urquhart et al 2021), however there is some recent observational evidence that spiral arms have some impact on star formation rates over larger galaxy samples (Yu et al 2021).…”