The nature of an ultra-faint galaxy in the cosmic dark ages seen with JWST

Guido Roberts-Borsani, Tommaso Treu, Wenlei Chen, Takahiro Morishita, Eros Vanzella, Adi Zitrin, Pietro Bergamini, Marco Castellano, Adriano Fontana, Karl Glazebrook, Claudio Grillo, Patrick L. Kelly, Emiliano Merlin, Themiya Nanayakkara, Diego Paris, Piero Rosati, Lilan Yang, Ana Acebron, Andrea Bonchi, Kit BoyettMaruša Bradač, Gabriel Brammer, Tom Broadhurst, Antonello Calabró, Jose M. Diego, Alan Dressler, Lukas J. Furtak, Alexei V. Filippenko, Alaina Henry, Anton M. Koekemoer, Nicha Leethochawalit, Matthew A. Malkan, Charlotte Mason, Amata Mercurio, Benjamin Metha, Laura Pentericci, Justin Pierel, Steven Rieck, Namrata Roy, Paola Santini, Victoria Strait, Robert Strausbaugh, Michele Trenti, Benedetta Vulcani, Lifan Wang, Xin Wang, Rogier A. Windhorst

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


In the first billion years after the Big Bang, sources of ultraviolet (UV) photons are believed to have ionized intergalactic hydrogen, rendering the Universe transparent to UV radiation. Galaxies brighter than the characteristic luminosity L* (refs. 1,2) do not provide enough ionizing photons to drive this cosmic reionization. Fainter galaxies are thought to dominate the photon budget; however, they are surrounded by neutral gas that prevents the escape of the Lyman-α photons, which has been the dominant way to identify them so far. JD1 was previously identified as a triply-imaged galaxy with a magnification factor of 13 provided by the foreground cluster Abell 2744 (ref. 3), and a photometric redshift of z ≈ 10. Here we report the spectroscopic confirmation of this very low luminosity (≈0.05 L*) galaxy at z = 9.79, observed 480 Myr after the Big Bang, by means of the identification of the Lyman break and redward continuum, as well as multiple ≳4σ emission lines, with the Near-InfraRed Spectrograph (NIRSpec) and Near-InfraRed Camera (NIRCam) instruments. The combination of the James Webb Space Telescope (JWST) and gravitational lensing shows that this ultra-faint galaxy (M UV = −17.35)—with a luminosity typical of the sources responsible for cosmic reionization—has a compact (≈150 pc) and complex morphology, low stellar mass (107.19 M ) and subsolar (≈0.6 Z ) gas-phase metallicity.

Original languageEnglish
Pages (from-to)480-483
Number of pages4
Issue number7965
StatePublished - 17 May 2023

ASJC Scopus subject areas

  • General


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