A large overdensity of LRD-like galaxies discovered by JWST in the SPT2349-56 protocluster at z=4.30
Year: 2026
Type: preprint
Abstract: We present 11 newly identified ultra-red galaxies selected with JWST/NIRCam in the core of the z=4.3 protocluster SPT2349-56. Although these sources are not yet spectroscopically confirmed, their extremely red colours (m200-m444 > 2.0 mag), strong spatial concentration, and number density - at least 2000 times that of comparable field populations - make a chance projected association unlikely. Their colours overlap those used to select the widely studied ``little red dot'' (LRD) population, although most of the sources are spatially resolved and are therefore better described as extended red dots (ERDs). The resolved morphologies disfavour continuum emission dominated by an unresolved active nucleus and imply a substantial stellar contribution. Deep ALMA observations put strong limits on obscured star formation, and the ERD population mostly lies significantly below the star-forming main sequence. One object, ERD1/Q1, is substantially brighter and more massive, lying far below the main sequence, making it a strong candidate for a massive quiescent galaxy. These JWST-selected red galaxies reveal a previously inaccessible population extending to lower luminosities and stellar masses than the Dusty Star Forming Galaxy (DSFG) population which characterizes the dense protocluster core. SPT2349-56 may therefore capture an early phase of cluster assembly in which extreme starbursts coexist with galaxies already transitioning toward the passive galaxies characteristic of mature cluster cores.
Source: arXiv (Cornell University)
Authors: Chapman, Scott C., Phadke, Kedar A., Sulzenauer, Nikolaus, Zhou, Dazhi, Akins, Hollis, Aravena, Manuel, Burgoyne, James R., Casey, Caitlin M., Foley, Erin, Fryer, Leah, Hill, Ryley, LeVar, Nicholas, Llave, Monica Natalia Isla, Malkan, Matt, Pillai, Vismaya, Rasakanya, William, Solimano, Manuel, Spilker, Justin S., Torti, Aurelie, Vieira, Joaquin D., Vito, Fabio, Vizgan, David, Wang, George
Institutions: Max Planck Institute for Radio Astronomy, University of British Columbia, The University of Texas at Austin, Universidad Diego Portales, University of Victoria, University of California, Santa Barbara, Dalhousie University, Texas A&M University, University of California, Los Angeles, University of Pretoria, Centro de Astrobiología, University of Illinois Urbana-Champaign, National Center for Supercomputing Applications, Osservatorio di Astrofisica e Scienza dello Spazio, National Institute for Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, National Aeronautics and Space Administration, National Centre for Supercomputing Applications, Space Telescope Science Institute, National Radio Astronomy Observatory, Korea Astronomy and Space Science Institute, National Astronomical Observatory of Japan, University of Illinois at Urbana-Champaign, Canadian Space Agency, Natural Sciences and Engineering Research Council of Canada, National Institutes of Natural Sciences, Kavli Institute for Theoretical Physics, University of California, Santa Barbara
OpenAlex ID: W7213905482