A Framework for Empirical Galaxy Phenomenology: The Scatter in Galaxy Ages and Stellar Metallicities

Abstract

We develop a theoretical framework that extracts a deeper understanding of galaxy formation from empirically-derived relations among galaxy properties by extending the main-sequence integration method for computing galaxy star formation histories. We properly account for scatter in the stellar mass-star formation rate relation and the evolving fraction of passive systems and find that the latter effect is almost solely responsible for the age distributions among $z\sim 0$ galaxies with stellar masses above $\sim 10^{10}{\mathrm{M}}_{\odot }$. However, while we qualitatively agree with the observed median stellar metallicity as a function of stellar mass, we attribute our inability to reproduce the distribution in detail largely to a combination of imperfect gas-phase metallicity and $\alpha$/Fe ratio calibrations. Our formalism will benefit from new observational constraints and, in turn, improve interpretations of future data by providing self-consistent star formation histories for population synthesis modeling.

20 pages, 6 figures, 1 table, MNRAS in press, supplementary tables available online

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• Stochastic modelling of star-formation histories II: star-formation variability from molecular clouds and gas inflow
• Stochastic modeling of star-formation histories I: the scatter of the star-forming main sequence
• Evolution of the atomic and molecular gas content of galaxies in dark matter haloes
• Decoding the Star-Forming Main Sequence or: How I Learned to Stop Worrying and Love the Central Limit Theorem
• Star formation quenching imprinted on the internal structure of naked red nuggets
• A single galaxy population? statistical evidence that the Star-Forming Main Sequence might be the tip of the iceberg
• COSMOS Brightest Group Galaxies -- III: Evolution of stellar ages
• MIGHTEE-HI: The star-forming properties of HI selected galaxies