De Re Metallica: The cosmic chemical evolution of galaxies

TL;DR

This review synthesizes how galaxies acquire and distribute heavy elements across cosmic time, tying metallicity to star formation, gas inflows/outflows, and environment. It surveys the methods for measuring stellar and gas-phase abundances, highlighting Te-based, RL, photoionization, and strong-line calibrations, as well as absorption and X-ray techniques. The article then integrates these measurements with galaxy evolution models (analytical, SAMs, and hydrodynamical simulations) and foregrounds key scaling relations such as the MZR and FMR, including their redshift evolution and local (spatially resolved) manifestations. It highlights that while strong progress has been made, significant uncertainties remain in calibrations, ISM physics, and the fate of metals in CGM/IGM, with future facilities like JWST, ELTs, ALMA, and XRISM poised to dramatically advance the field.

Abstract

The evolution of the content of heavy elements in galaxies, the relative chemical abundances, their spatial distribution, and how these scale with various galactic properties, provide unique information on the galactic evolutionary processes across the cosmic epochs. In recent years major progress has been made in constraining the chemical evolution of galaxies and inferring key information relevant to our understanding of the main mechanisms involved in galaxy evolution. In this review we provide an overview of these various areas. After an overview of the methods used to constrain the chemical enrichment in galaxies and their environment, we discuss the observed scaling relations between metallicity and galaxy properties, the observed relative chemical abundances, how the chemical elements are distributed within galaxies, and how these properties evolve across the cosmic epochs. We discuss how the various observational findings compare with the predictions from theoretical models and numerical cosmological simulations. Finally, we briefly discuss the open problems the prospects for progress in this field in the nearby future.

Figures (60)

• Figure 1: Timescales of production of various elements after a single episode of star formation (a single stellar population, SSP) of solar metallicity, based on the model by Vincenzo et al. (in prep.), see text for details. The upper panel shows the production rate in M$_\odot$/Gyr normalized to 1 M$_\odot$ of formed stars. The lower panel shows the cumulative mass produced, normalized to the amount after one Hubble time. Oxygen (red line) in mainly produced by CC SNe and therefore has the shortest formation timescales. Iron (blue line) is dominated by type Ia SNe, Carbon (black) has contributions from both kinds of SNe and from AGB stars. The production of Nitrogen (green) is dominated by AGB stars. In this plot, the production of elements before 30Myr is due to CC SNe, type Ia SNe are described by a power-law $t^{-1}$ after 40Myr and up to the Hubble time, and AGB stars give additional contributions above this power-law at intermediate ages of $\sim$0.04-5 Gyr.
• Figure 2: The wavelength ranges covered by the set of Lick indices (grey rectangles) used by Onodera15 are overplotted on a stacked spectrum of a sample of quenched galaxies at $z\sim1.6$. The red line is the stacked spectrum, with orange lines showing the $\pm1\sigma$ uncertainties. The green line is the best-fitting model stellar spectrum.
• Figure 3: Stacked rest-frame UV spectrum of star-forming galaxies at $\langle z \rangle \sim2.4$, from Steidel16. The most important absorption and emission features are shown, color-coded according to their nature: red, stellar absorption features; green, interstellar absorption features; blue, nebular emission lines; violet, fine structure lines.
• Figure 4: The radial metallicity gradient in M300 measured by three different methods: blue supergiants (BSG, blue triangles), red supergiants (RSG, red dots), HII region metallicities with the "$T_e$" method (green squares). The agreement is remarkable. From Davies15.
• Figure 5: Difference between stellar and gaseous metallicity as inferred "directly" from the $T_e$ method (blue circles) and from the Recombination Lines (orange squares) in a sample of local galaxies and star-forming regions, as a function of stellar metallicity. The vertical line shows the adopted Solar value. From Bresolin16.