CLEAR. I. Ages and Metallicities of Quiescent Galaxies at 1.0 < z < 1.8 Derived from Deep Hubble Space Telescope Grism Data
Estrada-Carpenter 2019
Estrada-Carpenter et al. 2019, ApJ, 870, 133

Using a forward modeling technique, we fit the stellar populations of a sample of 31 massive quiescent galaxies in the CLEAR survey, in a redshift range of 1 < z < 1.8. Our measurements indicate that massive quiescent galaxies in this redshift range have ~ solar stellar metallicities. Thus, there is no evolution in the stellar metallicity - mass relation, up to a redshift of z ~ 1.8. We also show that many of these galaxies had formed ~70% of their stellar mass by z ~ 2-3.

CLEAR II: Evidence for Early Formation of the Most Compact Quiescent Galaxies at High Redshift
Estrada-Carpenter 2020
Estrada-Carpenter et al. 2020, ApJ, 898, 171

Combining photometric, G102 grism, and G141 grism data, we constrain the stellar populations and derive "non-parametric" star-formation histories for a sample of 97 massive quiescent galaxies in the CLEAR survey, in a redshift range of 0.8 < z < 2.5. By comparing formation redshifts (where the galaxy formed half its mass) to stellar surface mass densities within 1 kiloparsec we see that the most compact galaxies are biased to form early (z>2.5), while less compact galaxies show a wide range of formation redshifts. Our results favor a scenario where compact galaxies formed rapidly at high redshift, then go through subsequent evolution through minor mergers.

CLEAR: Paschen-β Star Formation Rates and Dust Attenuation of Low Redshift Galaxies
Cleri 2020
Cleri et al. 2020, arXiv:2009.00617

We use HST G141 grism Paβ (1282 nm) observations to study star formation rates and dust attenuation properties of 32 galaxies of z < 0.287 in the CLEAR survey. We compare Paβ SFRs to more commonly used star formation indicators, including UV continuum and Hα emission. Our measurements indicate that Paβ reveals star formation obscured by regions optically thick to Balmer and UV emission. We also observe burstier star formation histories at lower stellar mass, indicated by higher scatter in Paβ/UV measurements at lower stellar mass (left). Our measurements also suggest that Paβ/Hα ratios are more reliable attenuation indicators than the Balmer decrement. Paβ is minimally attenuated in highly dusty galaxies, while both Hα and Hβ are significantly attenuated.

CLEAR: The Gas-Phase Metallicity Gradients of Star-forming Galaxies at 0.6 < z < 2.6
Simons 2020
Simons et al. 2020, arXiv:2011.03553

Using emission line maps generated from the CLEAR grism observations, we fit the resolved gas-phase metallicities of several hundred normal star-forming galaxies at 0.6 < z < 2.5. Surprisingly, we find that the majority of galaxies over this redshift range have flat radial metallicity gradients---they are as metal-rich in their outer parts as they are in their inner parts. This result rests in stark contrast with today's galaxies, which generally have declining metallicity gradients. It also runs counter to simple expectations from star-formation and stellar evolution models that assume little to no radial migration of gas; such models predict that galaxies should rapidly (<100 Myr) develop declining metallicity gradients. That the majority of these galaxies generally show flat gradients strongly favors a scenario in which gas-phase metals are (re-)distributed around high-redshift galaxies (and/or their central metallicities are diluted through pristine intergalactic accretion) on continuous short timescales.

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