Star Formation and Quenching in COSMOS Groups: Environmental Trends beyond z~2 Dicky Setiawan(a), Fahmi Aziz Firmansyah(a), Widya Syafna Azhalia(a), Sarah Biddle(b), Itsna K Fitriana(c,d)
a) Astronomy Study Program ITB
b) Center for Astrophysics Harvard
c) National Astronomical Observatory of Japan
d) Faculty of Mathematics and Natural Sciences ITB
Abstract
Galaxy evolution is influenced by both internal processes and external environmental factors. A key question is how environment impacts star formation and quenching, and how this evolves over cosmic time. This study investigates these effects by analyzing the specific star formation rate (sSFR) and quiescent fraction of galaxies as a function of group richness, using the COSMOS-Web galaxy group catalog from Toni et al. (2025), which includes over 1600 galaxy groups up to redshift z ~ 3.7. This allows us to explore environmental effects into the early protocluster formation epoch.
We cross-match galaxies in the catalog with photometric and SFR data from COSMOS-Web (Shuntov et al. 2025), apply detection flags to select robust samples, and compute sSFR from stellar mass and SFR estimates. Quiescent galaxies are identified using color-color cuts or an sSFR threshold (sSFR < 10^-11 yr^-1). Galaxies are binned by group richness (based on proxies like lambda* and amplitude A) and redshift intervals to measure average sSFR and quiescent fractions.
By comparing trends across redshifts, we aim to identify when environmental quenching becomes effective. These results will be compared to continuous-density trends from Taamoli et al. (2024) to test whether discrete group environments follow similar evolutionary patterns, such as the SFR-density relation reversal at z > 2. This work will help clarify the role of group-scale environments in galaxy quenching across cosmic time.
