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Title: The Impact of Star-formation-rate Surface Density on the Electron Density and Ionization Parameter of High-redshift Galaxies*

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 redshiftszspec≃ 1.9–3.7, we construct composite rest-frame optical spectra in bins of ΣSFRand infer electron densities,ne, using the ratio of the [Oii]λλ3727, 3730 doublet. Our analysis suggests a significant (≃3σ) correlation betweenneand ΣSFR. We further find significant correlations betweenUand ΣSFRfor composite spectra of a subsample of 113 galaxies, and for a smaller sample of 25 individual galaxies with inferences ofU. The increase inne—and possibly also the volume filling factor of dense clumps in Hiiregions—with ΣSFRappear to be important factors in explaining the relationship betweenUand ΣSFR. Further, the increase inneand SFR with redshift at a fixed stellar mass can account for most of the redshift evolution ofU. These results suggest that the gas density, which setsneand 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.

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Author(s) / Creator(s):
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DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Medium: X Size: Article No. 56
["Article No. 56"]
Sponsoring Org:
National Science Foundation
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