The Stellar Metallicities of Massive Quiescent Galaxies at 1.0 < z < 1.3 from KMOS + VANDELS

• Published in: The Astrophysical journal 2022-04, Vol.929 (2), p.131
• Main Authors: Carnall, Adam C., McLure, Ross J., Dunlop, James S., Hamadouche, Massissilia, Cullen, Fergus, McLeod, Derek J., Begley, Ryan, Amorin, Ricardo, Bolzonella, Micol, Castellano, Marco, Cimatti, Andrea, Fontanot, Fabio, Gargiulo, Adriana, Garilli, Bianca, Mannucci, Filippo, Pentericci, Laura, Talia, Margherita, Zamorani, Giovani, Calabro, Antonello, Cresci, Giovanni, Hathi, Nimish P.
• Format: Article
• Language: English
• Subjects: Abundance; Astronomical models; Astrophysics; Chemical abundances; Downsizing; Evolution; Galaxies; Galaxy spectroscopy; High-redshift galaxies; Iron; James Webb Space Telescope; Local group (astronomy); Magnesium; Measuring instruments; Metallicity; Quenched galaxies; Red shift; Space telescopes; Star & galaxy formation; Star formation; Stars & galaxies; Stellar age; Stellar evolution; Stellar mass; Universe
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac5b62

We present a rest-frame UV–optical ( λ = 2500–6400 Å) stacked spectrum representative of massive quiescent galaxies at 1.0 < z < 1.3 with log( M * / M ⊙ ) > 10.8. The stack is constructed using VANDELS survey data, combined with new KMOS observations. We apply two independent full-spectral-fitting approaches, measuring a total metallicity [Z/H] = −0.13 ± 0.08 with Bagpipes and [Z/H] = 0.04 ± 0.14 with Alf , a fall of ∼0.2–0.3 dex compared with the local universe. We also measure an iron abundance [Fe/H] = −0.18 ± 0.08, a fall of ∼0.15 dex compared with the local universe. We measure the alpha enhancement via the magnesium abundance, obtaining [Mg/Fe] = 0.23 ± 0.12, consistent with galaxies of similar mass in the local universe, indicating no evolution in the average alpha enhancement of log( M * / M ⊙ ) ∼ 11 quiescent galaxies over the last ∼8 Gyr. This suggests the very high alpha enhancements recently reported for several bright z ∼ 1–2 quiescent galaxies are due to their extreme masses, log( M * / M ⊙ ) ≳ 11.5, in accordance with the well-known downsizing trend, rather than being typical of the z ≳ 1 population. The metallicity evolution we observe with redshift (falling [Z/H], [Fe/H], constant [Mg/Fe]) is consistent with recent studies. We recover a mean stellar age of 2.5 − 0.4 + 0.6 Gyr, corresponding to a formation redshift z form = 2.4 − 0.3 + 0.6 . Recent studies have obtained varying average formation redshifts for z ≳ 1 massive quiescent galaxies, and, as these studies report consistent metallicities, we identify models with different star formation histories as the most likely cause. Larger spectroscopic samples from upcoming ground-based instruments will provide precise constraints on ages and metallicities at z ≳ 1. Combining these with precise stellar mass functions for z > 2 quiescent galaxies from the James Webb Space Telescope will provide an independent test of formation redshifts derived from spectral fitting.