A Glimpse of the Stellar Populations and Elemental Abundances of Gravitationally Lensed, Quiescent Galaxies at z ≳ 1 with Keck Deep Spectroscopy

Creators: Zhuang, Zhuyun; Leethochawalit, Nicha; Kirby, Evan N.; Nightingale, J. W.; Steidel, Charles C.; Glazebrook, Karl; Barone, Tania M.; Skobe, Hannah; Sweet, Sarah M.; Nanayakkara, Themiya; Allen, Rebecca J.; G. C., Keerthi Vasan; Jones, Tucker; Kacprzak, Glenn G.; Tran, Kim-Vy H.; Jacobs, Colin

Abstract

Gravitational lenses can magnify distant galaxies, allowing us to discover and characterize the stellar populations of intrinsically faint, quiescent galaxies that are otherwise extremely difficult to directly observe at high redshift from ground-based telescopes. Here, we present the spectral analysis of two lensed, quiescent galaxies at z ≳ 1 discovered by the ASTRO 3D Galaxy Evolution with Lenses survey: AGEL1323 (M_* ∼ 10^(11.1)M_⊙, z = 1.016, μ ∼ 14.6) and AGEL0014 (M_* ∼ 10^(11.5)M_⊙, z = 1.374, μ ∼ 4.3). We measured the age, [Fe/H], and [Mg/Fe] of the two lensed galaxies using deep, rest-frame-optical spectra (S/N ≳ 40 Å⁻¹) obtained on the Keck I telescope. The ages of AGEL1323 and AGEL0014 are 5.6^(+0.8)_(−0.8) Gyr and 3.1^(+0.8)_(−0.3) Gyr, respectively, indicating that most of the stars in the galaxies were formed less than 2 Gyr after the Big Bang. Compared to nearby quiescent galaxies of similar masses, the lensed galaxies have lower [Fe/H] and [Mg/H]. Surprisingly, the two galaxies have comparable [Mg/Fe] to similar-mass galaxies at lower redshifts, despite their old ages. Using a simple analytic chemical evolution model connecting the instantaneously recycled element Mg with the mass-loading factors of outflows averaged over the entire star formation history, we found that the lensed galaxies may have experienced enhanced outflows during their star formation compared to lower-redshift galaxies, which may explain why they quenched early.

Additional Information

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. The authors acknowledge the insightful and constructive feedback of the anonymous referee, which helped us improve the manuscript. We would also like to thank Meng Gu for helpful advice on full-spectrum fitting with alf and Allison Strom for useful discussions on MOSFIRE data reduction and analysis with MOSPEC. We gratefully thank the staff at the W. M. Keck Observatory, including support astronomers Luca Rizzi, Carlos Alvarez, and Jim Lyke and telescope operators Arina Rostopchina, Julie Renauld-Kim, and Heather Hershey, for assisting in the observations. We are grateful to the many people who have worked to make the Keck Telescope and its instruments a reality and to operate and maintain the Keck Observatory. The authors wish to extend special thanks to those of Hawaiian ancestry, on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented herein would have been possible. This material is based on work supported by the National Science Foundation under grant Nos. AST-2233781 (E.N.K.) and AST-2009278 (C.C.S.). Z.Z., E.N.K., and C.C.S. acknowledge financial support from National Aeronautics and Space Administration (NASA) through the FINESST program (No. 80NSSC22K1755). K.G., T.N. and C.J. acknowledge support from Australian Research Council (FL180100060). S.M.S. acknowledges funding from the Australian Research Council (DE220100003). T.J. and K.V.G.C. gratefully acknowledge financial support from NASA through grant No. HST-GO-16773, the Gordon and Betty Moore Foundation through grant No. GBMF8549, and the National Science Foundation through grant No. AST-2108515. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project No. CE170100013. This work has made use of observations from the NASA/ESA Hubble Space Telescope obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Support for Program No. GO-16773 was provided through a grant from the STScI under NASA contract NAS5-26555. Facilities: Keck I (LRIS - , MOSFIRE) - , HST (WFC3). - Software: SExtractor (Bertin & Arnouts 1996), alf (Conroy et al. 2018), dynesty (Speagle 2020), PyAutoLens (Nightingale & Dye 2015; Nightingale et al. 2018, 2021a, 2021b), BAGPIPES (Carnall et al. 2018, 2019), Astropy (Astropy Collaboration et al. 2013, 2018), NumPy (Harris et al. 2020), SciPy (Virtanen et al. 2020).

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