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

Abstract

Measuring the chemical composition of galaxies is crucial to our understanding of galaxy formation and evolution models. However, such measurements are extremely challenging for quiescent galaxies at high redshifts, which have faint stellar continua and compact sizes, making it difficult to detect absorption lines and nearly impossible to spatially resolve them. Gravitational lensing offers the opportunity to study these galaxies with detailed spectroscopy that can be spatially resolved. In this work, we analyze deep spectra of MRG-M0138, a lensed quiescent galaxy at z = 1.98 which is the brightest of its kind, with an H-band magnitude of 17.1. Taking advantage of full spectral fitting, we measure [Mg/Fe] = 0.51 ± 0.05, [Fe/H] = 0.26 ± 0.04, and, for the first time, the stellar abundances of 6 other elements in this galaxy. We further constrained, also for the first time in a z ∼ 2 galaxy, radial gradients in stellar age, [Fe/H], and [Mg/Fe]. We detect no gradient in age or [Mg/Fe] and a slightly negative gradient in [Fe/H], which has a slope comparable to that seen in local early-type galaxies. Our measurements show that not only is MRG-M0138 very Mg-enhanced compared to the centers of local massive early-type galaxies, it is also very iron rich. These dissimilar abundances suggest that even the inner regions of massive galaxies have experienced significant mixing of stars in mergers, in contrast to a purely inside-out growth model. The abundance pattern observed in MRG-M0138 challenges simple galactic chemical evolution models that vary only the star formation timescale and shows the need for more elaborate models.

The Massive Ancient Galaxies at z > 3 NEar-infrared (MAGAZ3NE) Survey: Confirmation of Extremely Rapid Star Formation and Quenching Timescales for Massive Galaxies in the Early Universe*

“…, as several studies have shown this to be broadly correct for highredshift massive galaxies (e.g., Belli et al 2019;Kriek et al 2019;Estrada-Carpenter et al 2019;Jafariyazani et al 2020; but also see P. Saracco et al 2020, in preparation, for a spectroscopic measurement of supersolar stellar metallicity for one of our galaxies, COS-DR3-160748). However, we did test metallicities of…”

An exquisitely deep view of quenching galaxies through the gravitational lens: Stellar population, morphology, and ionized gas

“…Only literature measurements with errors smaller than ∆log(Z /Z ) < 0.3 are shown in Figure 6. The only works presenting stellar metallicity measurements of quiescent galaxies at z > 1.9 are Kriek et al (2016), Newman et al (2018a), andJafariyazani et al (2020). Only one galaxy, MRG-M0150, in the sample of Newman et al ( 2018a) is plotted because we exclude those without lensing models which are needed to constrain the intrinsic M .…”

“…Only one galaxy, MRG-M0150, in the sample of Newman et al ( 2018a) is plotted because we exclude those without lensing models which are needed to constrain the intrinsic M . As for MRG-M0138 we obtain a metallicity 5 based on the abundance measurement presented in Jafariyazani et al (2020) which provided a more detailed analysis than in Newman et al (2018a). As m2129 is part of the sample in this work as well as in Newman et al (2018a), to avoid duplication we only show our measurements here 6 .…”

Massive high-redshift quiescent galaxies with JWST

“…The S/N and spectral coverage of current data at z ∼ 3−5 are insufficient to develop linkages to z ∼ 2 observations of α-enhancements (e.g. Kriek et al 2016) and simultaneous α and Fe enhancements (Jafariyazani et al 2020). Deep rest-UV continuum observations are required to constrain the stellar population properties and ISM conditions of star-forming galaxies at z > 6, which are likely progenitors of massive quiescent galaxies at z ∼ 3−5.…”