The origin and evolution of the galaxy mass–metallicity relation

Abstract

We use high-resolution cosmological zoom-in simulations from the Feedback in Realistic Environment (FIRE) project to study the galaxy mass-metallicity relations (MZR) from z = 0-6. These simulations include explicit models of the multi-phase ISM, star formation, and stellar feedback. The simulations cover halo masses M halo = 10 9 -10 13 M and stellar masses M * = 10 4 -10 11 M at z = 0 and have been shown to produce many observed galaxy properties from z = 0-6. For the first time, our simulations agree reasonably well with the observed mass-metallicity relations at z = 0-3 for a broad range of galaxy masses. We predict the evolution of the MZR from z = 0-6, as log( 04, for gas-phase and stellar metallicity, respectively. Our simulations suggest that the evolution of MZR is associated with the evolution of stellar/gas mass fractions at different redshifts, indicating the existence of a universal metallicity relation between stellar mass, gas mass, and metallicities. In our simulations, galaxies above M * = 10 6 M are able to retain a large fraction of their metals inside the halo, because metal-rich winds fail to escape completely and are recycled into the galaxy. This resolves a long-standing discrepancy between "sub-grid" wind models (and semi-analytic models) and observations, where common sub-grid models cannot simultaneously reproduce the MZR and the stellar mass functions.

Metal flows of the circumgalactic medium, and the metal budget in galactic haloes

“…Similar representations of the metal flux of m10 and m11 have been previously shown in Ma et al (2016). We demonstrated in M15 that this method of computing fluxes is generally consistent with an alternative method in which particles are tracked directly as they cross spherical interfaces in the CGM.…”

“…We first note that the FIRE simulations reproduce both stellar and gas-phase MZRs (Ma et al 2016), which the semi-analytical works discussed here are tuned to. In Lu et al (2015), metal abundances are used to constrain the maximum value of η for galactic winds in halos of various masses.…”

“…However, the metallicity of the ISM grows between z = 2 and z = 0 by a factor of ∼5, while more than half of all stellar metals are locked into stars at z < 0.5. This significant low-redshift metallicity evolution is key to the success of the FIRE halos matching observed MZR at multiple epochs (Ma et al 2016). The metal content of galaxies in this mass range has been consistently difficult to reproduce in large-volume simulations where winds are prescribed a-priori.…”

“…Many works have yielded insights on how the MZR arises (e.g. Brooks et al 2007;Finlator & Davé 2008;Davé et al 2011;Peeples & Somerville 2013;Torrey et al 2014;Ma et al 2016).…”

“…We will especially focus on the CGM to complement Ma et al (2016), which focused on the metallicity of stars and the ISM. We begin by testing whether the winds transport a large amount of metals to the CGM.…”