Year: 2026
Type: article
Abstract: We investigate the low-ionization electron density in the interstellar medium (ISM) of galaxies across 0 < z < 8, derived with the [O ii ] λλ 3727, 3730 and [S ii ] λλ 6718, 6733 doublets, using both deep JWST/NIRCam/grism and NIRSpec/MSA spectroscopy. Along with ancillary density samples from the literature at 0 < z < 6, we assemble three samples containing a total of 703 galaxies spanning 3.7 < z < 7.8 at 〈 z 〉 ∼ 5.6; 691 galaxies in the luminosity-complete NIRCam/grism programs CONGRESS and FRESCO at 〈 z 〉 ∼ 4.3 and ∼5.3, respectively; and 12 galaxies with high-resolution NIRSpec/MSA spectra from the GO 1871 and GLASS programs. We find median electron densities of n e [S ii ] = 46 3 − 203 + 281 cm − 3 for CONGRESS, n e [S ii ] = 30 1 − 206 + 388 cm − 3 for FRESCO, and n e [O ii ] = 20 2 − 102 + 145 cm − 3 for the NIRSpec/MSA sample. The median low-ionization n e increases from z = 0 to 4, in agreement with previous studies and those using JWST observations. However, beyond z ∼ 4 median n e begins to deviate from a monotonically increasing evolution with z . We find a positive, but shallow, correlation between O 32 (a proxy for the ionization parameter) and n e , while also confirming a positive correlation between O 32 and z . We suggest that these trends are possibly due to an evolving ISM gas density and ionization structure, and propose a toy model where the gas clumping evolves with z to explain the observed density and ionization variations.
Source: The Astrophysical Journal
Institutions: The University of Texas at Austin, Stockholm University, Institute of Science and Technology Austria, Space Telescope Science Institute, Massachusetts Institute of Technology, University of Edinburgh, Goddard Space Flight Center, University of Maryland, College Park, National Academy of Sciences of Ukraine, University of Geneva, University of Copenhagen, University of California, Riverside, Centre National de la Recherche Scientifique
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Funders: National Science Foundation, National Aeronautics and Space Administration, Oak Ridge Associated Universities, Space Telescope Science Institute, National Research Foundation, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Danmarks Grundforskningsfond, Knut och Alice Wallenbergs Stiftelse, Goddard Space Flight Center, Staatssekretariat für Bildung, Forschung und Innovation
OpenAlex ID: W7203676928
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