Journal Article

First Sample of Hα+O iiiλ5007 Line Emitters at z > 6 Through JWST/NIRCam Slitless Spectroscopy: Physical Properties and Line-luminosity Functions

Curti, Mirko, Jaffe, Daniel, Gennaro, Mario, Boyett, Kristan, Bunker, Andrew J, Eisenstein, Daniel J, Pirzkal, Nor, Kumari, Nimisha, Rest, Armin, Smit, Renske, Kelly, Doug, Willmer, Christopher N. A, Rieke, Marcia, Perna, Michele, Schlawin, Everett, Sunnquist, Ben, Sun, Fengwu, Baum, Stefi, Koekemoer, Anton M, Cameron, Alex J, Maiolino, Roberto, Maseda, Michael, Robertson, Brant E, Greene, Thomas P, Tacchella, Sandro, Egami, Eiichi, Boyer, Martha, Stansberry, John, Williams, Christina C

2023

Overview

We present a sample of four emission-line galaxies at z = 6.11–6.35 that were serendipitously discovered using the commissioning data for the James Webb Space Telescope (JWST)/NIRCam wide-field slitless spectroscopy mode. One of them (at z = 6.11) has been reported previously, while the others are new discoveries. These sources are selected by the secure detections of both [O iii] λ5007 and Hα lines with other fainter lines, which were tentatively detected in some cases (e.g., [O ii] λ3727, [O iii] λ4959). In the [O iii]/Hβ–[N ii]/Hα Baldwin–Phillips–Terlevich diagram, these galaxies occupy the same parameter space as that of z ∼ 2 star-forming galaxies, indicating that they have been enriched rapidly to subsolar metallicities (∼0.4 Z ⊙), similar to galaxies with comparable stellar masses at much lower redshifts. The detection of strong Hα lines suggests a higher ionizing photon production efficiency within galaxies in the early universe. We find brightening of the [O iii] λ5007 line-luminosity function (LF) from z = 3 to 6, and weak or no redshift evolution of the Hα line LF from z = 2 to 6. Both LFs are underpredicted at z ∼ 6 by a factor of ∼10 in certain cosmological simulations. This further indicates a global Lyα photon escape fraction of 7%–10% at z ∼ 6, which is slightly lower than previous estimates through the comparison of the UV-derived star formation rate density and Lyα luminosity density. Our sample recovers 66−44+128 % of z = 6.0–6.6 galaxies in the survey volume with stellar masses greater than 5 × 108 M ⊙, suggesting the ubiquity of strong Hα and [O iii] line emitters in the Epoch of Reionization, which will be further uncovered in the era of JWST.

• Publisher: IOP Publishing
• Subject: Brightening / Density / Emitters / Galaxies / H alpha line / Ionization / James Webb Space Telescope / Luminosity / Photons / Physical properties / Red shift / Space telescopes / Spectroscopy / Spectrum analysis / Star & galaxy formation / Star formation / Star formation rate