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We use deep spectroscopy from the Hubble Space Telescope (HST)Wide-Field-Camera 3 (WFC3) IR grisms combined with broad-band photometry tostudy the stellar populations, gas ionization and chemical abundances instar-forming galaxies at $z\sim 1.1-2.3$. The data stem from the CANDELSLyman-$\alpha$ Emission At Reionization (CLEAR) survey. At these redshifts thegrism spectroscopy measure the [OII] 3727, 3729, [OIII] 4959, 5008, H-$\beta$strong emission features, which constrain the ionization parameter and oxygenabundance of the nebular gas. We compare the line flux measurements topredictions from updated photoionization models (MAPPINGS (Kewley et al. 2019),which include an updated treatment of nebular gas pressure, log P/k = $n_eT_e$. Compared to low-redshift samples ($z\sim 0.2$) at fixed stellar mass,llog M / M$_\odot$ = 9.4-9.8, the CLEAR galaxies at z=1.35 (z=1.90) have lowergas-phase metallicity, $\Delta$(log Z) = 0.25 (0.35) dex, and higher ionizationparameters, $\Delta$(log q) = 0.25 (0.35) dex, where U = q/c. We provideupdated analytic calibrations between the [OIII], [OII], and H-$\beta$ emissionline ratios, metallicity, and ionization parameter. The CLEAR galaxies showthat at fixed stellar mass, the gas ionization parameter is correlated with thegalaxy specific star-formation rates (sSFRs), where $\Delta$ log q = 0.4$\Delta$(log sSFR), derived from changes in the strength of galaxy H-$\beta$equivalent width. We interpret this as a consequence of higher gas densities,lower gas covering fractions, combined with higher escape fraction ofH-ionizing photons. We discuss both tests to confirm these assertions andimplications this has for future observations of galaxies at higher redshifts.

CLEAR: The Ionization and Chemical-Enrichment Properties of Galaxies at 1.1 < z < 2.3