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

September 2022 • 2022ApJ...936L...8S

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

Abstract • 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 ~55″ 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 ~2 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.

Links

• PREPRINT http://arxiv.org/abs/2207.11259
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2022ApJ...936L...8S
• ELECTR https://doi.org/10.3847/2041-8213/ac8938
• SIMBAD https://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2022ApJ...936L...8S
• PDF https://iopscience.iop.org/article/10.3847/2041-8213/ac8938/pdf
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2022ApJ...936L...8S