Abstract
We use the large spectroscopic data set of the MOSFIRE Deep Evolution Field survey to investigate some of the key factors responsible for the elevated ionization parameters (U) inferred for high-redshift galaxies, focusing in particular on the role of star-formation-rate surface density (ΣSFR). Using a sample of 317 galaxies with spectroscopic redshifts z spec ≃ 1.9-3.7, we construct composite rest-frame optical spectra in bins of ΣSFR and infer electron densities, n e, using the ratio of the [O ii] λ λ3727, 3730 doublet. Our analysis suggests a significant (≃3σ) correlation between n e and ΣSFR. We further find significant correlations between U and ΣSFR for composite spectra of a subsample of 113 galaxies, and for a smaller sample of 25 individual galaxies with inferences of U. The increase in n e—and possibly also the volume filling factor of dense clumps in H ii regions—with ΣSFR appear to be important factors in explaining the relationship between U and ΣSFR. Further, the increase in n e and SFR with redshift at a fixed stellar mass can account for most of the redshift evolution of U. These results suggest that the gas density, which sets n e and the overall level of star formation activity, may play a more important role than metallicity evolution in explaining the elevated ionization parameters of high-redshift galaxies.
Document Type
Article
Publication Date
2023
Digital Object Identifier (DOI)
https://doi.org/10.3847/1538-4357/acd0b1
Funding Information
We acknowledge support from NSF AAG grants AST1312780, 1312547, 1312764, and 1313171, grant AR13907 from the Space Telescope Science Institute, and grant NNX16AF54G from the NASA ADAP program. This work made use of v2.2.1 of the Binary Population and Spectral Synthesis (BPASS) models as described in Eldridge et al. (2017) and Stanway & Eldridge (2018), and v17.02 of the Cloudy radiative transfer code (Ferland et al. 2017). We wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, most of the observations presented herein would not have been possible.
Repository Citation
Reddy, Naveen; Sanders, Ryan L.; Shapley, Alice E.; Topping, Michael W.; Kriek, Mariska; Coil, Alison L.; Mobasher, Bahram; Siana, Brian; and Rezaee, Saeed, "The Impact of Star-formation-rate Surface Density on the Electron Density and Ionization Parameter of High-redshift Galaxies" (2023). Physics and Astronomy Faculty Publications. 705.
https://uknowledge.uky.edu/physastron_facpub/705
Notes/Citation Information
© 2023. The Author(s). Published by the American Astronomical Society.
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