The <i>JWST</i> Emission Line Survey (JELS): the sizes and merger fraction of star-forming galaxies during the Epoch of Reionization

2025/09/09 by H M O Stephenson, H. M. O. Stephenson, Stephenson, H. M. O. +48 · 2 voices
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #astro-ph.GA

paper · pdf · doi:10.1093/mnras/staf1725

openalex created_date 2025/10/09 · openalex publication_date 2025/10/09 · openalex updated_date 2026/07/28

Abstract

ABSTRACT We used observations from the JWST Emission Line Survey (JELS) to measure the half-light radii (r_e) of 23 Hα-emitting star-forming (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 compared against rest-R- and V-band (tracing established stellar populations) and near-ultraviolet sizes. We find a size–stellar mass (r_e-M_*) relationship with a slope that is consistent with literature values at lower redshifts, though offset to lower sizes. We observe a large scatter in r_e at low stellar mass (M_*&amp;lt; 10^8.4 \mathrm M_\odot ) 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 r_e-M_* relationship, we find r_{e, F444W}=0.76± 0.46 kpc for fixed stellar mass M_*=10^9.25 M_\odot , which is in agreement with other observations and simulations of SF galaxies in the literature. We find a close-pair (major) merger fraction of (f_{maj. merger}=0.44± 0.22) f_merger=0.43± 0.11 for galaxy separations d\lesssim 25 kpc, which is in agreement with other z≈ 6 studies.

Citations

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Discussions

• Hello everyone! My first Bluesky posts! I am very pleased to share that my 3rd first-author paper of my PhD is now available on arXiv! The paper has also been submitted to MNRAS following minor sugges [bsky, 21 points, 1 comments]
• Here he is in viva attire - thesis title: "The Impacts of Star Formation on Galaxy Evolution since the End of Cosmic Reionization" which produced 3 first author papers arxiv.org/abs/2509.08045 arxiv.o [bsky, 4 points, 1 comments]

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