We report the discovery of a remarkable Lyα emitting galaxy at z = 7. 2782, JADES-GS-z7-LA, with EW₀ (Lyα) = 388. 0 88. 8Åand UV magnitude -17. 0. The spectroscopic redshift is confirmed via rest-frame optical lines O II, Hβ and O III in its JWST/NIRSpec Micro-Shutter Assembly (MSA) spectrum. The Lyα line is detected in both lower resolution PRISM as well as medium resolution G140M grating spectra. The LSF-deconvolved Lyα FWHM in the grating is 383. 9 56. 2 km/s and the Lyα velocity offset compared to the systemic redshift is 113. 3 80. 0 km/s, indicative of very little neutral gas or dust within the galaxy. We estimate the Lyα escape fraction to be >70%. JADES-GS-z7-LA has a O32 ratio of 11. 1 2. 2 and a R23 ratio of 11. 2 2. 6, consistent with low metallicity and high ionization parameters. Deep NIRCam imaging also revealed a close companion source (separated by 0. 23"), which exhibits similar photometry to that of JADES-GS-z7-LA, with a photometric excess in the F410M NIRCam image consistent with O III+Hβ emission at the same redshift. The spectral energy distribution of JADES-GS-z7-LA indicates a "bursty" star formation history, with a low stellar mass of 10⁷ M_. Assuming that the Lyα transmission through the intergalactic medium is the same as its measured escape fraction, an ionized region of size > 1. 5 pMpc is needed to explain the high Lyα EW and low velocity offset compared to systemic seen in JADES-GS-z7-LA. Owing to its UV-faintness, we show that it is incapable of single-handedly ionizing a region large enough to explain its Lyα emission. Therefore, we suggest that JADES-GS-z7-LA (and possibly the companion source) may be a part of a larger overdensity, presenting direct evidence of overlapping ionized bubbles at z>7.
Saxena et al. (Fri,) studied this question.