Letter to the Editor

The G-dwarf distribution in star-forming galaxies: A tug of war between infall and outflow

¹ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
e-mail: spitoni@phys.au.dk
² INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy

Received: 19 March 2021
Accepted: 6 April 2021

Abstract

In the past, the cumulative metallicity distribution function (CMDF) turned out to be a useful tool to constrain the accretion history of various components of the Milky Way. In this Letter, by means of analytical, leaky-box chemical evolution models (i.e. including both infall and galactic outflows), we study the CMDF of local star-forming galaxies that follow two fundamental empirical scaling relations, namely the mass-metallicity and main sequence relations. Our analysis shows that galactic winds, which are dominant mostly in low-mass systems, play a fundamental role in shaping this function and, in particular, in determining its steepness and curvature. We show that the CMDF of low-mass (M_⋆/M_⊙ ≤ 10^9.5) and high-mass (M_⋆/M_⊙ >  10^10.5) galaxies substantially deviate from the results of a ‘closed-box’ model, as the evolution of the former (latter) systems is mostly dominated by outflows (infall). In the context of galactic downsizing, we show that downward-concave CMDFs (associated with systems with extremely small infall timescales and with very strong winds) are more frequent in low-mass galaxies, which include larger fractions of young systems and present more substantial deviations from equilibrium between gas accretion and reprocessing (either via star formation or winds).