CEERS Spectroscopic Confirmation of NIRCam-selected z 8 Galaxy Candidates with JWST/NIRSpec: Initial Characterization of Their Properties
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AbstractWe present JWST NIRSpec spectroscopy for 11 galaxy candidates with photometric redshifts of z 9 13 and MUV [ 21, 18] newly identified in NIRCam images in the Cosmic Evolution Early Release Science Survey. We confirm emission line redshifts for 7 galaxies at z = 7.7628.998 using spectra at 15 m either with the NIRSpec prism or its three medium-resolution (R 1000) gratings. For z 9 photometric candidates, we achieve a high confirmation rate of 90%, which validates the classical dropout selection from NIRCam photometry. No robust emission lines are identified in three galaxy candidates at z > 10, where the strong [O iii] and H lines would be redshifted beyond the wavelength range observed by NIRSpec, and the Ly continuum break is not detected with the sensitivity of the current data. Compared with Hubble Space Telescope-selected bright galaxies (MUV 22) that are similarly spectroscopically confirmed at z 8 9, these NIRCam-selected galaxies are characterized by lower star formation rates (SFRs; SFR 4 M yr1) and lower stellar masses (108M), but with higher specific SFR (40 Gyr1), higher [O iii]+H equivalent widths (1100 ), and elevated production efficiency of ionizing photons (log(ion/Hzerg1)25.8) induced by young stellar populations (<10 Myr) accounting for 20% of the galaxy mass, highlighting the key contribution of faint galaxies to cosmic reionization. Taking advantage of the homogeneous selection and sensitivity, we also investigate metallicity and ISM conditions with empirical calibrations using the [O iii]5008/H ratio. We find that galaxies at z 8 9 have higher SFRs and lower metallicities than galaxies at similar stellar masses at z 2 6, which is generally consistent with the current galaxy formation and evolution models.
