Unveiling Luminous Lyα Emitters at z ≈ 6 through JWST/NIRCam Imaging in the COSMOS Field

Abstract

We study a sample of 14 spectroscopically confirmed Lyα emitters (LAEs) in the late era of reionization (at redshift z ≈ 6) based on the JWST/NIRCam imaging data set. These LAEs with high Lyα luminosity of L(Lyα) ∼1042.4–1043.4 erg s−1 have been covered by the (ongoing) COSMOS-Web survey over 0.28 deg2 in four NIRCam bands (F115W, F150W, F277W, and F444W). With JWST/NIRCam imaging, we determine the UV continua with M UV ranging from −20.5 to −18.5 mag. The UV slopes have a median value of β ≈ −2.35, and the steepest slopes can reach β < −3. Under the excellent spatial resolution of JWST, we identify three objects in the sample as potential merging/interacting systems. The 14 LAEs (and their components) are compact in morphology, residing substantially below the mass–size relation of high-z galaxies. We further investigate their physical properties, including the stellar mass (M *) and star formation rates (SFRs). Most of the LAEs lie on the SFR–M * main-sequence relation, while two of them, featured as “little red dots,” likely host active galactic nuclei (AGNs), implying a ∼10% AGN fraction. Moreover, we reveal that a new correlation may exist between Lyα equivalent width and the offset between Lyα and UV emission (Δd Lyα ), with a median Δd Lyα ∼ 1 kpc. This could be explained by the Lyα radiative transfer process in both the interstellar medium and circumgalactic medium. The results usher in a new era of detailed analysis on high-z LAEs with the JWST capability.