Cosmic Vine: High abundance of massive galaxies and dark matter halos in a forming cluster at z = 3.44

¹ Cosmic Dawn Center (DAWN) Copenhagen, Denmark
² DTU Space, Technical University of Denmark Elektrovej 327 DK-2800 Kgs. Lyngby, Denmark
³ CEA, IRFU, DAp, AIM, Université Paris-Saclay, Université Paris Cité, Sorbonne Paris Cité, CNRS 91191 Gif-sur-Yvette, France
⁴ Instituto de Física, Pontificia Universidad Católica de Valparaíso Casilla 4059 Valparaíso, Chile
⁵ Instituto de Física y Astronomía, Universidad de Valparaíso Avda. Gran Bretaña 1111 Valparaíso, Chile
⁶ Millennium Nucleus for Galaxies (MINGAL), Chile
⁷ School of Astronomy and Space Science, Nanjing University Nanjing 210093, China
⁸ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education Nanjing 210093, China
⁹ Niels Bohr Institute, University of Copenhagen Jagtvej 128 2200 Copenhagen, Denmark

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Received: 27 October 2025
Accepted: 5 January 2026

Abstract

The Cosmic Vine is a massive protocluster at z = 3.44 in the JWST CEERS field, offering an ideal laboratory for studying the early phases of cluster formation. Using the data from the DAWN JWST Archive, we conducted a comprehensive study on the large-scale structure, stellar mass function (SMF), quiescent members, and dark matter halos in the Cosmic Vine. First, we spectroscopically confirmed 136 galaxies in the Vine at z ≈ 3.44, along with an additional 47 galaxies belonging to a diffuse foreground structure at z ≈ 3.34, which we dubbed the Leaf. We identified four subgroups comprising the Cosmic Vine and two subgroups within the Leaf. Second, we identified 11 quiescent members with log(M_*/M_⊙) = 9.5 − 11.0, the largest sample of quiescent galaxies in overdense environments at z > 3, which gives an enhanced quiescent galaxy number density ∼1 − 2 × 10⁻⁴ cMpc⁻³ that is two to three times above the field level at log(M_*/M_⊙) > 10. Notably, these quiescent members form a tight red sequence on the colour-magnitude diagram, making it one of the earliest red sequences known to date. Third, by constructing the SMFs for both star-forming and quiescent members, we find that both SMFs are top-heavy, with a significantly enhanced quiescent fraction at log(M_*/M_⊙) > 10.5 compared to field counterparts. The stellar mass–size analysis reveals that star-forming members are more compact at higher masses than their field counterparts. Finally, we estimated a halo mass of log(M_h/M_⊙) = 13.2 ± 0.3 for the protocluster core and log(M_h/M_⊙) = 11.9 − 12.4 for satellite subgroups. The phase-space analysis indicates that three subgroups are likely infalling to the core. This work reveals a high abundance of massive galaxies and dark matter halos in this forming cluster, demonstrating the accelerated assembly of massive galaxies in massive halos when the Universe was less than 2 billion years old.