Stellar Metallicities and Elemental Abundance Ratios of z ∼ 1.4 Massive Quiescent Galaxies*

Abstract

The chemical composition of galaxies has been measured out to z ∼ 4. However, nearly all studies beyond z ∼ 0.7 are based on strong-line emission from HII regions within star-forming galaxies. Measuring the chemical composition of distant quiescent galaxies is extremely challenging, as the required stellar absorption features are faint and shifted to near-infrared wavelengths. Here, we present ultra-deep rest-frame optical spectra of five massive quiescent galaxies at z ∼ 1.4, all of which show numerous stellar absorption lines. We derive the abundance ratios [Mg/Fe] and [Fe/H] for three out of five galaxies; the remaining two galaxies have too young luminosity-weighted ages to yield robust measurements. Similar to lower-redshift findings, [Mg/Fe] appears positively correlated with stellar mass, while [Fe/H] is approximately constant with mass. These results may imply that the stellar mass-metallicity relation was already in place at z ∼ 1.4. While the [Mg/Fe]-mass relation at z ∼ 1.4 is consistent with the z < 0.7 relation, [Fe/H] at z ∼ 1.4 is ∼ 0.2 dex lower than at z < 0.7. With a [Mg/Fe] of 0.44 +0.08 −0.07 the most massive galaxy may be more α-enhanced than similar-mass galaxies at lower redshift, but the offset is less significant than the [Mg/Fe] of 0.6 previously found for a massive galaxy at z = 2.1. Nonetheless, these results combined may suggest that [Mg/Fe] in the most massive galaxies decreases over time, possibly by accreting low-mass, less α-enhanced galaxies. A larger galaxy sample is needed to confirm this scenario. Finally, the abundance ratios indicate short star-formation timescales of 0.2 − 1.0 Gyr.

The GOGREEN survey: post-infall environmental quenching fails to predict the observed age difference between quiescent field and cluster galaxies at z &gt; 1

“…This comparison shows that for our sample, UVJ colours are broadly consistent with both D n (4000) and EW([O ii] ) tracers for quiescent galaxies. and a number of old massive galaxies with super-solar αabundances have been discovered (Thomas et al 2005;Choi et al 2014;Conroy et al 2013;Onodera et al 2015;Kriek et al 2016Kriek et al , 2019Jørgensen et al 2017Jørgensen et al , 2018. Underestimating α-abundance affects the slope of the UV-NIR continuum, where Vazdekis et al (2015) show differences of 10 per cent in optical colours, or 40 per cent in flux within a bandpass, between solar [α/Fe] and +0.4 albeit for galaxies much older than included in our study.…”

“…Although not shown in Figure B1, Leethochawalit et al (2018) study the MZR with respect to [Fe/H] for quiescent galaxies at z∼0.4 using spectral modelling, and recover values consistent with the highest density (purple) region in our plot (see their figure 7). Interestingly, Kriek et al (2019) measure the metallicity of three massive quiescent galaxies at z∼1.4, using high-resolution spectroscopy to measure absorption lines, Figure B1. Metallicity as a function of diffuse dust optical depth (left) and stellar mass (right) for the GOGREEN UVJ -quiescent sample.…”

Half-mass Radii of Quiescent and Star-forming Galaxies Evolve Slowly from 0 ≲ z ≤ 2.5: Implications for Galaxy Assembly Histories*

“…In this case, there would still be additional growth in quiescent half-mass radii that must be accounted for by progenitor growth. A careful study of the half-mass radii of the smallest quiescent galaxies over time (e.g., Carollo et al 2013), potentially in combination with stellar abundance studies (e.g., Kriek et al 2016Kriek et al , 2019, is required to fully understand how much progenitor bias contributes to quiescent half-mass radius growth.…”

Resolved Multi-element Stellar Chemical Abundances in the Brightest Quiescent Galaxy at z ∼ 2

“…However, the faintness of high-z quiescent galaxies makes spectroscopic observations extremely challenging. In recent years, several authors have attempted to extend stellar chemical abundance studies to higher redshifts using a single or stacked spectra of a handful of quiescent galaxies (e.g., Onodera et al 2015;Lonoce et al 2015;Kriek et al 2019;Lonoce et al 2020). Currently, there is only one quiescent galaxy at z ∼ 2 for which [Fe/H] and [Mg/Fe] have been measured to ∼ 0.1 dex precision (COSMOS-11494, Kriek et al 2016).…”