{"article_type":"original","PlanS_conform":"1","DOAJ_listed":"1","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"external_id":{"arxiv":["2608.23846"]},"date_published":"2026-10-15T00:00:00Z","department":[{"_id":"JoMa"}],"file_date_updated":"2026-10-28T08:02:57Z","doi":"10.3847/1538-4357/ae9eb7","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>","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>.","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.","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.","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).","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>.","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>"},"quality_controlled":"1","author":[{"last_name":"Stephenson","full_name":"Stephenson, Mabel G.","first_name":"Mabel G."},{"last_name":"Chisholm","first_name":"John","full_name":"Chisholm, John"},{"last_name":"Saldana-Lopez","first_name":"A.","full_name":"Saldana-Lopez, A."},{"full_name":"Matthee, Jorryt J","first_name":"Jorryt J","last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720","orcid":"0000-0003-2871-127X"},{"last_name":"Henry","full_name":"Henry, Alaina","first_name":"Alaina"},{"full_name":"Naidu, Rohan P.","first_name":"Rohan P.","last_name":"Naidu"},{"last_name":"Flury","first_name":"Sophia R.","full_name":"Flury, Sophia R."},{"last_name":"Hutchison","first_name":"Taylor A.","full_name":"Hutchison, Taylor A."},{"full_name":"Finkelstein, Steven L.","first_name":"Steven L.","last_name":"Finkelstein"},{"first_name":"Natalia G.","full_name":"Guseva, Natalia G.","last_name":"Guseva"},{"last_name":"Izotov","full_name":"Izotov, Yuri I.","first_name":"Yuri I."},{"full_name":"Marques-Chaves, Rui","first_name":"Rui","last_name":"Marques-Chaves"},{"first_name":"Pascal A.","full_name":"Oesch, Pascal A.","last_name":"Oesch"},{"full_name":"Reddy, Naveen A.","first_name":"Naveen A.","last_name":"Reddy"},{"full_name":"Schaerer, Daniel","first_name":"Daniel","last_name":"Schaerer"}],"OA_place":"publisher","status":"public","publisher":"IOP Publishing","date_created":"2026-10-27T10:40:40Z","day":"15","ddc":["520"],"_id":"23200","language":[{"iso":"eng"}],"oa_version":"Published Version","scopus_import":"1","fulldoi":"https://doi.org/10.3847/1538-4357/ae9eb7","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","oa":1,"publication_status":"published","tmp":{"short":"CC BY (4.0)","image":"/images/cc_by.png","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"volume":1010,"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."}],"year":"2026","title":"The evolution of low-ionization electron densities in galaxies across cosmic epochs","intvolume":"      1010","has_accepted_license":"1","publication":"The Astrophysical Journal","arxiv":1,"date_updated":"2026-10-28T08:05:42Z","month":"10","file":[{"relation":"main_file","success":1,"creator":"dernst","checksum":"6968c85ac6ccc997a30dab818dc04e42","content_type":"application/pdf","date_created":"2026-10-28T08:02:57Z","file_size":4194012,"access_level":"open_access","file_id":"23202","file_name":"2026_AstrophysicalJour_Stephenson.pdf","date_updated":"2026-10-28T08:02:57Z"}],"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).","issue":"2","article_number":"184","das_tickbox":"0","type":"journal_article","article_processing_charge":"Yes","OA_type":"gold"}