A Census of the 200 Most Massive Galaxies Spectroscopically Observed with JWST at zspec $\sim$3-15
Year: 2026
Type: preprint
Abstract: Massive galaxies provide strong tests of galaxy formation models, yet a comprehensive spectroscopic view of their properties and demographics in the early Universe has remained elusive. Here we present a JWST spectroscopic census of the 200 most massive galaxies at zspec~3-15, selected using an evolving stellar-mass threshold motivated by the halo mass function and anchored at log(Mstar)>10 at z~5. These galaxies represent the top 3% most massive systems among all publicly available prism observations. We derive their physical properties through joint SED fitting of spectroscopy and photometry, and construct a clean massive galaxy sample after removing LRDs and broad-line AGN contaminants. We find that the massive galaxy population evolves strongly with redshift: normal SFGs (Av<1 mag) dominate at z>~6, while dusty SFGs (Av>1 mag) and QGs become more common toward lower redshift. Dust attenuation decreases systematically toward higher redshift. We identify 29 massive QGs, including a population of recently quenched systems whose star formation declined rapidly within the past ~100 Myr. We further show that both the traditional UVJ and recently proposed (ugi)s selections suffer substantial inconsistency with the most massive galaxies at z>3, motivating a revised (ugi)s criterion calibrated using our spectroscopic sample. The inferred formation histories suggest at least two pathways toward quiescence: a dust-enriched pathway linking normal SFGs, dusty SFGs, and QGs, and a more direct pathway connecting normal SFGs and QGs. Massive normal SFGs appear to grow through both relatively gradual and rapid assembly modes. Together, these results suggest that rapid stellar-mass assembly, dust enrichment, and quenching were already shaping the evolutionary pathways of the most massive galaxies within the first billion years after the Big Bang.
Source: arXiv (Cornell University)
Authors: Xiao, Mengyuan, Oesch, Pascal A., Bing, Longji, Gottumukkala, Rashmi, Marques-Chaves, Rui, Brammer, Gabriel, Dessauges-Zavadsky, Miroslava, Elbaz, David, Qi, Songnan, Sawarkar, Anurag Amol, Aravena, Manuel, Béthermin, Matthieu, Bezanson, Rachel, Bouwens, Rychard, Casey, Caitlin, van Dokkum, Pieter, Faisst, Andreas L., Fudamoto, Yoshinobu, de Graaff, Anna, Ilbert, Olivier, Illingworth, Garth, Lagache, Guilaine, Magnelli, Benjamin, Matthee, Jorryt, Nakazato, Yurina, Schaerer, Daniel, Toft, Sune, Whitaker, Katherine E., Williams, Christina C.
Institutions: University of Sussex, University of Copenhagen, University of Geneva, Centre National de la Recherche Scientifique, Université Paris Cité, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, Astrophysique, Instrumentation et Modélisation, Universidad Diego Portales, Observatoire astronomique de Strasbourg, Université de Strasbourg, University of Pittsburgh, Leiden University, Leiden Observatory, University of California, Santa Barbara, Yale University, California Institute of Technology, Infrared Processing and Analysis Center, Chiba University, Center for Frontier Science, Chiba University, Max Planck Institute for Astronomy, Center for Astrophysics Harvard & Smithsonian, Aix-Marseille Université, University of California, Santa Cruz, Institute of Science and Technology Austria, Flatiron Institute, University of Massachusetts Amherst, University of Arizona, NSF NOIRLab
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Danmarks Grundforskningsfond, Agencia Nacional de Investigación y Desarrollo, Smithsonian Astrophysical Observatory, Japan Society for the Promotion of Science, Staatssekretariat für Bildung, Forschung und Innovation
Awards: G1424166960, JWST Gravitational Lensing Galaxy Cluster Monitoring Observations: Detection of Individual Stars and Exploration of Galaxy Formation History and Dark Matter, Cosmic Dawn Center (DAWN), G4648019588, ORCHIDS: ORIGIN OF THE [CII] HALOS IN DISTANT SYSTEMS, CENTRO DE ASTROFISICA Y TECNOLOGIAS AFINES (CATA)
OpenAlex ID: W7166842897