TY - JOUR

T1 - CLEAR

T2 - The Ionization and Chemical-enrichment Properties of Galaxies at 1.1 < z < 2.3

AU - Papovich, Casey

AU - Simons, Raymond C.

AU - Estrada-Carpenter, Vicente

AU - Matharu, Jasleen

AU - Momcheva, Ivelina

AU - Trump, Jonathan R.

AU - Backhaus, Bren E.

AU - Brammer, Gabriel

AU - Cleri, Nikko J.

AU - Finkelstein, Steven L.

AU - Giavalisco, Mauro

AU - Ji, Zhiyuan

AU - Jung, Intae

AU - Kewley, Lisa J.

AU - Nicholls, David C.

AU - Pirzkal, Norbert

AU - Rafelski, Marc

AU - Weiner, Benjamin

N1 - Publisher Copyright: © 2022. The Author(s). Published by the American Astronomical Society.

PY - 2022/9/20

Y1 - 2022/9/20

N2 - We 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.

AB - We 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.

U2 - 10.3847/1538-4357/ac8058

DO - 10.3847/1538-4357/ac8058

M3 - Journal article

AN - SCOPUS:85139431312

VL - 937

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0067-0049

IS - 1

M1 - 22

ER -