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

TL;DR

Using JWST data, the Cosmic Vine protocluster at $z=3.44$ is characterized to understand early cluster assembly. The study confirms $136$ Vine members and $47$ Leaf members, identifies six subgroups, and finds $11$ quiescent galaxies forming an early red sequence, with a high quiescent fraction and top-heavy SMFs. Halo masses are estimated around $\log(M_h/M_\odot)\approx13.2$ for the core and $11.9$–$12.4$ for satellites; phase-space suggests several subgroups are infalling, indicating ongoing assembly. The results imply accelerated formation of massive galaxies in massive halos in the first $\sim2$ Gyr, and the Vine will likely evolve into a Coma-like cluster by $z\sim0$.

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 conduct 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 confirm 136 galaxies in the Vine at z=3.44, and an additional 47 galaxies belonging to a diffuse foreground structure at z=3.34 which we dub the Leaf. We identify four subgroups comprising the Cosmic Vine and two subgroups within the Leaf. Second, we identified 11 quiescent members with log(M*/Msun)=9.5-11.0, the largest sample of quiescent galaxies in overdense environments at z>3, which gives an enhanced quiescent galaxy number density 2x10^(-4)cMpc^(-3) that is three times above the field level at log(M*/Msun) > 10. Notably, these quiescent members form a tight red sequence on the color-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*/Msun)>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 estimate a halo mass of log(Mh/Msun)=13.2+-0.3 for the protocluster core, and log(Mh/Msun)=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 a forming cluster, demonstrating the accelerated assembly of massive galaxies in massive halos when the Universe was less than 2 billion years old.

Figures (8)

• Figure 1: Left: Colour image of the densest region of the Vine and the Leaf. The colours correspond to JWST/F150W, F277W, F444W as the blue, green, and red channels respectively. The projected density is shown as white contours at $2,3,~{\rm and}~4\,\sigma$ levels. The virial radii of the six most massive identified dark matter halos are marked with magenta dashed circles. Quiescent members of the Cosmic vine are marked with orange circles, spectroscopically confirmed members of the Cosmic Vine are marked with green circles, spec-z confirmed members of the Leaf are marked with yellow circles, and candidate members with cyan circles. Right: NIRCam/F150W, F277W, F444W colour images of 11 quiescent galaxies in the Cosmic Vine. The field of view of each cutout is 2".
• Figure 2: Left: Rest-frame UVJ diagram of protocluster members. The color selection function is shown in black lines. Identified quiescent galaxies are marked with a star. The sSFRs of the galaxies is coded in colour. The cross in the bottom right corner shows the average uncertainty Right: Color-magnitude diagram of quiescent (red stars) and star-forming (blue dots) members. The background hexagons show the density of field galaxies. Overlaid is a linear fit to the quiescent galaxies (black dashed) and the scatter (gray dot-dashed), with the slope and intercept at $M_{\rm F200W}=21$ shown in text. The observational depth is shown with a gray dotted line.
• Figure 3: Stellar mass functions (SMFs) and quiescent fractions. Left: SMFs for the star-forming (light blue) and quiescent (red) members of the Vine, fitted with a Schechter function. The black dots and line show the CEERS SFG field sample, and the orange dots and line show the CEERS QG sample. The vertical lines mark the stellar mass completeness limit of the field (black) and Cosmic Vine members (blue). Right: Quiescent fractions of Cosmic Vine members (red) and the rest of the CEERS field (black). Blue dots with error bars represent the quiescent fractions from the JWST/PRIMER fields at $z\sim3.45$Yang2025.
• Figure 4: Mass-size relation of star-forming members (blue), quiescent members (red), field SFGs (black), and field QGs (green). Powerlaw fits to SFG members and field SFGs are shown with blue solid and black dotted lines respectively, with the fit uncertainty of SFG members shown as shaded region. Mass-size relations of late type galaxies from Ward2024_Mass_size_relation (green line) and quiescent galaxies from Ito2024_QG_mass_size (red line) are over plotted, the relations are extrapolated for SFGs with $M_\ast<10^{9.5}\,{\rm M_\odot}$ and QGs with $M_\ast<10^{10.3}\,{\rm M_\odot}$. The vertical dashed lines show the mass completeness limit of the CEERS field (gray) and Cosmic Vine (blue).
• Figure 5: Phase-space diagrams for spectroscopically confirmed members and subgroups. Left: The galaxies are sized and coloured according to the stellar mass. Measured velocity differences are multiplied with a factor of $\sqrt{3}$, to account for measuring projected velocities Rhee2017. Right: Phase-space diagram for the subgroups with sizes coded with the estimated halo mass (\ref{['tab:halos']}). The errorbars on the subgroups show the estimated virial radius in the radial direction, and the uncertainty on the central velocity in the velocity direction. Overlaid are $v_{\rm esc,NFW}$ calculated as a NFW profile with $c_{\rm halo}=20.46$ shown as a black dashed line, and $v_{\rm esc,point}$ as a point mass distribution ($c_{\rm halo}\rightarrow\infty$) shown as a black dotted line. The virial region of the core is defined as $v_{\rm r} < v_{\rm r,crit} ~\&~ R<R_{\rm vir}$ from *Sanchis2004, which is shown with a red shaded area.