---
DOAJ_listed: '1'
OA_place: publisher
OA_type: gold
PlanS_conform: '1'
_id: '20660'
abstract:
- lang: eng
  text: "We used observations from the JWST Emission Line Survey (JELS) to measure
    the half-light radii (re) of 23 Hα-emitting starforming (SF) galaxies at z = 6.1
    in the PRIMER/COSMOS field. Galaxy sizes were measured in JWST near-infrared camera
    observations in rest-frame Hα (tracing recent star formation) with the F466N and
    F470N narrow-band filters from JELS, and\r\ncompared against rest-R- and V -band
    (tracing established stellar populations) and near-ultraviolet sizes. We find
    a size–stellar mass(re − M∗) relationship with a slope that is consistent with
    literature values at lower redshifts, though offset to lowersizes. We observe
    a large scatter in re at low stellar mass (M∗ < 10^8.4 Mo) which we believe is
    the result of bursty star formation histories (SFHs) of SF galaxies at the Epoch
    of Reionization (EoR). We find that the stellar and ionized gas components are
    similar in size at z = 6.1. The evidence of already-established stellar components
    in these Hα emitters (HAEs) indicates previous episodes of star formation have
    occurred. As such, following other JELS studies finding our HAEs are undergoing
    a current burst of star formation, we believe our results indicate that SF galaxies
    at the end of the EoR have already experienced a bursty SFH. From our re − M∗
    relationship, we find re,F444W = 0.76 ± 0.46 kpc for fixed stellar mass M∗ = 10^9.25
    M, which is in agreement with other observations and simulations of SF galaxies
    in the literature. We find a close-pair (major) merger fraction of (fmaj. merger
    =0.44 ± 0.22) fmerger = 0.43 ± 0.11 for galaxy separations d <~ 25 kpc, which
    is in agreement with other z ≈ 6 studies."
acknowledgement: "This work makes use of ASTROPY, 7 a community-developed core PYTHON
  package for Astronomy (Astropy Collaboration 2013, 2018, 2022), as well as the NUMPY
  (C. R. Harris et al. 2020) and SCIPY (P.Virtanen et al. 2020) packages(see also
  T. E. Oliphant 2007). All plots\r\nwere created using the MATPLOTLIB 2D graphics
  PYTHON package (J. D. Hunter 2007). Conversions between redshift and lookback time
  in our selected cosmological model were done using the Javascript cosmological calculator
  from E. L. Wright (2006).8 The authors would like to thank the anonymous referee
  for their constructive comments and suggestions which have strengthened the analysis
  of this work and improved the paper. The authors also gratefully acknowledge Ian
  Smail for providing valuable feedback and helping to guide the science of this paper.
  This work is based on observations made with the NASA/ESA/CSA James Webb Space\r\nTelescope.
  The data were obtained from the Mikulski Archive for Space Telescopes9 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 no. 2321 (JELS) and GO no. 1837 (PRIMER).
  The authors acknowledge the PRIMER team for developing their observing program with
  a zero-exclusive-access period. HMOS acknowledges support from an STFC PhD studentship
  and the Faculty of Science and Technology at Lancaster University. PNB is grateful
  for support from the UK STFC\r\nvia grants ST/V000594/1 and ST/Y000951/1. JSD acknowledges
  the support of the Royal Society via a Royal Society Research Professorship. LOF
  acknowledges funding by ANID BECAS/DOCTORADO NACIONAL 21220499.CLH acknowledges
  support from the Oxford\r\nHintze Centre for Astrophysical Surveys which is funded
  through generous support from the Hintze family charity foundation. EI gratefully
  acknowledge financial support from ANID – MILENIO –NCN2024 112 and ANID FONDECYT
  Regular 1221846. For the purpose of open access, the authors have applied a Creative
  Commons attribution (CC BY) licence to any author accepted manuscript version arising."
article_processing_charge: Yes
article_type: original
author:
- first_name: H. M.O.
  full_name: Stephenson, H. M.O.
  last_name: Stephenson
- first_name: J. P.
  full_name: Stott, J. P.
  last_name: Stott
- first_name: C. A.
  full_name: Pirie, C. A.
  last_name: Pirie
- first_name: K. J.
  full_name: Duncan, K. J.
  last_name: Duncan
- first_name: D. J.
  full_name: Mcleod, D. J.
  last_name: Mcleod
- first_name: P. N.
  full_name: Best, P. N.
  last_name: Best
- first_name: M.
  full_name: Brinch, M.
  last_name: Brinch
- first_name: M.
  full_name: Clausen, M.
  last_name: Clausen
- first_name: R. K.
  full_name: Cochrane, R. K.
  last_name: Cochrane
- first_name: J. S.
  full_name: Dunlop, J. S.
  last_name: Dunlop
- first_name: S. R.
  full_name: Flury, S. R.
