First Peek with JWST/NIRCam Wide-field Slitless Spectroscopy: Serendipitous Discovery of a Strong [O iii]/H α Emitter at z = 6.11

Fengwu Sun, Eiichi Egami, Nor Pirzkal, Marcia Rieke, Martha Boyer, Matteo Correnti, Mario Gennaro, Julien Girard, Thomas P. Greene, Doug Kelly, Anton M. Koekemoer, Jarron Leisenring, Karl Misselt, Nikolay Nikolov, Thomas L. Roellig, John Stansberry, Christina C. Williams, Christopher N.A. Willmer

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


We report the serendipitous discovery of an [O iii] λ λ4959/5007 and Hα line emitter in the Epoch of Reionization (EoR) with the James Webb Space Telescope (JWST) commissioning data taken in the NIRCam wide-field slitless spectroscopy (WFSS) mode. Located 1/455″ away from the flux calibrator P330-E, this galaxy exhibits bright [O iii] λ λ4959/5007 and Hα lines detected at 3.7σ, 9.9σ, and 5.7σ, respectively, with a spectroscopic redshift of z = 6.112 ± 0.001. The total Hβ+[O iii] equivalent width is 664 ± 98 Å (454 ± 78 Å from the [O iii] λ5007 line). This provides direct spectroscopic evidence for the presence of strong rest-frame optical lines (Hβ+[O iii] and Hα) in EoR galaxies as inferred previously from the analyses of the Spitzer/IRAC spectral energy distributions (SEDs). Two spatial and velocity components are identified in this source, possibly indicating that this system is undergoing a major merger, which might have triggered the ongoing starburst with strong nebular emission lines over a timescale of 1/42 Myr, as our SED modeling suggests. The tentative detection of He ii λ4686 line (1.9σ), if real, may indicate the existence of very young and metal-poor star-forming regions with a hard UV radiation field. Finally, this discovery demonstrates the power and readiness of the JWST/NIRCam WFSS mode, and marks the beginning of a new era for extragalactic astronomy, in which EoR galaxies can be routinely discovered via blind slitless spectroscopy through the detection of rest-frame optical emission lines.

Original languageEnglish (US)
Article numberL8
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Sep 1 2022

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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