Understanding the baryon cycle: Fueling star formation via inflows in Milky Way-like galaxies

¹ Department of Physics and Astronomy “Augusto Righi”, University of Bologna, Via P. Gobetti 93/2, I-40129 Bologna, Italy
² INAF, Astrophysics and Space Science Observatory Bologna, Via P. Gobetti 93/3, I-40129 Bologna, Italy
³ Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁴ Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
⁵ Department of Astronomy, Tsinghua University, Beijing 100084, China
⁶ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁷ The NSF AI Institute for Artificial Intelligence and Fundamental Interactions, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

^⋆ Corresponding author; filippo.barbani2@unibo.it

Received: 14 October 2024
Accepted: 31 March 2025

Abstract

Context. Galaxies are not isolated systems, as they interact with their surroundings throughout their lifetimes by both ejecting gas via stellar feedback and accreting gas from their environment. Understanding the interplay between the gas ejected from the disc and the circumgalactic medium (CGM) is crucial to learning how star-forming galaxies evolve.

Aims. Our goal is to understand how gas in the CGM is accreted onto the inner regions of the star-forming disc, making it available for the formation of new stars. Specifically, we explore the connection between stellar feedback and gas accretion from the CGM in Milky Way-like galaxies, aiming to unveil the complex mechanisms driving the evolution of star-forming galaxies. We focus on the distribution of vertical and radial gas flows to and from the disc as a function of galactocentric radius and examine the implications of these processes for the evolution of such galaxies.

Methods. We used the moving-mesh code AREPO coupled with the SMUGGLE sub-grid model to perform hydrodynamic N-body simulations of nine different galaxies surrounded by a hot (T ∼ 10⁶ K) CGM (also called galactic corona). Each simulation has a different structure of the gaseous disc in terms of mass and scale length, which allows us to study how the dynamics of the gas can be affected by disc structure.

Results. We find evidence of a crucial link between stellar feedback processes and gas accretion from the CGM, which collectively play an essential role in sustaining ongoing star formation in the disc. In particular, the ejection of gas from the plane of the disc by stellar feedback leads to the generation of a baryon cycle where the CGM gas is preferentially accreted onto the external regions of the disc (≈3 − 10 M_⊙ yr⁻¹ of gas is accreted into the entire disc). From these regions, it is then transported to the centre with radial mass rates of ≈1 − 4 M_⊙ yr⁻¹ on average, owing to angular momentum conservation. It then leads to the formation of new stars and restarts the whole cycle. We find that both vertical accretion onto the inner regions of the disc and the radial transport of gas from the disc outskirts are necessary to sustain star formation.