Document Type

Article

Publication Title

Astrophysical Journal Letters

Department

Physics

ISSN

20418213

Volume

940

Issue

2

DOI

10.3847/2041-8213/ac966e

First Page

1

Last Page

15

Publication Date

12-1-2022

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 zphot = 11.8-0.2+0.3 (1σ uncertainty) with mF200W = 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 (rh = 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.

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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