  last_name: Flury
- first_name: J. E.
  full_name: Geach, J. E.
  last_name: Geach
- first_name: C. L.
  full_name: Hale, C. L.
  last_name: Hale
- first_name: E.
  full_name: Ibar, E.
  last_name: Ibar
- first_name: Zefeng
  full_name: Li, Zefeng
  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: R. J.
  full_name: Mclure, R. J.
  last_name: Mclure
- first_name: L.
  full_name: Ossa-Fuentes, L.
  last_name: Ossa-Fuentes
- first_name: A. L.
  full_name: Patrick, A. L.
  last_name: Patrick
- first_name: D.
  full_name: Sobral, D.
  last_name: Sobral
- first_name: A. M.
  full_name: Swinbank, A. M.
  last_name: Swinbank
citation:
  ama: 'Stephenson HMO, Stott JP, Pirie CA, et al. The JWST Emission Line Survey (JELS):
    The sizes and merger fraction of star-forming galaxies during the Epoch of Reionization.
    <i>Monthly Notices of the Royal Astronomical Society</i>. 2025;544(2):1412-1431.
    doi:<a href="https://doi.org/10.1093/mnras/staf1725">10.1093/mnras/staf1725</a>'
  apa: 'Stephenson, H. M. O., Stott, J. P., Pirie, C. A., Duncan, K. J., Mcleod, D.
    J., Best, P. N., … Swinbank, A. M. (2025). The JWST Emission Line Survey (JELS):
    The sizes and merger fraction of star-forming galaxies during the Epoch of Reionization.
    <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press.
    <a href="https://doi.org/10.1093/mnras/staf1725">https://doi.org/10.1093/mnras/staf1725</a>'
  chicago: 'Stephenson, H. M.O., J. P. Stott, C. A. Pirie, K. J. Duncan, D. J. Mcleod,
    P. N. Best, M. Brinch, et al. “The JWST Emission Line Survey (JELS): The Sizes
    and Merger Fraction of Star-Forming Galaxies during the Epoch of Reionization.”
    <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press,
    2025. <a href="https://doi.org/10.1093/mnras/staf1725">https://doi.org/10.1093/mnras/staf1725</a>.'
  ieee: 'H. M. O. Stephenson <i>et al.</i>, “The JWST Emission Line Survey (JELS):
    The sizes and merger fraction of star-forming galaxies during the Epoch of Reionization,”
    <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 544, no. 2. Oxford
    University Press, pp. 1412–1431, 2025.'
  ista: 'Stephenson HMO, Stott JP, Pirie CA, Duncan KJ, Mcleod DJ, Best PN, Brinch
    M, Clausen M, Cochrane RK, Dunlop JS, Flury SR, Geach JE, Hale CL, Ibar E, Li
    Z, Matthee JJ, Mclure RJ, Ossa-Fuentes L, Patrick AL, Sobral D, Swinbank AM. 2025.
    The JWST Emission Line Survey (JELS): The sizes and merger fraction of star-forming
    galaxies during the Epoch of Reionization. Monthly Notices of the Royal Astronomical
    Society. 544(2), 1412–1431.'
  mla: 'Stephenson, H. M. O., et al. “The JWST Emission Line Survey (JELS): The Sizes
    and Merger Fraction of Star-Forming Galaxies during the Epoch of Reionization.”
    <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 544, no. 2, Oxford
    University Press, 2025, pp. 1412–31, doi:<a href="https://doi.org/10.1093/mnras/staf1725">10.1093/mnras/staf1725</a>.'
  short: H.M.O. Stephenson, J.P. Stott, C.A. Pirie, K.J. Duncan, D.J. Mcleod, P.N.
    Best, M. Brinch, M. Clausen, R.K. Cochrane, J.S. Dunlop, S.R. Flury, J.E. Geach,
    C.L. Hale, E. Ibar, Z. Li, J.J. Matthee, R.J. Mclure, L. Ossa-Fuentes, A.L. Patrick,
    D. Sobral, A.M. Swinbank, Monthly Notices of the Royal Astronomical Society 544
    (2025) 1412–1431.
date_created: 2025-11-23T23:01:37Z
date_published: 2025-12-01T00:00:00Z
date_updated: 2025-12-01T15:25:11Z
day: '01'
ddc:
- '520'
department:
- _id: JoMa
doi: 10.1093/mnras/staf1725
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oa_version: Published Version
page: 1412-1431
publication: Monthly Notices of the Royal Astronomical Society
publication_identifier:
  eissn:
  - 1365-2966
  issn:
  - 0035-8711
publication_status: published
publisher: Oxford University Press
quality_controlled: '1'
scopus_import: '1'
status: public
title: 'The JWST Emission Line Survey (JELS): The sizes and merger fraction of star-forming
  galaxies during the Epoch of Reionization'
tmp:
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  legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
  name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
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