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

Aayush Saxena, Brant E. Robertson, Andrew J. Bunker, Ryan Endsley, Alex J. Cameron, Stephane Charlot, Charlotte Simmonds, Sandro Tacchella, Joris Witstok, Chris Willott, Stefano Carniani, Emma Curtis-Lake, Pierre Ferruit, Peter Jakobsen, Santiago Arribas, Jacopo Chevallard, Mirko Curti, Francesco D'Eugenio, Anna De Graaff, Gareth C. JonesTobias J. Looser, Michael V. Maseda, Tim Rawle, Hans-Walter Rix, Bruno Rodríguez Del Pino, Renske Smit, Hannah Übler, Daniel J. Eisenstein, Kevin Hainline, Ryan Hausen, Benjamin D. Johnson, Marcia Rieke, Christina C. Williams, Christopher N. A. Willmer, William M. Baker, Rachana Bhatawdekar, Rebecca Bowler, Kristan Boyett, Zuyi Chen, Eiichi Egami, Zhiyuan Ji, Nimisha Kumari, Erica Nelson, Michele Perna, Lester Sandles, Jan Scholtz, Irene Shivaei

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Abstract

We report the discovery of a remarkable Lyα emitting galaxy at z = 7.2782, JADES-GS+53.16746-27.7720 (shortened to JADES-GS-z7-LA), with rest-frame equivalent width, EW 0(Lyα) = 388.0 ± 88.8 Å and 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 (R ∼ 100) PRISM as well as medium resolution (R ∼ 1000) G140M grating spectra. The line spread function-deconvolved Lyα full width at half maximum in the grating is 383.9 ± 56.2 km s -1 and the Lyα 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 Lyα 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])/Hβ 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- ³), 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 10 7† 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.

Original languageEnglish
Article numberA68
Pages (from-to)1-13
Number of pages13
JournalAstronomy & Astrophysics
Volume678
Issue numberOctober 2023
DOIs
Publication statusPublished - 5 Oct 2023

Keywords

  • astro-ph.GA
  • astro-ph.CO
  • First stars
  • Galaxies: evolution
  • Dark ages
  • Reionization
  • Galaxies: star formation
  • Galaxies: high-redshift

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