The COSMOS Wall at z ∼ 0.73: Quiescent galaxies and their evolution in different environments

The evolution of quiescent galaxies is driven by numerous physical processes, often considered to be related to their stellar mass and environment over cosmic time. Tracing their stellar populations can provide insight into the processes that transformed these galaxies into their observed quiescent state. In particular, higher-redshift galaxies, being younger, exhibit more pronounced relative age differences. At early stages, even small differences in age remain significant, whereas as galaxies evolve, these differences become less detectable, making it harder to trace the impact of environmental effects in the local Universe. The COSMOS Wall is a structure at z ∼ 0.73 that contains a large variety of environments, from rich and dense clusters down to field-like regions. Thus, this sample offers a great opportunity to study the effect of the environment on the quiescent galaxy population. Leveraging high-quality spectroscopic data from the LEGA-C survey, combined with the extensive photometric coverage of the COSMOS2020 catalogue, we performed a full-index and photometry fitting of 74 massive (log M∗/M⊙ = 10.47) quiescent galaxies, deriving their mass-weighted ages, metallicities, and star formation timescales. We characterised the environment in three subsamples: X-ray- and non-X-ray-detected groups and a lower-density subsample similar to the average field. We find a decreasing trend in mass-weighted age with increasing environmental density, with galaxies groups ≥1 Gyr older than those in the field. Conversely, we do not find any significant difference in stellar metallicity between galaxies in X-ray and non-X-ray groups, while we find galaxies with 0.15 dex higher metallicities in the field. Our results indicate that, at ∼0.7, the environment plays a crucial role in shaping the evolution of massive quiescent galaxies, noticeably affecting both their mass-weighted age and star formation timescale. These results support faster quenching mechanisms, at fixed stellar mass, in the dense X-ray-detected groups compared to the field.