High-z quiescent galaxies

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.

In Zhuang et al. (2023), we present the spectral analysis of two lensed, quiescent galaxies at $z\gtrsim 1$ discovered by the ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey: AGEL1323 (\(M_*\sim 10^{11.1}M_{\odot}\), \(z=1.016\), \(\mu \sim 14.6\)) and AGEL0014 (\(M_*\sim 10^{11.5}M_{\odot}\), \(z=1.374\), \(\mu \sim 4.3\)). We measured the age, [Fe/H], and [Mg/Fe] of the two lensed galaxies using deep, rest-frame-optical spectra obtained on the Keck I telescope. The ages of AGEL1323 andAGEL0014 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.

Our sample (Zhuang et al., 2023) adds two valuable targets to the very limited database of the high-z quiescent galaxies with available stellar [Fe/H] and [Mg/Fe] measurements. Compared to nearby quiescent galaxies of similar masses, the lensed galaxies have lower [Fe/H]. Surprisingly, the two galaxies have comparable [Mg/Fe] to similar-mass galaxies at lower redshifts, despite their old ages, which implies that their SFHs are not significantly different from those of the massive ellipticals in the local universe.

Using a simple analytic chemical evolution model presented in Leethochawalit et al. 2019, we inferred the mass-loading factors of outflows (η) averaged over the entire star formation history from the abundance of the instantaneously recycled element Mg. We find that the AGEL galaxies and other quiescent galaxies at z>1 have higher mass-loading factors than their local counterparts at similar masses, suggesting that these galaxies may have experienced enhanced outflows during their star formation, leading to their early quenching.