A Census of the Bright z = 8.5–11 Universe with the Hubble and Spitzer Space Telescopes in the CANDELS Fields

Abstract

We present the results from a new search for candidate galaxies at z ≈ 8.5–11 discovered over the 850 arcmin2 area probed by the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS). We use a photometric-redshift selection including both Hubble and Spitzer Space Telescope photometry to robustly identify galaxies in this epoch at H 160 < 26.6. We use a detailed vetting procedure, including screening against persistence and stellar contamination, and the inclusion of ground-based imaging and follow-up Hubble Space Telescope imaging to build a robust sample of 11 candidate galaxies, three presented here for the first time. The inclusion of Spitzer/IRAC photometry in the selection process reduces contamination, and yields more robust redshift estimates than Hubble alone. We constrain the evolution of the rest-frame ultraviolet luminosity function via a new method of calculating the observed number densities without choosing a prior magnitude bin size. We find that the abundance at our brightest probed luminosities (M UV = − 22.3) is consistent with predictions from simulations that assume that galaxies in this epoch have gas depletion times at least as short as those in nearby starburst galaxies. Due to large Poisson and cosmic variance uncertainties, we cannot conclusively rule out either a smooth evolution of the luminosity function continued from z = 4–8, or an accelerated decline at z > 8. We calculate that the presence of seven galaxies in a single field Extended Groth Strip is an outlier at the 2σ significance level, implying the discovery of a significant over-density. These scenarios will be imminently testable to high confidence within the first year of observations of the James Webb Space Telescope.

Searching for Islands of Reionization: A Potential Ionized Bubble Powered by a Spectroscopic Overdensity at z = 8.7

“…We obtained Keck/MOSFIRE J-band spectroscopic followup targeting Lyα from a sample of candidate z = 9-10 galaxies recently published by Finkelstein et al (2022), discovered in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS; Grogin et al 2011;Koekemoer et al 2011). The full details of their selection are discussed in Finkelstein et al (2022), but, in brief, these galaxies were selected as those with significant (>7σ) photometric detections, with photometric redshifts that were strongly constrained to be at z > 8.…”

“…We obtained Keck/MOSFIRE J-band spectroscopic followup targeting Lyα from a sample of candidate z = 9-10 galaxies recently published by Finkelstein et al (2022), discovered in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS; Grogin et al 2011;Koekemoer et al 2011). The full details of their selection are discussed in Finkelstein et al (2022), but, in brief, these galaxies were selected as those with significant (>7σ) photometric detections, with photometric redshifts that were strongly constrained to be at z > 8. Finkelstein et al (2022) detailed several vetting procedures done to ensure the robustness of the sample, culminating in a sample of 14 initial z = 9-10 candidates, which were honed to 11 robust candidates following the inclusion of ground-based imaging and additional Hubble Space Telescope (HST) F098M and F140W imaging to rule out low-redshift solutions.…”

“…The full details of their selection are discussed in Finkelstein et al (2022), but, in brief, these galaxies were selected as those with significant (>7σ) photometric detections, with photometric redshifts that were strongly constrained to be at z > 8. Finkelstein et al (2022) detailed several vetting procedures done to ensure the robustness of the sample, culminating in a sample of 14 initial z = 9-10 candidates, which were honed to 11 robust candidates following the inclusion of ground-based imaging and additional Hubble Space Telescope (HST) F098M and F140W imaging to rule out low-redshift solutions. Figure 1 shows the apparent magnitude distribution of the final sample of galaxies in this survey.…”

“…The details of the observations are described in Table 1. We observed 9 of the 11 galaxies from the final sample of Finkelstein et al (2022) with this program (which also includes several sources previously published by Oesch et al 2018;Bouwens et al 2019). Of the two sources not observed, we explicitly avoided EGS_z910_6811, 14 as this is EGSY8p7 from Zitrin et al (2015) and already has a spectroscopic redshift from Lyα at z = 8.683 from MOSFIRE, while source EGS_z910_68560 lies far from the other targeted sources and would have required its own pointing.…”

“…Of the two sources not observed, we explicitly avoided EGS_z910_6811, 14 as this is EGSY8p7 from Zitrin et al (2015) and already has a spectroscopic redshift from Lyα at z = 8.683 from MOSFIRE, while source EGS_z910_68560 lies far from the other targeted sources and would have required its own pointing. We list the observed galaxies in Table 2, including the three candidates that Finkelstein et al (2022) removed from their final sample owing to additional imaging obtained that pushed the photometric redshift calculations to lower redshifts, but which we still observed here (see the Appendix).…”