A large overdensity of LRD-like galaxies discovered by JWST in the SPT2349-56 protocluster at z=4.30

@misc{chapman2026large,
  title = {{A large overdensity of LRD-like galaxies discovered by JWST in the SPT2349-56 protocluster at z=4.30}},
  author = {Scott C. Chapman and Kedar A. Phadke and Nikolaus Sulzenauer and Dazhi Zhou and Hollis Akins and Manuel Aravena and James R. Burgoyne and Caitlin M. Casey and Erin Foley and Leah Fryer and Ryley Hill and Nicholas LeVar and Monica Natalia Isla Llave and Matt Malkan and Vismaya Pillai and William Rasakanya and Manuel Solimano and Justin S. Spilker and Aurelie Torti and Joaquin D. Vieira and Fabio Vito and David Vizgan and George Wang},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.21337},
  eprint = {2609.21337},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.21337},
}

TY  - UNPB
TI  - A large overdensity of LRD-like galaxies discovered by JWST in the SPT2349-56 protocluster at z=4.30
AU  - Scott C. Chapman
AU  - Kedar A. Phadke
AU  - Nikolaus Sulzenauer
AU  - Dazhi Zhou
AU  - Hollis Akins
AU  - Manuel Aravena
AU  - James R. Burgoyne
AU  - Caitlin M. Casey
AU  - Erin Foley
AU  - Leah Fryer
AU  - Ryley Hill
AU  - Nicholas LeVar
AU  - Monica Natalia Isla Llave
AU  - Matt Malkan
AU  - Vismaya Pillai
AU  - William Rasakanya
AU  - Manuel Solimano
AU  - Justin S. Spilker
AU  - Aurelie Torti
AU  - Joaquin D. Vieira
AU  - Fabio Vito
AU  - David Vizgan
AU  - George Wang
PY  - 2026
DA  - 2026/09/21
PB  - arXiv
DO  - 10.48550/arxiv.2609.21337
UR  - https://arxiv.org/abs/2609.21337
AB  - 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.
ER  -