The JWST Emission Line Survey (JELS): The sizes and merger fraction of star-forming galaxies during the Epoch of Reionization 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 compared 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. 544 2 1412-1431 1412-1431 Oxford University Press application/pdf