Unveiling the Galactic Baryon Cycle Process by an Empirical Model

We propose an empirical model to describe and constrain the baryon cycle process during galaxy evolution. This model utilizes the evolution of star formation rate, derived from the stellar mass–halo mass relations across different redshifts, and the cold gas content, derived from the NeutralUniverseMachine model, to constrain gas accretion and recycle of gas outflow in the model galaxy. Additionally, through detailed modeling of each cycle process, particularly the recycling process, and utilizing the gas-phase mass–metallicity relation at z = 0 as a constraint, our model establishes a relation between the recycle fraction and halo mass. It is found that the fraction of gas recycled from the outflow is a function of halo mass, with a value of 25% in galaxies with a halo mass of ∼10 10.4 M ⊙ , increasing to 75% in halos with a mass of ∼10 12 M ⊙ . We also find that the mass loading factor from the FIRE-2 simulation matches well with the constraints from both observational data and our model. Furthermore, using the gas content and metallicity of the circumgalactic medium (CGM) obtained from hydrodynamical simulations as constraints, our model predicts that, on average, 70% of universal baryon accretion is accreted to the halo and 80% of the nonrecycled gas in the outflow has escaped from the galaxy, entering the intergalactic medium (IGM). However, we note that future observational data are needed to finally constrain the mass and metal exchange between the CGM and the IGM.