PRISMS/U13151. A Glimpse into the Earliest Phases of Galaxy Formation through an Ultra-Faint System $\approx$ 500 Myr after the Big Bang
Year: 2026
Type: preprint
Abstract: Detailed UV-to-optical studies of galaxies at z >= 10 have largely focused on bright systems (MUV <= -20 mag), leaving intrinsically faint galaxies virtually unexplored to date. Combining NIRCam, NIRSpec, and MIRI imaging and spectroscopy, we investigate UNCOVER-ABELL2744-13151 (U13151), an ultra-faint galaxy at z = 9.7995 (MUV = -17.44 mag), magnified by Abell 2744 ($μ$ = 12.8). U13151 is very blue ($β$ ~ -2.64), ultra-low mass (log10(M*/Msun) ~ 6.68), young (~ 5.5 Myr), metal-poor (Z ~ 3-6% Zsun), and compact (Re ~ 122 pc). It exhibits negligible dust attenuation, extreme ionization conditions, and intense star formation (sSFR(Ha) ~ 94 Gyr-1, or equivalently M*/SFR(Ha) ~ 10.6 Myr). Despite similarities with much brighter galaxies, its low C/O, approximately solar Ne/O, and undetected nitrogen emission suggest enrichment dominated by core-collapse supernovae, in stark contrast with similar nitrogen-enhanced systems. U13151 might be undergoing its first major episode of star formation, assembling most (if not all) of its M* through five unresolved clumps. Its high ionizing photon production efficiency (log10($ξ_{\rm ion}$/ (Hz erg-1)) ~ 25.64) suggests, through a simple toy model, suggests, through a simple toy model, that similarly short-lived episodes could contribute significantly to the ionizing photon budget of low-mass galaxies during Cosmic Reionization. We explore different evolutionary scenarios, from U13151-like galaxies potentially representing the progenitors of Blue Monsters at higher redshifts to the possibility that such systems could be the early building blocks of present-day Milky Way-like galaxies. Our results highlight the fundamental role of MIRI in studying galaxies in the early Universe and the urgent need to investigate the faintest, lowest-mass systems to shed light on the fundamental physics driving the earliest phases of galaxy formation.
Source: arXiv (Cornell University)
Authors: Rinaldi, Pierluigi, Álvarez-Márquez, Javier, Gómez, Alejandro Crespo, Colina, Luis, Carniani, Stefano, Kendrew, Sarah, Iani, Edoardo, Adamo, Angela, Abdurro'uf, Annunziatella, Marianna, Alberts, Stacey, Boogaard, Leindert A., Caputi, Karina I., Castellano, Marco, Catone, Michele, Marques-Chaves, Rui, Cooper, Ryan, Fujimoto, Seiji, Hamed, Mahmoud, Harikane, Yuichi, Harish, Santosh, Hashimoto, Takuya, Helton, Jakob M., Hsiao, Tiger Y. -Y., Kokorev, Vasily, Labiano, Álvaro, Melinder, Jens, Mitsuhashi, Ikki, Östlin, Göran, Napolitano, Lorenzo, Pérez-Díaz, Borja, Pérez-González, Pablo G., Jiménez, Carlota Prieto, Rodighiero, Giulia, Santini, Paola, Varo-O'Ferrall, Ana, Zavala, Jorge A., Zhu, Yongda
Institutions: Centro de Astrobiología, Space Telescope Science Institute, Scuola Normale Superiore, European Space Agency, Institute of Science and Technology Austria, Stockholm University, Indiana University Bloomington, AlbaNova, Indiana University, Leiden University, Leiden Observatory, University of Groningen, Astronomical Observatory of Rome, National Institute for Astrophysics, University of Padua, Osservatorio Astronomico di Padova, University of Geneva, University of Toronto, Institute for Cosmic Ray Research, The University of Tokyo, University of Tsukuba, Tomonaga Center for the History of the Universe, University of Tsukuba, Pennsylvania State University, The University of Texas at Austin, European Space Astronomy Centre, University of Colorado Boulder, Universidad Complutense de Madrid, University of Arizona, University of Massachusetts Amherst
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7223061713