@article{23200,
  abstract     = {We investigate the low-ionization electron density in the interstellar medium (ISM) of galaxies across 0 < z < 8,
derived with the [O II] λλ3727, 3730 and [S II] λλ6718, 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 ne[S II] = + 463 203 cm 281 3
for CONGRESS, ne[S II] = + 301 206 cm 388 3
for FRESCO, and
ne[O II] = + 202 102 cm 145 3
for the NIRSpec/MSA sample. The median low-ionization ne increases from z = 0 to 4,
in agreement with previous studies and those using JWST observations. However, beyond z ∼ 4 median ne begins
to deviate from a monotonically increasing evolution with z. We find a positive, but shallow, correlation between
O32 (a proxy for the ionization parameter) and ne, while also confirming a positive correlation between O32 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.},
  author       = {Stephenson, Mabel G. and Chisholm, John and Saldana-Lopez, A. and Matthee, Jorryt J and Henry, Alaina and Naidu, Rohan P. and Flury, Sophia R. and Hutchison, Taylor A. and Finkelstein, Steven L. and Guseva, Natalia G. and Izotov, Yuri I. and Marques-Chaves, Rui and Oesch, Pascal A. and Reddy, Naveen A. and Schaerer, Daniel},
  issn         = {1538-4357},
  journal      = {The Astrophysical Journal},
  number       = {2},
  publisher    = {IOP Publishing},
  title        = {{The evolution of low-ionization electron densities in galaxies across cosmic epochs}},
  doi          = {10.3847/1538-4357/ae9eb7},
  volume       = {1010},
  year         = {2026},
}