An Hα Impression of Lyα Galaxies at z ≃ 6 with Deep JWST/NIRCam Imaging

We present a study of seven spectroscopically confirmed (Lyα-emitting) galaxies at redshift z ≃ 6 using the JWST/NIRCam imaging data. These galaxies, with a wide range of Lyα luminosities, were recently observed in a series of NIRCam broad and medium bands. We constrain the rest-frame UV/optical continua and measure the Hα line emission of the galaxies using the combination of JWST/NIRCam and archival HST/WFC3 infrared photometry. We further estimate the escape fractions of their Lyα photons (${f}_{\mathrm{esc}}^{\mathrm{Ly}\alpha }$) and the production efficiency of ionizing photons (ξion). Among the sample, six out of seven galaxies have Lyα escape fractions of ≲10%, which might be the status for most of the star-forming galaxies at z ≃ 6. One UV-faint Lyα galaxy with an extremely blue UV slope has a large value of ${f}_{\mathrm{esc}}^{\mathrm{Ly}\alpha }$ reaching ≃50%. These galaxies have a broad range of ξion over log10 ξion,0 (Hz erg−1) ∼ 25.0–26.5. We find that UV-fainter galaxies with bluer UV-continuum slopes likely have higher escape fractions of Lyα photons. We also find that galaxies with higher Lyα line emission tend to produce ionizing photons more efficiently. The most Lyα-luminous galaxy in the sample has a very high ξion,0 of log10 ξion,0 (Hz erg−1) > 26. Our results support the scenario that Lyα galaxies may have served as an important contributor to cosmic reionization. Blue and bright Lyα galaxies are excellent targets for JWST follow-up spectroscopic observations.