COSMOS-Web: From early star-formation enhancement to late suppression in galaxy groups

Abstract

Galaxy groups trace dense environments where interactions, gas removal, and reduced accretion may drive quenching. Common diagnostics trace star formation over short timescales ($\lesssim 100$ Myr), so time-resolved star formation histories (SFHs) are needed to separate brief changes from longer-term evolution at fixed mass and redshift. Using COSMOS-Web data, we test how group environment correlates with star formation, how this evolves with cosmic time and group-centric distance, and how high-richness group galaxies differ from field galaxies. We combine COSMOS2025/COSMOS-Web stellar masses and non-parametric SFHs with AMICO group detections and probabilistic memberships. Using stacked SFHs and evolution diagnostics, we compare group and matched field galaxies as a function of normalized group-centric distance ($R_{\rm norm}$), using the richest groups as reference. The clearest suppression appears at $z<1.5$ and low-to-intermediate mass ($8.1<\log(M_\star/M_\odot)<10.5$), reaching a group-field SFH deficit up to 0.8 dex. At $z>1.5$, SFHs show weak suppression or occasional enhancement, a more heterogeneous contrast despite possible systematics. The radial signal also evolves: low-redshift profiles are broadly quenching-oriented across radius, while a clear inner-outer contrast emerges at $z\gtrsim 1$, though ordering at $z\gtrsim 2$ remains tentative given growing uncertainty in AMICO centroids. These results suggest an evolving picture: at early epochs groups are more mixed, with both suppressed and elevated SFHs; from $z\lesssim 1.5$, suppression dominates, most clearly for low-to-intermediate-mass galaxies. This fits inner-region galaxies spending more time within the group potential, undergoing more passages through dense intra-group regions, and receiving less pristine cold gas, making quenching progressively clearer with cosmic time.