2026A&A...706A.344S

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.