Papovich, CaseySimons, Raymond C.Estrada-Carpenter, VicenteMatharu, JasleenMomcheva, IvelinaTrump, Jonathan R.Backhaus, Bren E.Brammer, GabrielCleri, Nikko J.Finkelstein, S. L.Kewley, LisaNicholls, David2026-01-202026-01-200004-637Xhttps://hdl.handle.net/1885/733804762We use deep spectroscopy from the Hubble Space Telescope Wide-Field-Camera 3 IR grisms combined with broadband photometry to study the stellar populations, gas ionization and chemical abundances in star-forming galaxies at z ∼ 1.1-2.3. The data stem from the CANDELS Lyα Emission At Reionization (CLEAR) survey. At these redshifts, the grism spectroscopy measure the [O II] λ λ3727, 3729, [O III]λ λ4959, 5008, and Hβ strong emission features, which constrain the ionization parameter and oxygen abundance of the nebular gas. We compare the line-flux measurements to predictions from updated photoionization models (MAPPINGS V; Kewley et al.), which include an updated treatment of nebular gas pressure, log P / k = n e T e . Compared to low-redshift samples (z ∼ 0.2) at fixed stellar mass, log M * / M ⊙ = 9.4-9.8, the CLEAR galaxies at z = 1.35 (1.90) have lower gas-phase metallicity, Δ ( log Z ) = 0.25 (0.35) dex, and higher ionization parameters, Δ ( log q ) = 0.25 (0.35) dex, where U ≡ q/c. We provide updated analytic calibrations between the [O III], [O II], and Hβ emission-line ratios, metallicity, and ionization parameter. The CLEAR galaxies show that at fixed stellar mass, the gas ionization parameter is correlated with the galaxy specific star formation rates, where Δ log q ≃ 0.4 × Δ ( log sSFR ) , derived from changes in the strength of galaxy Hβ equivalent width. We interpret this as a consequence of higher gas densities, lower gas covering fractions, combined with a higher escape fraction of H-ionizing photons. We discuss both tests to confirm these assertions and implications this has for future observations of galaxies at higher redshifts.This work is supported in part by the National Science Foundation through grant AST 1614668. C.P. thanks Marsha L. and Ralph F. Schilling for generous support of this research. V.E.C. acknowledges support from the NASA Headquarters under the Future Investigators in NASA Earth and Space Science and Technology (FINESST) award 19-ASTRO19-0122, as well as support from the Hagler Institute for Advanced Study at Texas A&M University. I.J. acknowledges support from NASA under award No. 80GSFC21M0002. This work was supported in part by NASA contract NNG16PJ33C, the Studying Cosmic Dawn with WFIRST Science Investigation Team. The authors acknowledge the Texas A&M University Brazos HPC cluster and Texas A&M High Performance Research Computing Resources (HPRC, http://hprc.tamu.edu) that contributed to the research reported here. This work benefited from generous support from the George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University. Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions.application/pdfen-AU© 2022 The Author(s)https://creativecommons.org/licenses/by/4.0/202210.3847/1538-4357/ac80582023-10-22Creative Commons Attribution 4.0 licence