JADES: Discovery of extremely high equivalent width Lyman-alpha emission from a faint galaxy within an ionized bubble at z=7.3
Creators: name: Saxena, Aayush
name: Robertson, Brant E.
name: Bunker, Andrew J.
name: Endsley, Ryan
name: Cameron, Alex J.
name: Charlot, Stephane
name: Simmonds, Charlotte
name: Tacchella, Sandro
name: Witstok, Joris
name: Willott, Chris
name: Carniani, Stefano
name: Curtis-Lake, Emma
name: Ferruit, Pierre
name: Jakobsen, Peter
name: Arribas, Santiago
name: Chevallard, Jacopo
name: Curti, Mirko
name: D'Eugenio, Francesco
name: De Graaff, Anna
name: Jones, Gareth C.
name: Looser, Tobias J.
name: Maseda, Michael V.
name: Rawle, Tim
name: Rix, Hans-Walter
name: Del Pino, Bruno Rodríguez
name: Smit, Renske
name: Übler, Hannah
name: Eisenstein, Daniel J.
name: Hainline, Kevin
name: Hausen, Ryan
name: Johnson, Benjamin D.
name: Rieke, Marcia
name: Williams, Christina C.
name: Willmer, Christopher N. A.
name: Baker, William M.
name: Bhatawdekar, Rachana
name: Bowler, Rebecca
name: Boyett, Kristan
name: Chen, Zuyi
name: Egami, Eiichi
name: Ji, Zhiyuan
name: Nelson, Erica
name: Perna, Michele
name: Sandles, Lester
name: Scholtz, Jan
name: Shivaei, Irene
Publisher: name: arXiv
Year: 2023
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We report the discovery of a remarkable Ly$α$ emitting galaxy at z = 7.2782, JADES-GS-z7-LA, with EW$_0$(Ly$α$) $= 388.0 \pm 88.8$Åand UV magnitude -17.0. The spectroscopic redshift is confirmed via rest-frame optical lines [O II], H$β$ and [O III] in its JWST/NIRSpec Micro-Shutter Assembly (MSA) spectrum. The Ly$α$ line is detected in both lower resolution PRISM as well as medium resolution G140M grating spectra. The LSF-deconvolved Ly$α$ FWHM in the grating is $383.9 \pm 56.2$ km/s and the Ly$α$ velocity offset compared to the systemic redshift is $113.3 \pm 80.0$ km/s, indicative of very little neutral gas or dust within the galaxy. We estimate the Ly$α$ escape fraction to be &gt;70%. JADES-GS-z7-LA has a O32 ratio of $11.1 \pm 2.2$ and a R23 ratio of $11.2 \pm 2.6$, 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]+H$β$ 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 $\approx 10^7$ $M_\odot$. Assuming that the Ly$α$ transmission through the intergalactic medium is the same as its measured escape fraction, an ionized region of size &gt; 1.5 pMpc is needed to explain the high Ly$α$ 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 Ly$α$ 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 $z&gt;7$.
description: 14 pages, 8 figures, Accepted for publication in A&amp;A