---
OA_place: publisher
OA_type: diamond
PlanS_conform: '1'
_id: '21342'
abstract:
- lang: eng
  text: "JWST has revealed a stunning population of bright galaxies at surprisingly
    early epochs, z > 10,\r\nwhere few such sources were expected. Here we present
    the most distant example of this class yet – MoM-z14, a luminous (MUV = −20.2)
    source in the COSMOS legacy field at zspec = 14.44+0.02−0.02 that expands the
    observational frontier to a mere 280 million years after the Big Bang. The redshift
    is confirmed with NIRSpec/prism spectroscopy through a sharp Lyman-α break and
    ≈ 3σ detections of five rest-UV emission lines. The number density of bright zspec
    ≈ 14 − 15 sources implied by our “Mirage or Miracle” survey spanning ≈ 350 arcmin2
    is > 100× larger (182+329 −105×) than pre-JWST consensus models. The high EWs
    of UV lines (≈15−35˚A) signal a rising star-formation history, with a ≈10× increase
    in the last 5 Myr (SFR5Myr/SFR50Myr = 9.9 +3.0 −5.8). The source is extremely
    compact (circularized re = 74+15\r\n−12 pc), and yet elongated (b/a = 0.25+0.11−0.06),
    suggesting an AGN is not the dominant source of UV light. The steep UV slope (β
    = −2.5 +0.2 −0.2) implies negligible dust attenuation\r\nand a young stellar population.
    The absence of a strong damping wing provides tentative evidence that the immediate
    surroundings of MoM-z14 may be partially ionized at a redshift where virtually
    every reionization model predicts a ≈ 100% neutral fraction. The nitrogen emission
    and highly supersolar [N/C]> 1 hint at an abundance pattern similar to local globular
    clusters that may have once hosted luminous supermassive stars. Since this abundance
    pattern is also common among the most ancient stars born in the Milky Way, we
    may be directly witnessing the formation of such stars in dense clusters, connecting
    galaxy evolution across the entire sweep of cosmic time. "
acknowledgement: "We thank the two anonymous referees for their insightful comments
  that have strengthened this work. “Mirage or Miracle” is but the latest link in
  a long chain of surveys that have built COSMOS into a premier extragalactic legacy
  field. We are thankful to all the teams who have contributed to this legacy, particularly
  those mentioned in §3 for leading recent JWST programs whose imaging\r\nwe have
  incorporated in our analysis. We are grateful to Vasily Belokurov for help in compiling
  the Milky Way reference sample featured in Fig 8. We thank Danielle Berg for sharing
  a highly complete, highly decimalized NUV vacuum line list. We are grateful to our
  program’s NIRSpec reviewer, Dan Coe, and program coordinator, Allison Vick, for
  valuable input on our MSA design. We acknowledge illuminating conversations with
  Risa Wechsler and Chao-Lin Kuo about early reionization. RPN thanks Neil Pappalardo
  and Jane Pappalardo for their generous support of the MIT Pappalardo Fellowships
  in Physics, and for their enthusiasm and encouragement for seeking galaxies at the
  highest redshifts. RPN acknowledges funding from JWST program GO5224. Support for
  this work was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51515.001-A
  awarded by the Space Telescope Science Institute, which is operated by the Association
  of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.
  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. Funded by
  the European Union (ERC, AGENTS, 101076224 and HEAVYMETAL, 101071865). Views and
  opinions expressed are however those of the author(s) only and do not necessarily
  reflect those of\r\nthe European Union or the European Research Council. Neither
  the European Union nor the granting authority can be held responsible for them.
  The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation
  under grant DNRF140. This work has also been supported by JSPS KAKENHI Grant Number
  23H00131. HA acknowledges support from CNES, focused on the JWST mission, and the
  Programme National Cosmology and Galaxies (PNCG)\r\nof CNRS/INSU with INP and IN2P3,
  co-funded by CEA and CNES. HA is supported by the French National Research Agency
  (ANR) under the project FIRSTGAL, grant number ANR-24-CE31-0838. SB is supported
  by the UK Research and Innovation (UKRI) Future Leaders Fellowship [grant number
  MR/V023381/1]. R.D. acknowledges support from the INAF GO 2022\r\ngrant “The birth
  of the giants: JWST sheds light on the build-up of quasars at cosmic dawn” and by
  the PRIN MUR “2022935STW”, RFF M4.C2.1.1, CUP J53D23001570006 and C53D23000950006.
