Spectroscopic Confirmation of CEERS NIRCam-selected Galaxies at z ≃ 8–10

Abstract

We present JWST/NIRSpec prism spectroscopy of seven galaxies selected from Cosmic Evolution Early Release Science (CEERS) survey NIRCam imaging with photometric redshifts z phot > 8. We measure emission line redshifts of z = 7.65 and 8.64 for two galaxies. For two other sources without securely detected emission lines we measure z = 9.77 − 0.29 + 0.37 and 10.01 − 0.19 + 0.14 by fitting model spectral templates to the prism data, from which we detect continuum breaks consistent with Lyα opacity from a mostly neutral intergalactic medium. The presence of strong breaks and the absence of strong emission lines give high confidence that these two galaxies have redshifts z > 9.6, but the redshift values derived from the breaks alone have large uncertainties given the low spectral resolution and relatively low S/N of the CEERS NIRSpec prism data. The two z ∼ 10 sources observed are relatively luminous (M UV < −20), with blue continua (−2.3 ≲ β ≲ −1.9) and low dust attenuation ( A V ≃ 0.15 − 0.1 + 0.3 ); and at least one of them has a high stellar mass for a galaxy at that redshift ( log ( M ⋆ / M ⊙ ) ≃ 9.3 − 0.3 + 0.2 ). Considered together with spectroscopic observations of other CEERS NIRCam-selected high-z galaxy candidates in the literature, we find a high rate of redshift confirmation and low rate of confirmed interlopers (8%). Ten out of 35 z > 8 candidates with CEERS NIRSpec spectroscopy do not have secure redshifts, but the absence of emission lines in their spectra is consistent with redshifts z > 9.6. We find that z > 8 photometric redshifts are generally in agreement (within their uncertainties) with the spectroscopic values, but also that the photometric redshifts tend to be slightly overestimated (〈Δz〉 = 0.45 ± 0.11), suggesting that current templates do not fully describe the spectra of very-high-z sources. Overall, the spectroscopy solidifies photometric redshift evidence for a high spatial density of bright galaxies at z > 8 compared to theoretical model predictions, and further disfavors an accelerated decline in the integrated UV luminosity density at z > 8.

Strong asymptotic giant branch stars’ spectral features in distant quiescent galaxies: Impact on galaxy evolution

“…The z > 1 limit imposed on the sample ensures that the age-sensitive spectral region around rest-frame 4000 Å break is covered by JWST/NIRSpec with good sensitivity. We cross-matched these phometricallyselected candidates with the 1491 galaxies with secure spectroscopic redshift observed with JWST/NIRSpec during the Cosmic Evolution Early Release Science (CEERS) program 26,27 and during a subsequent NIRSpec follow-up program (DD-2750) 28 . This resulted in a spectroscopic sample of 31 galaxies, for which we visually inspected the spectra.…”

“…The NIRSpec data processing followed the same methodology as used for other CEERS NIRSpec observations 27,28,[57][58][59] . The NIRSpec data reduction was based on the STScI Calibration Pipeline 60 version 1.8.5 and the Calibration Reference Data System (CRDS) mapping 1041 for objects 8595 and 9025, and CRDS mapping 1029 for D36123.…”

“…The flux error for the extracted spectra was calculated by the JWST pipeline using an instrumental noise. We rescaled all flux errors multiplying by a factor of ∼1.5 to account for correlations induced by the pipeline 27 . The spectrum of 9025, observed with 3 mediumresolution gratings, was calibrated through several steps.…”