Elemental Abundances and Ages of $z\sim0.7$ Quiescent Galaxies on the Mass-Size Plane: Implication for Chemical Enrichment and Star-Formation Quenching

TL;DR

This study analyzes elemental abundances and ages of quiescent galaxies at redshift ~0.7, revealing how chemical enrichment and galaxy size relate to star formation history and quenching processes.

Contribution

It provides new insights into the relationship between metallicity, size, and age in quiescent galaxies at intermediate redshift, extending low-redshift findings.

Findings

Metallicity correlates with mass-to-size ratio, with more compact galaxies being more metal-rich.

No variation of [Mg/Fe] with mass or size, but older galaxies tend to be more metal-poor.

Mass-[Fe/H] and mass-[Mg/H] relations have increased by ~0.2 dex over 7 Gyr.

Abstract

We present elemental abundances and stellar population ages for 68 massive quiescent galaxies at $0.59\leq z\leq0.75$ from the LEGA-C survey. The abundance patterns and ages, derived from full-spectrum modeling, are examined as a function of stellar mass ($M_*$) and size (i.e., half-light radius; $R_e$). We find that both [Mg/H] and [Fe/H] do not vary with stellar mass but are correlated with $M_*/R_e$ for quiescent galaxies with $M_*>10^{10.5} M_\odot$. Thus, at fixed mass, compact quiescent galaxies are on average more metal rich. This result reinforces the picture that supernova feedback and gravitational potential regulate chemical enrichment. [Mg/Fe] does not vary with $M_*$ or $M_*/R_e$, but there is a marginal positive relation between age and mass. Our results support low-redshift findings that more massive galaxies form their stars at earlier times. However, in contrast to low-redshift studies, star formation timescale does not appear to depend on mass or size. We also compare the mass-[Fe/H] and mass-[Mg/H] relations to stacks of quiescent galaxies at $z\sim0$ and find that both relations increase by $\sim0.2$ dex over the past 7 Gyr. Furthermore, at $z\sim0.7$ we find a clear trend with age, such that older quiescent galaxies have lower metallicities. Both results can be explained by a chemical evolution model in which galaxies quench via gas removal. Future work, in particular with JWST/NIRSpec, will extend this analysis to higher redshifts, allowing us to fully exploit abundance patterns to study the formation histories of quiescent galaxies.