Constraints on galactic outflows from the metallicity–stellar mass–SFR relation of EAGLE simulation andSDSSgalaxies

Abstract

ABSTRACTStellar feedback-driven outflows regulate the stellar formation and chemical enrichment of galaxies, yet the underlying dependence of mass outflow rate on galaxy properties remains largely unknown. We develop a simple yet comprehensive non-equilibrium chemical evolution model (NE-CEM) to constrain the mass-loading factor η of outflows using the metallicity-stellar mass–SFR relation observed by Sloan Digital Sky Survey (SDSS) at z = 0. Our NE-CEM predicts the chemical enrichment by explicitly tracking both the histories of star formation and mass-loading. After exploring the eagle simulation, we discover a compact yet flexible model that accurately describes the average star formation histories of galaxies. Applying a novel method of chemically measuring η to eagle, we find η can be parametrized by its dependence on stellar mass and specific SFR as $\log \eta \propto M_*^{\alpha }s{\mathrm{SFR}}^{\beta }$, with α = − 0.12 and β = 0.32 in eagle. Our chemically inferred η agrees remarkably well with the kinematic measurements by Mitchell et al. After extensive tests with eagle, we apply an NE-CEM Bayesian analysis to the SDSS data, yielding a tight constraint of $\log (\eta /0.631) = 0.731{\pm }0.002\times (M_*/10^{9.5}\, \mathrm{M}_{\odot })^{-0.222\pm 0.004} (s{\mathrm{SFR}}/10^{-9.5}\, \mathrm{yr}^{-1})^{0.078\pm 0.003}$, in good agreement with the down-the-barrel measurements. Our best-fitting NE-CEM not only accurately describes the metallicity-stellar mass–SFR relation at z = 0, but also successfully reproduce the so-called ‘fundamental metallicity relation’ at higher redshifts. Our results reveal that different galaxies form stars and enrich their gas in a non-equilibrium but strikingly coherent fashion across cosmic time.