  Computations supporting this paper were run on MIT’s Engaging cluster. This publication
  made use of the NASA Astrophysical Data System for bibliographic information. Some
  of the data products presented herein were retrieved from the Dawn JWST Archive
  (DJA). DJA is an initiative of the Cosmic Dawn Center (DAWN), which is funded by
  the Danish National Research Foundation under grant DNRF140. Software used in developing
  this work includes: matplotlib (Hunter 2007), jupyter (Kluyver et al. 2016), IPython
  (P´erez & Granger 2007), numpy (Oliphant 2015), scipy (Virtanen et al. 2020), TOPCAT
  (Taylor 2005), and Astropy (Astropy Collaboration et al. 2013).This work is based
  on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data
  were obtained from the Mikulski Archive for Space\r\nTelescopes 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 program # 5224."
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: Rohan P.
  full_name: Naidu, Rohan P.
  last_name: Naidu
- first_name: Pascal A.
  full_name: Oesch, Pascal A.
  last_name: Oesch
- first_name: Gabriel
  full_name: Brammer, Gabriel
  last_name: Brammer
- first_name: Andrea
  full_name: Weibel, Andrea
  last_name: Weibel
- first_name: Yijia
  full_name: Li, Yijia
  last_name: Li
- 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: John
  full_name: Chisholm, John
  last_name: Chisholm
- first_name: Clara L.
  full_name: Pollock, Clara L.
  last_name: Pollock
- first_name: Kasper E.
  full_name: Heintz, Kasper E.
  last_name: Heintz
- first_name: Benjamin D.
  full_name: Johnson, Benjamin D.
  last_name: Johnson
- first_name: Xuejian
  full_name: Shen, Xuejian
  last_name: Shen
- first_name: Raphael E.
  full_name: Hviding, Raphael E.
  last_name: Hviding
- first_name: Joel
  full_name: Leja, Joel
  last_name: Leja
- first_name: Sandro
  full_name: Tacchella, Sandro
  last_name: Tacchella
- first_name: Arpita
  full_name: Ganguly, Arpita
  last_name: Ganguly
- first_name: Callum
  full_name: Witten, Callum
  last_name: Witten
- first_name: Hakim
  full_name: Atek, Hakim
  last_name: Atek
- first_name: Sirio
  full_name: Belli, Sirio
  last_name: Belli
- first_name: Sownak
  full_name: Bose, Sownak
  last_name: Bose
- first_name: Rychard
  full_name: Bouwens, Rychard
  last_name: Bouwens
- first_name: Pratika
  full_name: Dayal, Pratika
  last_name: Dayal
- first_name: Roberto
  full_name: Decarli, Roberto
  last_name: Decarli
- first_name: Anna
  full_name: De Graaff, Anna
  last_name: De Graaff
- first_name: Yoshinobu
  full_name: Fudamoto, Yoshinobu
  last_name: Fudamoto
- first_name: Emma
  full_name: Giovinazzo, Emma
  last_name: Giovinazzo
- first_name: Jenny E.
  full_name: Greene, Jenny E.
  last_name: Greene
- first_name: Garth
  full_name: Illingworth, Garth
  last_name: Illingworth
- first_name: Akio K.
  full_name: Inoue, Akio K.
  last_name: Inoue
- first_name: Sarah G.
  full_name: Kane, Sarah G.
  last_name: Kane
- first_name: Ivo
  full_name: Labbe, Ivo
  last_name: Labbe
- first_name: Ecaterina
  full_name: Leonova, Ecaterina
  last_name: Leonova
- first_name: Rui
  full_name: Marques-Chaves, Rui
  last_name: Marques-Chaves
- first_name: Romain A.
  full_name: Meyer, Romain A.
  last_name: Meyer
- first_name: Erica J.
  full_name: Nelson, Erica J.
  last_name: Nelson
- first_name: Guido
  full_name: Roberts-Borsani, Guido
  last_name: Roberts-Borsani
- first_name: Daniel
  full_name: Schaerer, Daniel
  last_name: Schaerer
- first_name: Robert A.
  full_name: Simcoe, Robert A.
  last_name: Simcoe
- first_name: Mauro
  full_name: Stefanon, Mauro
  last_name: Stefanon
- first_name: Yuma
  full_name: Sugahara, Yuma
  last_name: Sugahara
- first_name: Sune
  full_name: Toft, Sune
  last_name: Toft
- first_name: Arjen
  full_name: Van Der Wel, Arjen
  last_name: Van Der Wel
- first_name: Pieter
  full_name: Van Dokkum, Pieter
  last_name: Van Dokkum
- first_name: Fabian
  full_name: Walter, Fabian
  last_name: Walter
- first_name: Darach
  full_name: Watson, Darach
  last_name: Watson
- first_name: John R.
  full_name: Weaver, John R.
  last_name: Weaver
- first_name: Katherine E.
  full_name: Whitaker, Katherine E.
  last_name: Whitaker
citation:
  ama: 'Naidu RP, Oesch PA, Brammer G, et al. A cosmic miracle: A remarkably luminous
    galaxy at zspec = 14.44 confirmed with JWST. <i>The Open Journal of Astrophysics</i>.
