---
DOAJ_listed: '1'
OA_place: publisher
OA_type: gold
PlanS_conform: '1'
_id: '23200'
abstract:
- lang: eng
  text: "We investigate the low-ionization electron density in the interstellar medium
    (ISM) of galaxies across 0 < z < 8,\r\nderived with the [O II] λλ3727, 3730 and
    [S II] λλ6718, 6733 doublets, using both deep JWST/NIRCam/grism\r\nand NIRSpec/MSA
    spectroscopy. Along with ancillary density samples from the literature at 0 <
    z < 6, we\r\nassemble three samples containing a total of 703 galaxies spanning
    3.7 < z < 7.8 at 〈z〉 ∼ 5.6; 691 galaxies in the\r\nluminosity-complete NIRCam/grism
    programs CONGRESS and FRESCO at 〈z〉 ∼ 4.3 and ∼5.3, respectively;\r\nand 12 galaxies
    with high-resolution NIRSpec/MSA spectra from the GO 1871 and GLASS programs.
    We find\r\nmedian electron densities of ne[S II] = + 463 203 cm 281 3\r\nfor CONGRESS,
    ne[S II] = + 301 206 cm 388 3\r\nfor FRESCO, and\r\nne[O II] = + 202 102 cm 145
    3\r\nfor the NIRSpec/MSA sample. The median low-ionization ne increases from z
    = 0 to 4,\r\nin agreement with previous studies and those using JWST observations.
    However, beyond z ∼ 4 median ne begins\r\nto deviate from a monotonically increasing
    evolution with z. We find a positive, but shallow, correlation between\r\nO32
    (a proxy for the ionization parameter) and ne, while also confirming a positive
    correlation between O32 and z.\r\nWe suggest that these trends are possibly due
    to an evolving ISM gas density and ionization structure, and\r\npropose a toy
    model where the gas clumping evolves with z to explain the observed density and
    ionization\r\nvariations."
acknowledgement: "We are grateful for the support for programs GO 1871, GO 1895, and
  GO 3577 provided by NASA through a grant from the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in Astronomy,
  Inc., under NASA contract NAS 5-03127. This work is based in part on observations
  made with the NASA/ESA/CSA JWST. The data were obtained from the Mikulski Archive
  for Space Telescopes at the Space Telescope Science Institute, which is operated
  by the Association of Universities for Research in Astronomy, Inc., under NASA contract
  NAS 5-03127 for JWST. These observations are associated with programs GO 1324, GO
  1871, GO 1895 and GO 3577. The specific observations analyzed can be accessed via
  DOI: 10.17909/01dt-fm17.\r\n\r\nA.S.L. acknowledges support from Knut and Alice
  Wallenberg Foundation. T.A.H. acknowledges support from an appointment to the NASA
  Postdoctoral Program at the NASA Goddard Space, administered by Oak Ridge Associated
  Universities under contract with NASA, as well as the University of Maryland Baltimore
  County and the Center for Space Sciences and Technology. N.G.G. and Y.I.I. and acknowledge
  support from the joint Ukrainian-Swiss project No. 224866. This work has received
  funding from the Swiss State Secretariat for Education, Research, and Innovation
  (SERI) under contract number MB22.00072, as well as from the Swiss National Science
  Foundation (SNSF) through project grant 200020_207349. The Cosmic Dawn Center (DAWN)
  is funded by the Danish National Research Foundation under grant DNRF140.\r\n\r\nFacility:
  JWST (NIRCam - , NIRSpec).\r\n\r\nSoftware: numpy (v.1.24.3; C. R. Harris et al.
  2020), scipy (v.1.13.1; P. Virtanen et al. 2020), astropy (Astropy Collaboration
  et al. 2013, 2018, 2022), pyneb (v.1.1.24; V. Luridiana et al. 2013, 2015; C. Morisset
  et al. 2020), msaexp (v.0.8.4; G. B. Brammer 2022), msafit (A. de Graaff et al.
  2024), grizli (G. Brammer 2018), EAZY (G. B. Brammer et al. 2008), BAGPIPES (A.
  C. Carnall et al. 2018), Prospector (B. D. Johnson et al. 2019, 2021), pysersic
  (I. Pasha & T. B. Miller 2023), GALFIT (C. Y. Peng et al. 2002, 2010), kendall (S.
