From Carbon to Cobalt: Chemical Compositions and Ages of z ∼ 0.7 Quiescent Galaxies

• Published in: The Astrophysical journal 2023-05, Vol.948 (2), p.140
• Main Authors: Beverage, Aliza G., Kriek, Mariska, Conroy, Charlie, Sandford, Nathan R., Bezanson, Rachel, Franx, Marijn, van der Wel, Arjen, Weisz, Daniel R.
• Format: Article
• Language: English
• Subjects: Abundance; Astrophysics; Chemical composition; Chemical evolution; Chromium; Cobalt; Dispersion; Early-type galaxies; Galaxies; Galaxy abundances; Galaxy evolution; Galaxy stellar content; Iron; Magnesium; Metallicity; Silicon; Spectroscopy; Star & galaxy formation; Star formation; Stars & galaxies; Stellar age; Stellar evolution; Titanium; Velocity
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/acc176

We present elemental abundance patterns (C, N, Mg, Si, Ca, Ti, V, Cr, Fe, Co, and Ni) for a population of 135 massive quiescent galaxies at z ∼ 0.7 with ultra-deep rest-frame optical spectroscopy drawn from the LEGA-C survey. We derive average ages and elemental abundances in four bins of stellar velocity dispersion ( σ v ) ranging from 150–250 km s −1 using a full-spectrum hierarchical Bayesian model. The resulting elemental abundance measurements are precise to 0.05 dex. The majority of elements, as well as the total metallicity and stellar age, show a positive correlation with σ v . Thus, the highest dispersion galaxies formed the earliest and are the most metal-rich. We find only mild or nonsignificant trends between [X/Fe] and σ v , suggesting that the average star formation timescale does not strongly depend on velocity dispersion. To first order, the abundance patterns of the z ∼ 0.7 quiescent galaxies are strikingly similar to those at z ∼ 0. However, at the lowest-velocity dispersions, the z ∼ 0.7 galaxies have slightly enhanced N, Mg, Ti, and Ni abundance ratios and earlier formation redshifts than their z ∼ 0 counterparts. Thus, while the higher-mass quiescent galaxy population shows little evolution, the low-mass quiescent galaxies population has grown significantly over the past 6 Gyr. Finally, the abundance patterns of both z ∼ 0 and z ∼ 0.7 quiescent galaxies differ considerably from theoretical prediction based on a chemical evolution model, indicating that our understanding of the enrichment histories of these galaxies is still very limited.