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CEERS spectroscopic confirmation of NIRCam-selected z âł 8 galaxy candidates with JWST/NIRSpec: initial characterization of their properties
We present JWST NIRSpec spectroscopy for 11 galaxy candidates with photometric redshifts of z â 9 â 13 and M UV â [ â21, â18] newly identified in NIRCam images in the Cosmic Evolution Early Release Science Survey. We confirm emission line redshifts for 7 galaxies at z = 7.762-8.998 using spectra at âŒ1-5 ÎŒm either with the NIRSpec prism or its three medium-resolution (R ⌠1000) gratings. For z â 9 photometric candidates, we achieve a high confirmation rate of â90%, 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 HÎČ lines would be redshifted beyond the wavelength range observed by NIRSpec, and the Lyα continuum break is not detected with the sensitivity of the current data. Compared with Hubble Space Telescope-selected bright galaxies (M UV â â22) that are similarly spectroscopically confirmed at z â 8 â 9, these NIRCam-selected galaxies are characterized by lower star formation rates (SFRs; SFR â 4 M â yrâ1) and lower stellar masses (â108 M â), but with higher specific SFR (â40 Gyrâ1), higher [O iii]+HÎČ equivalent widths (â1100 Ă
), and elevated production efficiency of ionizing photons ( log ( Ο ion / Hz erg â 1 ) â 25.8 ) induced by young stellar populations (</p
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CEERS key paper. I. An early look into the first 500 Myr of galaxy formation with JWST
We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z ~ 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin2, to search for candidate galaxies at z > 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at z ~ 9-16. These objects are compact with a median half-light radius of ~0.5 kpc. We present an early estimate of the z ~ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at M UV ~ -20 appears to evolve very little from z ~ 9 to 11. We also find that the abundance (surface density [arcmin-2]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z > 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultrahigh-redshift galaxies with which to further explore these conclusions.</p
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CEERS key paper. IV. A triality in the nature of HST-dark galaxies
The new capabilities that JWST offers in the near- and mid-infrared (IR) are used to investigate in unprecedented detail the nature of optical/near-IR-faint, mid-IR-bright sources, with HST-dark galaxies among them. We gather JWST data from the CEERS survey in the Extended Groth Strip, jointly with HST data, and analyze spatially resolved optical-to-mid-IR spectral energy distributions to estimate photometric redshifts in two dimensions and stellar population properties on a pixel-by-pixel basis for red galaxies detected by NIRCam. We select 138 galaxies with F150W - F356W > 1.5 mag and F356W 100 Gyr-1); (2) 18% are quiescent/dormant (i.e., subject to reignition/rejuvenation) galaxies (QGs) at 3 < z < 5, with log M ? / M ? ~ 10 and poststarburst mass-weighted ages (0.5-1.0 Gyr); and (3) 11% are strong young starbursts with indications of high equivalent width emission lines (typically, [O iii]+HĂ) at 6 < z < 7 (XELG-z6) and log M ? / M ? ~ 9.5 . The sample is dominated by disk-like galaxies with remarkable compactness for XELG-z6 (effective radii smaller than 0.4 kpc). Large attenuations in SFGs, 2 < A(V) < 5 mag, are found within 1.5 times the effective radius, approximately 2 kpc, while QGs present A(V) ~ 0.2 mag. Our SED-fitting technique reproduces the expected dust emission luminosities of IR-bright and submillimeter galaxies. This study implies high levels of star formation activity between z ~ 20 and z ~ 10, where virtually 100% of our galaxies had already formed 108 M ?, 60% had assembled 109 M ?, and 10% up to 1010 M ? (in situ or ex situ)