Understanding the Baryon Cycle: Fueling Star Formation via Inflows in Milky Way-like Galaxies

Abstract

Galaxies are not isolated systems; they continuously interact with their surroundings by ejecting gas via stellar feedback and accreting gas from the environment. Understanding the interplay between outflows from the disc and the surrounding circumgalactic medium (CGM) is key to learning how star-forming galaxies evolve. Our goal is to understand how gas in the CGM is accreted onto the inner regions of the disc, making it available for the formation of stars, exploring the connection between stellar feedback and gas accretion from the CGM in Milky Way-like 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. We use the Arepo code coupled with the SMUGGLE sub-grid model to perform hydrodynamic N-body simulations of 9 different galaxies surrounded by a hot CGM. Each simulation features a gaseous disc with different mass and scale length, allowing us to examine how disc structure impacts gas dynamics. We find evidence of a crucial link between stellar feedback and gas accretion from the CGM, which together play an essential role in sustaining ongoing star formation in the disc. In particular, the ejection of gas from the disc plane by stellar feedback leads to the generation of a baryon cycle in which the CGM gas is mainly accreted onto the external regions of the disc ($ \approx 3-10$ M$_{\odot}$ yr$^{-1}$ of gas is accreted into the whole disc). From these regions it is then transported to the centre with radial mass rates $\approx 1-4$ M$_{\odot}$ yr$^{-1}$ on average, owing to angular momentum conservation, forming new stars and starting the whole cycle again. 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.