Galaxy Evolution in Cluster Environments

Galaxy clusters represent the most massive bound structures in the Universe and act as crucibles in which environmental forces shape the life cycles of their constituent galaxies. Within these dense regions, galaxies experience processes that can strip away gas reservoirs, truncate star formation and drive morphological change from disc to spheroid. Key mechanisms include ram pressure stripping by the hot intracluster medium, tidal interactions and galaxy–galaxy harassment, all of which accelerate the transition from star-forming to quiescent systems. Moreover, hierarchical assembly ensures that many galaxies undergo ‘pre-processing’ in infalling groups, altering their stellar and gaseous content before entering the cluster core. The interplay of mass-driven quenching and environment-driven quenching produces the well established morphology–density and star formation-density relations. By tracing these phenomena over cosmic time, researchers gain insight into how baryonic physics and dark-matter dynamics converge to regulate galaxy growth, enrich the intracluster medium and sculpt the large-scale structure of the cosmos.

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Analysis of deep JWST NIRCam imaging combined with optical integral-field spectroscopy in the cluster Abell 2744 has revealed a population of galaxies exhibiting an unexpected ‘red excess’ at mid-infrared wavelengths. Although these objects lie on or near the red sequence in optical colours, their enhanced long-wavelength emission is interpreted as dust-enshrouded star formation. Morphological signatures of gas stripping in the cluster core and signs of tidal interactions in the outskirts support a scenario in which both ram pressure and dynamical encounters can trigger buried starbursts before rapid quenching.

Multi-object spectroscopy of two galaxy clusters at redshift near one has uncovered markedly different fractions of quiescent galaxies despite similar total masses. Follow-up studies link this contrast to the richness of surrounding large-scale structures. Clusters embedded within extensive filamentary networks maintain a supply of infalling, star-forming galaxies and thus show a lower quiescent fraction at fixed mass. This anticorrelation highlights how the cosmic web mediates environmental quenching by regulating the inflow of fresh gas and galaxies into dense nodes.

The MAGIC survey of galaxy groups and clusters at intermediate redshift uses wide-field integral-field data to quantify pre-processing effects over the past eight billion years. It demonstrates that the fraction of quiescent and bulge-dominated galaxies increases with both local density and time since group infall. A clear shift in the stellar-mass distribution towards higher masses in denser substructures indicates that low-mass systems are preferentially quenched or disrupted before reaching the cluster core. These findings emphasise that transformation often begins in group environments and continues as galaxies migrate along the cosmic web.

Galaxy Evolution in Cluster Environments publication trend

The graph below shows the total number of articles in galaxy evolution in cluster environments across all publications each year (not limited to Nature Index journals).

Technical terms

Ram pressure stripping: Removal of a galaxy’s interstellar gas by the pressure exerted as it moves through the hot intracluster medium.

Quenching: Cessation of star formation in a galaxy, leading to its transition from a blue, star-forming state to a red, passive state.

Pre-processing: Evolutionary changes in galaxies (including quenching and morphological transformation) that occur within groups before they fall into richer cluster environments.

Virial radius: The characteristic radius of a cluster within which the system is gravitationally bound and in approximate virial equilibrium.

Large-scale structure: The network of filaments, sheets and voids in the cosmic matter distribution that channel galaxies and dark matter into clusters.

References

1. Early Results from GLASS-JWST. XX. Unveiling a Population of “Red Excess” Galaxies in Abell2744 and in the Coeval Field. The Astrophysical Journal Letters (2023).
2. Multiobject Spectroscopy of Galaxy Clusters at z ∼ 0.95 in the Ultra Deep Survey Field with Different Star Formation Properties and Large-scale Environments. The Astrophysical Journal Supplement Series (2024).
3. MAGIC: MUSE gAlaxy Groups In COSMOS – A survey to probe the impact of environment on galaxy evolution over the last 8 Gyr⋆⋆⋆. Astronomy & Astrophysics (2024).