Star formation quenching precedes morphological transformation in COSMOS-WEB's richest galaxy groups
Abstract
We analyzed the 25 richest galaxy groups in COSMOS-Web at z = 0.18-3.65, identified via the AMICO algorithm. These groups contain 20-30 galaxies with high (>75%) membership probability. Our study reveals both passive-density and active-density relations: late-type galaxies (LTGs) prefer higher central overdensities than early-type galaxies (ETGs) across all groups, and many massive LTGs exhibit colors typical of quiescent galaxies. We identify red sequences (RS) in 5 groups, prominently established at z < 1, with early emergence in the RS locus up to z ~ 2.2. This suggests group environments represent a transitional phase where star formation quenching precedes morphological transformation, contrasting with the classical morphology-density relation in rich clusters. In the central regions (~33 arcsec / 100 kpc from centers), we identified 86 galaxies: 23 (~27%) ETGs and 63 (~73%) LTGs. High-mass galaxies (M_star > 10^10.5 M_sun) undergo rapid quenching over ~1 Gyr, becoming predominantly spheroidal ETGs. This indicates morphological transformation accelerates in massive systems during peak cosmic star formation. Intermediate-mass galaxies (10^9 < M_star/M_sun < 10^10.5) show mild quenching, while low-mass galaxies (M_star < 10^9 M_sun) remain largely star-forming; here, environmental processes suppress star formation without destroying disks, suggesting group quenching operates on longer timescales than mass quenching. Overall, mass-dependent quenching dominates the high-mass end, while environment shapes lower-mass systems. The HLAGN fraction for both groups and field increases with redshift, peaking at z ~ 2, with groups consistently showing higher fractions. We suggest AGN feedback partially drives rapid quenching in high-mass galaxies, while mergers may trigger AGN activity.
Keywords
Cite
@article{arxiv.2601.06297,
title = {Star formation quenching precedes morphological transformation in COSMOS-WEB's richest galaxy groups},
author = {Z. Ghaffari and G. Gozaliasl and A. Biviano and G. Toni and S. Taamoli and M. Maturi and L. Moscardini and A. Zacchei and F. Gentile and M. Haas and H. Akins and R. C. Arango-Toro and Y. Cheng and C. Casey and M. Franco and S. Harish and H. Hatamnia and O. Ilbert and J. Kartaltepe and A. H. Khostovan and A. M. Koekemoer and D. Liu and G. A. Mamon and H. J. McCracken and J. McKinney and J. Rhodes and B. Robertson and M. Shuntov and L. Yang},
journal= {arXiv preprint arXiv:2601.06297},
year = {2026}
}