Abstract
We examine the factors responsible for the variation in the ionization parameter (U) of high-redshift star-forming galaxies based on medium-resolution JWST/NIRSpec observations obtained by the Cosmic Evolution Early Release Science survey. The sample consists of 48 galaxies with redshifts zspec = 2.7−6.3, which are largely representative of typical galaxies at these redshifts. The [S II] λλ6718, 6733 doublet is used to estimate electron densities (n e), and dust-corrected Hα luminosities are used to compute ionizing photon rates (Q). Using composite spectra of galaxies in bins of [O III] λλ4960, 5008/[O II] λλ3727, 3730 (O32) as a proxy for U, we determine that galaxies with higher O32 have 〈n e〉 ; 500 cm−3 that are 5 × larger than that of lower-O32 galaxies. We do not find a significant difference in 〈Q〉 between low-and high-O32 galaxies. Photoionization modeling indicates a large spread in Ulog of ≈1.5 dex at a fixed Zneb . On the other hand, the data indicate a highly significant correlation between U and star-formation-rate surface density (ΣSFR), which appears to be redshift invariant at z ∼ 1.6−6.3, and possibly up to z ∼ 9.5. We consider several avenues through which metallicity and ΣSFR (or gas density) may influence U, including variations in n e and Q, internal dust extinction of ionizing photons, and the effects of gas density on the volume filling fraction. Based on these considerations, we conclude that gas density may play a more central role than metallicity in modulating U at these redshifts.
Document Type
Article
Publication Date
2023
Digital Object Identifier (DOI)
https://doi.org/10.3847/1538-4357/acd754
Funding Information
Support for this work was also provided through the NASA Hubble Fellowship grant HST-HF2-51469.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. The Cosmic Dawn Center is funded by the Danish National Research Foundation (DNRF) under grant No. 140. Cloud-based data processing and file storage for this work is provided by the AWS Cloud Credits for Research program.
Repository Citation
Reddy, Naveen; Topping, Michael W.; Sanders, Ryan L.; Shapley, Alice E.; and Brammer, Gabriel B., "A JWST/NIRSpec Exploration of the Connection between Ionization Parameter, Electron Density, and Star-formation-rate Surface Density in z = 2.7–6.3 Galaxies" (2023). Physics and Astronomy Faculty Publications. 691.
https://uknowledge.uky.edu/physastron_facpub/691
Notes/Citation Information
© 2023. The Author(s). Published by the American Astronomical Society.
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