  R. Flury et al. 2022; S. R. Flury 2023)."
article_number: '184'
article_processing_charge: Yes
article_type: original
arxiv: 1
author:
- first_name: Mabel G.
  full_name: Stephenson, Mabel G.
  last_name: Stephenson
- first_name: John
  full_name: Chisholm, John
  last_name: Chisholm
- first_name: A.
  full_name: Saldana-Lopez, A.
  last_name: Saldana-Lopez
- first_name: Jorryt J
  full_name: Matthee, Jorryt J
  id: 7439a258-f3c0-11ec-9501-9df22fe06720
  last_name: Matthee
  orcid: 0000-0003-2871-127X
- first_name: Alaina
  full_name: Henry, Alaina
  last_name: Henry
- first_name: Rohan P.
  full_name: Naidu, Rohan P.
  last_name: Naidu
- first_name: Sophia R.
  full_name: Flury, Sophia R.
  last_name: Flury
- first_name: Taylor A.
  full_name: Hutchison, Taylor A.
  last_name: Hutchison
- first_name: Steven L.
  full_name: Finkelstein, Steven L.
  last_name: Finkelstein
- first_name: Natalia G.
  full_name: Guseva, Natalia G.
  last_name: Guseva
- first_name: Yuri I.
  full_name: Izotov, Yuri I.
  last_name: Izotov
- first_name: Rui
  full_name: Marques-Chaves, Rui
  last_name: Marques-Chaves
- first_name: Pascal A.
  full_name: Oesch, Pascal A.
  last_name: Oesch
- first_name: Naveen A.
  full_name: Reddy, Naveen A.
  last_name: Reddy
- first_name: Daniel
  full_name: Schaerer, Daniel
  last_name: Schaerer
citation:
  ama: Stephenson MG, Chisholm J, Saldana-Lopez A, et al. The evolution of low-ionization
    electron densities in galaxies across cosmic epochs. <i>The Astrophysical Journal</i>.
    2026;1010(2). doi:<a href="https://doi.org/10.3847/1538-4357/ae9eb7">10.3847/1538-4357/ae9eb7</a>
  apa: Stephenson, M. G., Chisholm, J., Saldana-Lopez, A., Matthee, J. J., Henry,
    A., Naidu, R. P., … Schaerer, D. (2026). The evolution of low-ionization electron
    densities in galaxies across cosmic epochs. <i>The Astrophysical Journal</i>.
    IOP Publishing. <a href="https://doi.org/10.3847/1538-4357/ae9eb7">https://doi.org/10.3847/1538-4357/ae9eb7</a>
  chicago: Stephenson, Mabel G., John Chisholm, A. Saldana-Lopez, Jorryt J Matthee,
    Alaina Henry, Rohan P. Naidu, Sophia R. Flury, et al. “The Evolution of Low-Ionization
    Electron Densities in Galaxies across Cosmic Epochs.” <i>The Astrophysical Journal</i>.
    IOP Publishing, 2026. <a href="https://doi.org/10.3847/1538-4357/ae9eb7">https://doi.org/10.3847/1538-4357/ae9eb7</a>.
  ieee: M. G. Stephenson <i>et al.</i>, “The evolution of low-ionization electron
    densities in galaxies across cosmic epochs,” <i>The Astrophysical Journal</i>,
    vol. 1010, no. 2. IOP Publishing, 2026.
  ista: Stephenson MG, Chisholm J, Saldana-Lopez A, Matthee JJ, Henry A, Naidu RP,
    Flury SR, Hutchison TA, Finkelstein SL, Guseva NG, Izotov YI, Marques-Chaves R,
    Oesch PA, Reddy NA, Schaerer D. 2026. The evolution of low-ionization electron
    densities in galaxies across cosmic epochs. The Astrophysical Journal. 1010(2),
    184.
  mla: Stephenson, Mabel G., et al. “The Evolution of Low-Ionization Electron Densities
    in Galaxies across Cosmic Epochs.” <i>The Astrophysical Journal</i>, vol. 1010,
    no. 2, 184, IOP Publishing, 2026, doi:<a href="https://doi.org/10.3847/1538-4357/ae9eb7">10.3847/1538-4357/ae9eb7</a>.
  short: M.G. Stephenson, J. Chisholm, A. Saldana-Lopez, J.J. Matthee, A. Henry, R.P.
    Naidu, S.R. Flury, T.A. Hutchison, S.L. Finkelstein, N.G. Guseva, Y.I. Izotov,
    R. Marques-Chaves, P.A. Oesch, N.A. Reddy, D. Schaerer, The Astrophysical Journal
    1010 (2026).
das_tickbox: '0'
date_created: 2026-10-27T10:40:40Z
date_published: 2026-10-15T00:00:00Z
date_updated: 2026-10-28T08:05:42Z
day: '15'
ddc:
- '520'
department:
- _id: JoMa
doi: 10.3847/1538-4357/ae9eb7
external_id:
  arxiv:
  - '2608.23846'
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fulldoi: https://doi.org/10.3847/1538-4357/ae9eb7
has_accepted_license: '1'
intvolume: '      1010'
issue: '2'
language:
- iso: eng
license: https://creativecommons.org/licenses/by/4.0/
month: '10'
oa: 1
oa_version: Published Version
publication: The Astrophysical Journal
publication_identifier:
  eissn:
  - 1538-4357
  issn:
  - 0004-637X
publication_status: published
publisher: IOP Publishing
quality_controlled: '1'
scopus_import: '1'
status: public
title: The evolution of low-ionization electron densities in galaxies across cosmic
  epochs
tmp:
  image: /images/cc_by.png
  legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
  name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
  short: CC BY (4.0)
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 1010
year: '2026'
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