Abstract
Analytical models of chemical evolution, including inflow and outflow of gas, are important tools to study how the metal content in galaxies evolves as a function of time. In this work, we present new analytical solutions for the evolution of the gas mass, total mass and metallicity of a galactic system, when a decaying exponential infall rate of gas and galactic winds are assumed. We apply our model to characterize a sample of local star-forming and passive galaxies from the Sloan Digital Sky Survey data, with the aim of reproducing their observed mass-metallicity relation; in this way, we can derive how the two populations of star-forming and passive galaxies differ in their particular distribution of ages, formation time scales, infall masses and mass loading factors. We find that the local passive galaxies are on average older and assembled on shorter typical time-scales than the local star-forming ones; on the other hand, the larger mass star-forming galaxies show generally older ages and longer typical formation time-scales compared with the smaller mass star-forming galaxies. Finally, we conclude that the local star-forming galaxies experience stronger galactic winds than the passive galaxy population. We explore the effect of assuming different initial mass functions in our model, showing that to reproduce the observed mass-metallicity relation stronger winds are requested if the initial mass function is top-heavy. Finally, our analytical models predict the assumed sample of local galaxies to lie on a tight surface in the 3D space defined by stellar metallicity, star formation rate and stellar mass, thus mimicking the well-known "fundamental relation".
Highlights
Chemical evolution of galaxies studies how subsequent stellar generations and gas flows alter the chemical composition of the galaxy interstellar medium (ISM) to give rise to the presentday observed chemical abundance pattern of galaxies
We here present the results of an analytical chemical evolution model in which a decaying exponential infall rate of gas is assumed as a function of time; we show that analytical solutions for the evolution of the galaxy metallicity, gas mass, and total mass can be found under this assumption
We remark on the fact that we selected the best chemical evolution models characterizing the Sloan Digital Sky Survey (SDSS) sample of Peng et al (2015) by imposing the set of constraints presented in the previous Sect. 4.3 and by varying all the free parameters simultaneously
Summary
Chemical evolution of galaxies studies how subsequent stellar generations and gas flows alter the chemical composition of the galaxy interstellar medium (ISM) to give rise to the presentday observed chemical abundance pattern of galaxies In this respect, the galaxy star formation and gas mass assembly histories play a major role, together with the assumed initial mass function (IMF) and stellar nucleosynthetic yields. A further fundamental hypothesis is to retain the instantaneous recycling approximation (IRA): all the stars with mass m ≥ 1 M instantaneously die as they form, whereas all the stars with m < 1 M have infinite lifetimes This type of models still represents a useful tool for tracing the metallicity evolution of galaxies, but only when the abundance of chemical elements produced on typical short timescales is considered. Pioneering works in this field are considered those of Schmidt (1963); Searle & Sargent (1972); Tinsley (1974); and Pagel & Patchett (1975)
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