A Long Time Ago in a Galaxy Far, Far Away: A Candidate z ∼ 12 Galaxy in Early JWST CEERS Imaging

Abstract

We report the discovery of a candidate galaxy with a photo-z of z ∼ 12 in the first epoch of the James Webb Space Telescope (JWST) Cosmic Evolution Early Release Science Survey. Following conservative selection criteria, we identify a source with a robust z phot = 11.8 − 0.2 + 0.3 (1σ uncertainty) with m F200W = 27.3 and ≳7σ detections in five filters. The source is not detected at λ < 1.4 μm in deep imaging from both Hubble Space Telescope (HST) and JWST and has faint ∼3σ detections in JWST F150W and HST F160W, which signal a Lyα break near the red edge of both filters, implying z ∼ 12. This object (Maisie’s Galaxy) exhibits F115W − F200W > 1.9 mag (2σ lower limit) with a blue continuum slope, resulting in 99.6% of the photo-z probability distribution function favoring z > 11. All data-quality images show no artifacts at the candidate’s position, and independent analyses consistently find a strong preference for z > 11. Its colors are inconsistent with Galactic stars, and it is resolved (r h = 340 ± 14 pc). Maisie’s Galaxy has log M */M ⊙ ∼ 8.5 and is highly star-forming (log sSFR ∼ −8.2 yr−1), with a blue rest-UV color (β ∼ −2.5) indicating little dust, though not extremely low metallicity. While the presence of this source is in tension with most predictions, it agrees with empirical extrapolations assuming UV luminosity functions that smoothly decline with increasing redshift. Should follow-up spectroscopy validate this redshift, our universe was already aglow with galaxies less than 400 Myr after the Big Bang.

Dusty Starbursts Masquerading as Ultra-high Redshift Galaxies in JWST CEERS Observations

“…We thus conclude that a lower-redshift scenario for Maisie's galaxy in which the source is rather associated with a DSFG is unlikely. Given the lack of far-infrared-to-submillimeter detections, the best-fit SEDs and their associated redshift probability distributions for Maisie's galaxy would be similar to those reported in Finkelstein et al (2022a). Hence, to avoid duplication, they are not included in this Letter.…”

“…Here, we only use data from CEERS pointing #2, which covers all three objects we study in seven filters: F115W, F150W, F200W, F277W, F356W, F410M, and F444W. After a three-dither pattern, the total exposure time was typically 47 minutes per filter, with the exception of F115W, whose integration time is longer (see details in Finkelstein et al 2022a andS. Finkelstein 2022, in preparation).…”

Early JWST Imaging Reveals Strong Optical and NIR Color Gradients in Galaxies at z ∼ 2 Driven Mostly by Dust

“…The NIRCam imaging used in this study was taken between 2022 June 22 and 28 as part of the CEERS survey (see Finkelstein et al 2017Finkelstein et al , 2022 covering roughly 40 arcmin 2 in the AEGIS field. For this study, we focus on the three broadband filters: F115W, F200W, and F356W.…”

A Candidate for the Least-massive Black Hole in the First 1.1 Billion Years of the Universe

“…The 6.5 m space observatory is expected to be a game changer in the field of extragalactic observations. Numerous papers have claimed the first detection of ultra high-redshift galaxies at z  10, waiting for spectroscopic confirmation (e.g., Adams et al 2023;Castellano et al 2022;Donnan et al 2023;Finkelstein et al 2022aFinkelstein et al , 2022bHarikane et al 2022b;Naidu et al 2022). Likewise, the superb sensitivity of JWST may also enable us to witness rapidly accreting seed BHs far beyond the current samples of high-redshift AGNs.…”