    2026;9. doi:<a href="https://doi.org/10.33232/001c.156033">10.33232/001c.156033</a>'
  apa: 'Naidu, R. P., Oesch, P. A., Brammer, G., Weibel, A., Li, Y., Matthee, J. J.,
    … Whitaker, K. E. (2026). A cosmic miracle: A remarkably luminous galaxy at zspec
    = 14.44 confirmed with JWST. <i>The Open Journal of Astrophysics</i>. Maynooth
    Academic Publishing. <a href="https://doi.org/10.33232/001c.156033">https://doi.org/10.33232/001c.156033</a>'
  chicago: 'Naidu, Rohan P., Pascal A. Oesch, Gabriel Brammer, Andrea Weibel, Yijia
    Li, Jorryt J Matthee, John Chisholm, et al. “A Cosmic Miracle: A Remarkably Luminous
    Galaxy at Zspec = 14.44 Confirmed with JWST.” <i>The Open Journal of Astrophysics</i>.
    Maynooth Academic Publishing, 2026. <a href="https://doi.org/10.33232/001c.156033">https://doi.org/10.33232/001c.156033</a>.'
  ieee: 'R. P. Naidu <i>et al.</i>, “A cosmic miracle: A remarkably luminous galaxy
    at zspec = 14.44 confirmed with JWST,” <i>The Open Journal of Astrophysics</i>,
    vol. 9. Maynooth Academic Publishing, 2026.'
  ista: 'Naidu RP, Oesch PA, Brammer G, Weibel A, Li Y, Matthee JJ, Chisholm J, Pollock
    CL, Heintz KE, Johnson BD, Shen X, Hviding RE, Leja J, Tacchella S, Ganguly A,
    Witten C, Atek H, Belli S, Bose S, Bouwens R, Dayal P, Decarli R, De Graaff A,
    Fudamoto Y, Giovinazzo E, Greene JE, Illingworth G, Inoue AK, Kane SG, Labbe I,
    Leonova E, Marques-Chaves R, Meyer RA, Nelson EJ, Roberts-Borsani G, Schaerer
    D, Simcoe RA, Stefanon M, Sugahara Y, Toft S, Van Der Wel A, Van Dokkum P, Walter
    F, Watson D, Weaver JR, Whitaker KE. 2026. A cosmic miracle: A remarkably luminous
    galaxy at zspec = 14.44 confirmed with JWST. The Open Journal of Astrophysics.
    9.'
  mla: 'Naidu, Rohan P., et al. “A Cosmic Miracle: A Remarkably Luminous Galaxy at
    Zspec = 14.44 Confirmed with JWST.” <i>The Open Journal of Astrophysics</i>, vol.
    9, Maynooth Academic Publishing, 2026, doi:<a href="https://doi.org/10.33232/001c.156033">10.33232/001c.156033</a>.'
  short: R.P. Naidu, P.A. Oesch, G. Brammer, A. Weibel, Y. Li, J.J. Matthee, J. Chisholm,
    C.L. Pollock, K.E. Heintz, B.D. Johnson, X. Shen, R.E. Hviding, J. Leja, S. Tacchella,
    A. Ganguly, C. Witten, H. Atek, S. Belli, S. Bose, R. Bouwens, P. Dayal, R. Decarli,
    A. De Graaff, Y. Fudamoto, E. Giovinazzo, J.E. Greene, G. Illingworth, A.K. Inoue,
    S.G. Kane, I. Labbe, E. Leonova, R. Marques-Chaves, R.A. Meyer, E.J. Nelson, G.
    Roberts-Borsani, D. Schaerer, R.A. Simcoe, M. Stefanon, Y. Sugahara, S. Toft,
    A. Van Der Wel, P. Van Dokkum, F. Walter, D. Watson, J.R. Weaver, K.E. Whitaker,
    The Open Journal of Astrophysics 9 (2026).
