James Webb Space Telescope Feed Post


Literature
Date: 10/8/2023

Harvard ADS: JADES: Discovery of extremely high equivalent width Lyman-α emission from a faint galaxy within an ionized bubble at z = 7.3

Paper abstract: We report the discovery of a remarkable Lya emitting galaxy at z = 7.2782, JADES-GS+53.16746-27.7720 (shortened to JADES-GS-z7-LA), with rest-frame equivalent width, EW0(Lya) = 388.0 ± 88.8 Å and UV magnitude -17.0. The spectroscopic redshift is confirmed via rest-frame optical lines [O II], Hß and [O III] in its JWST/NIRSpec Micro-Shutter Assembly (MSA) spectrum. The Lya line is detected in both lower resolution (R ~ 100) PRISM as well as medium resolution (R ~ 1000) G140M grating spectra. The line spread function-deconvolved Lya full width at half maximum in the grating is 383.9 ± 56.2 km s-1 and the Lya velocity offset compared to the systemic redshift is 113.3 ± 80.0 km s-1, indicative of very little neutral gas or dust within the galaxy. We estimate the Lya escape fraction to be > 70%. JADES-GS-z7-LA has a [O III]/[O II] ratio (O32) of 11.1 ± 2.2 and a ([O III] + [O II])/Hß ratio (R23) 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] + Hß 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 Lya 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 Lya 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 Lya 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.