Unveiling Luminous Ly$\alpha$ Emitters at $z\approx 6$ through JWST/NIRCam Imaging in the COSMOS Field

Abstract

We study a sample of 14 spectroscopically confirmed Ly$\alpha$ Emitters (LAEs) in the late era of reionization (at redshift $z\approx 6$) based on the JWST/NIRCam imaging dataset. These LAEs with high Ly$\alpha$ luminosity of $L$(Ly$\alpha$) $\sim 10^{42.4-43.4}$ erg s${}^{-1}$ have been covered by the (ongoing) COSMOS-Web survey (Kartaltepe et al. 2021; Casey et al. 2022) over $0.28$ deg${}^2$ in four NIRCam bands (F115W, F150W, F277W, and F444W). With JWST imaging, we determine the UV continua with $M_{\mathrm{UV}}$ ranging from $-20.5$ to $-18.5$ mag. The UV slopes have a median value of $\beta \approx -2.35$, and the steepest slope can reach $\beta <-3$. Under an excellent spatial resolution of JWST, we identify three out of 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 the stellar mass ($M_{\ast }$) and star-formation rates (SFRs). Most of the LAEs lie on the SFR-$M_{\ast }$ main-sequence relation while two of them featured as "little red dots" likely host active galactic nuclei (AGN), implying a $\sim 10\%$ AGN fraction. Moreover, we reveal that a new correlation may exist between Ly$\alpha$ equivalent width and the offset between Ly$\alpha$ and UV emission ($\Delta d_{\mathrm{Ly}\alpha }$) with a median $\Delta d_{\mathrm{Ly}\alpha }\sim 1$ kpc. This could be explained by Ly$\alpha$ radiative transfer process in both ISM and CGM. The results usher a new era of detailed analysis on high-$z$ LAEs with the JWST capability.

15 pages, 5 figures, accepted by ApJL

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