date_created: 2026-02-22T23:01:35Z
date_published: 2026-01-30T00:00:00Z
date_updated: 2026-02-24T07:37:17Z
day: '30'
ddc:
- '520'
department:
- _id: JoMa
doi: 10.33232/001c.156033
external_id:
  arxiv:
  - '2505.11263'
has_accepted_license: '1'
intvolume: '         9'
language:
- iso: eng
license: https://creativecommons.org/licenses/by/4.0/
main_file_link:
- open_access: '1'
  url: https:/​/​doi.org/​10.33232/​001c.156033
month: '01'
oa: 1
oa_version: Published Version
project:
- _id: bd9b2118-d553-11ed-ba76-db24564edfea
  grant_number: '101076224'
  name: Young galaxies as tracers and agents of cosmic reionization
publication: The Open Journal of Astrophysics
publication_identifier:
  eissn:
  - 2565-6120
publication_status: published
publisher: Maynooth Academic Publishing
quality_controlled: '1'
scopus_import: '1'
status: public
title: 'A cosmic miracle: A remarkably luminous galaxy at zspec = 14.44 confirmed
  with JWST'
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: 9
year: '2026'
...
---
OA_place: publisher
OA_type: diamond
PlanS_conform: '1'
_id: '20192'
abstract:
- lang: eng
  text: We study the physical origin and spectroscopic impact of extreme nebular emission
    in high-redshift galaxies. The nebular continuum, which can appear during an extreme
    starburst, is of particular importance as it tends to redden UV slopes and has
    a significant contribution to the UV luminosities of galaxies. Furthermore, its
    shape can be used to infer the gas density and temperature of the interstellar
    medium. First, we provide a theoretical background, showing how different stellar
    populations (SPS models, initial mass functions (IMFs), and stellar temperatures)
    and nebular conditions impact observed galaxy spectra. We demonstrate that, for
    systems with strong nebular continuum emission, 1) UV fluxes can increase by up
    to 0.7~mag (or more in the case of hot/massive stars) above the stellar continuum,
    which may help reconcile the surprising abundance of bright high-redshift galaxies
    and the elevated UV luminosity density at z>10, 2) at high gas densities, UV slopes
    can redden from \beta<-2.5 to \beta\sim-1, 3) observational measurements of \xi_{\rm
    ion} are gross underestimates, and 4) UV downturns from two-photon emission can
    masquerade as damped Ly\alpha systems. Second, we present a dataset of 58 galaxies
    observed with NIRSpec on JWST at 2.5<z<9.0 that are selected to have strong nebular
    continuum emission via the detection of the Balmer jump. Five of the 58 spectra
    are consistent with being dominated by nebular emission, exhibiting both a Balmer
    jump and a UV downturn consistent with two-photon emission. For some galaxies,
    this may imply the presence of hot massive stars and a top-heavy IMF. We conclude
    by exploring the properties of spectroscopically confirmed z>10 galaxies, finding
    that UV slopes and UV downturns are in some cases redder or steeper than expected
    from SPS models, which may hint at more exotic (e.g. hotter/more massive stars
    or AGN) ionizing sources.
acknowledgement: 'HK thanks Andrey Kravtsov for insightful comments and thoughtful
  discussions. We sincerely thank the PIs and Co-Is of the JWST programs where spectral
  data was made publicly available on the DJA. We refer interested readers to the
  following papers for survey descriptions regarding the spectral data: Bunker et
  al. (2023a); D’Eugenio et al. (2024); Bezanson et al. (2022); Barrufet et al. (2024);
  de Graaff et al. (2024); Finkelstein et al. (2024); Glazebrook et al. (2024); Pierel
  et al. (2024); Siebert et al. (2024); Maseda et al. (2024). This work is based in
  part on observations made with the NASA/ESA/CSA James Webb Space Telescope. 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 listed in Table 1. AJC and AS acknowledge funding from
  the “FirstGalaxies” Advanced Grant from the European Research Council (ERC) under
  the European Union’s Horizon 2020 research and innovation programme (Grant agreement
  No. 789056). '
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: Harley
  full_name: Katz, Harley
  last_name: Katz
- first_name: Alex J.
  full_name: Cameron, Alex J.
  last_name: Cameron
- first_name: Aayush
  full_name: Saxena, Aayush
  last_name: Saxena
- first_name: Laia
  full_name: Barrufet, Laia
  last_name: Barrufet
- first_name: Nicholas
  full_name: Choustikov, Nicholas
  last_name: Choustikov
- first_name: Nikko J.
  full_name: Cleri, Nikko J.
  last_name: Cleri
- first_name: Anna
  full_name: De Graaff, Anna
  last_name: De Graaff
- first_name: Richard S.
  full_name: Ellis, Richard S.
  last_name: Ellis
- first_name: Robert A.E.
  full_name: Fosbury, Robert A.E.
  last_name: Fosbury
- first_name: Kasper E.
  full_name: Heintz, Kasper E.
  last_name: Heintz
- first_name: Michael
  full_name: Maseda, Michael
  last_name: Maseda
- 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: Ian
  full_name: Mcconachie, Ian
  last_name: Mcconachie
- first_name: Pascal A.
  full_name: Oesch, Pascal A.
  last_name: Oesch
citation:
  ama: 'Katz H, Cameron AJ, Saxena A, et al. 21 Balmer Jump Street: The nebular continuum
    at high redshift and implications for the bright galaxy problem, UV continuum
    slopes, and early stellar populations. <i>The Open Journal of Astrophysics</i>.
    2025;8. doi:<a href="https://doi.org/10.33232/001c.142570">10.33232/001c.142570</a>'
  apa: 'Katz, H., Cameron, A. J., Saxena, A., Barrufet, L., Choustikov, N., Cleri,
    N. J., … Oesch, P. A. (2025). 21 Balmer Jump Street: The nebular continuum at
    high redshift and implications for the bright galaxy problem, UV continuum slopes,
    and early stellar populations. <i>The Open Journal of Astrophysics</i>. Maynooth
    Academic Publishing. <a href="https://doi.org/10.33232/001c.142570">https://doi.org/10.33232/001c.142570</a>'
  chicago: 'Katz, Harley, Alex J. Cameron, Aayush Saxena, Laia Barrufet, Nicholas
    Choustikov, Nikko J. Cleri, Anna De Graaff, et al. “21 Balmer Jump Street: The
    Nebular Continuum at High Redshift and Implications for the Bright Galaxy Problem,
    UV Continuum Slopes, and Early Stellar Populations.” <i>The Open Journal of Astrophysics</i>.
    Maynooth Academic Publishing, 2025. <a href="https://doi.org/10.33232/001c.142570">https://doi.org/10.33232/001c.142570</a>.'
  ieee: 'H. Katz <i>et al.</i>, “21 Balmer Jump Street: The nebular continuum at high
    redshift and implications for the bright galaxy problem, UV continuum slopes,
    and early stellar populations,” <i>The Open Journal of Astrophysics</i>, vol.
    8. Maynooth Academic Publishing, 2025.'
  ista: 'Katz H, Cameron AJ, Saxena A, Barrufet L, Choustikov N, Cleri NJ, De Graaff
    A, Ellis RS, Fosbury RAE, Heintz KE, Maseda M, Matthee JJ, Mcconachie I, Oesch
    PA. 2025. 21 Balmer Jump Street: The nebular continuum at high redshift and implications
    for the bright galaxy problem, UV continuum slopes, and early stellar populations.
    The Open Journal of Astrophysics. 8.'
  mla: 'Katz, Harley, et al. “21 Balmer Jump Street: The Nebular Continuum at High
    Redshift and Implications for the Bright Galaxy Problem, UV Continuum Slopes,
    and Early Stellar Populations.” <i>The Open Journal of Astrophysics</i>, vol.
    8, Maynooth Academic Publishing, 2025, doi:<a href="https://doi.org/10.33232/001c.142570">10.33232/001c.142570</a>.'
  short: H. Katz, A.J. Cameron, A. Saxena, L. Barrufet, N. Choustikov, N.J. Cleri,
    A. De Graaff, R.S. Ellis, R.A.E. Fosbury, K.E. Heintz, M. Maseda, J.J. Matthee,
    I. Mcconachie, P.A. Oesch, The Open Journal of Astrophysics 8 (2025).
date_created: 2025-08-17T22:01:37Z
date_published: 2025-07-25T00:00:00Z
date_updated: 2025-09-30T14:29:33Z
day: '25'
ddc:
- '520'
department:
- _id: JoMa
doi: 10.33232/001c.142570
external_id:
  arxiv:
  - '2408.03189'
file:
- access_level: open_access
  checksum: ba469d132907147f9e86d87f9124dd14
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  creator: dernst
  date_created: 2025-09-30T14:28:25Z
  date_updated: 2025-09-30T14:28:25Z
  file_id: '20412'
  file_name: 2025_OpenJourAstrophysics_Katz.pdf
  file_size: 1836432
  relation: main_file
  success: 1
file_date_updated: 2025-09-30T14:28:25Z
has_accepted_license: '1'
intvolume: '         8'
language:
- iso: eng
month: '07'
oa: 1
oa_version: Published Version
publication: The Open Journal of Astrophysics
publication_identifier:
  eissn:
  - 2565-6120
publication_status: published
publisher: Maynooth Academic Publishing
quality_controlled: '1'
scopus_import: '1'
status: public
title: '21 Balmer Jump Street: The nebular continuum at high redshift and implications
  for the bright galaxy problem, UV continuum slopes, and early stellar populations'
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: 8
year: '2025'
...