[Paper Review] From Clusters to Proto-clusters: the Infrared Perspective on Environmental Galaxy Evolution

Stacey Alberts, Allison Noble|arXiv (Cornell University)|Sep 6, 2022

Galaxies: Formation, Evolution, Phenomena4 citations

TL;DR

This review synthesizes the role of environment in galaxy evolution through the lens of infrared observations, focusing on quenching mechanisms in galaxy clusters and their high-redshift progenitors, proto-clusters. It demonstrates that infrared data reveal obscured star formation, molecular gas content, and quenching pathways across cosmic time, revealing complex, environment-dependent evolutionary pathways in (proto-)clusters.

ABSTRACT

Environment is one of the primary drivers of galaxy evolution; via multiple mechanisms, it can control the critical process of transforming galaxies from star forming to quiescent, commonly termed "quenching". Despite its importance, however, we still do not have a clear view of how environmentally-driven quenching proceeds even in the most extreme environments: galaxy clusters and their progenitor proto-clusters. Recent advances in infrared capabilities have enabled transformative progress not only in the identification of these structures but in detailed analyses of quiescence, obscured star formation, and molecular gas in (proto-)cluster galaxies across cosmic time. In this review, we will discuss the current state of the literature regarding the quenching of galaxies in (proto-)clusters from the observational, infrared perspective. Our improved understanding of environmental galaxy evolution comes from unique observables across the distinct regimes of the near-, mid-, and far-infrared, crucial in the push to high redshift where massive galaxy growth is dominated by highly extincted, infrared-bright galaxies.

Motivation & Objective

• To synthesize current observational evidence on environmental galaxy quenching using infrared data across cosmic time.
• To clarify the role of multiple quenching mechanisms—internal and external—in shaping galaxy evolution in high-density environments.
• To examine how infrared observables (near-, mid-, far-IR) reveal obscured star formation and molecular gas in (proto-)cluster galaxies.
• To assess the transition from star-forming to quiescent populations in clusters and proto-clusters from z ≈ 0 to z > 2.
• To establish the boundary conditions for environmentally driven quenching using massive galaxy clusters as astrophysical laboratories.

Proposed method

• Systematic review of multi-wavelength infrared data from space-based observatories (IRAS, Spitzer, Herschel, WISE, JWST) and ground-based facilities (ALMA, NOEMA, JCMT).
• Analysis of spectral energy distributions (SEDs) and spectral line data (e.g., CO, [CII]) to infer star formation rates, molecular gas content, and dust properties.
• Use of photometric and spectroscopic redshifts to place galaxies in cosmic time and environmental density bins (voids, filaments, groups, clusters).
• Comparison of star-forming fractions and SFR-density relations across environments and redshifts using large surveys (e.g., HeViCS, VERTICO, GASP, COSMOS).
• Integration of data from submillimeter and millimeter surveys (e.g., ALMA, PACS, SPIRE) to probe cold gas and obscured star formation in high-redshift proto-clusters.
• Application of environmental density estimators and stellar mass binning to quantify the morphology- and SFR-density relations across cosmic time.

Experimental results

Research questions

• RQ1 How does the star formation rate (SFR) and quiescent fraction of galaxies vary with local environmental density from z ≈ 0 to z > 2?
• RQ2 What role do infrared-observed molecular gas and dust-obscured star formation play in the quenching of galaxies in proto-clusters at z ≳ 2?
• RQ3 To what extent do multiple quenching mechanisms (e.g., ram pressure stripping, strangulation, AGN feedback) operate in (proto-)clusters, and how do they vary with environment and redshift?
• RQ4 How do the observed SFR-density and morphology-density relations evolve from low to high redshift, and what do they reveal about the timing of quenching?
• RQ5 What is the contribution of proto-clusters to the cosmic star formation rate density (SFRD) at z ≳ 2, and how does it compare to that of mature clusters?

Key findings

• The star-forming fraction of galaxies decreases progressively with increasing local galaxy density, from nearly 100% in voids to <50% in massive clusters at z ≈ 0.
• In proto-clusters at z ≳ 2, substantial star formation is observed, with infrared-bright, dust-enshrouded galaxies dominating the star formation rate density (SFRD).
• Galaxy clusters at z ≈ 1–2 show a breakdown or reversal of the SFR-density relation, indicating that quenching mechanisms ramp up rapidly during this epoch.
• Infrared observations reveal that quiescent galaxies in clusters have low atomic and molecular gas content, consistent with quenching via environmental processes.
• The fraction of massive galaxies in proto-clusters at z ≈ 10 may have contributed up to half of the cosmic SFRD, highlighting their importance in early massive galaxy growth.
• Multi-wavelength infrared data from JWST and ALMA are essential for resolving obscured star formation and molecular gas in high-redshift (proto-)clusters, enabling detailed quenching pathway analysis.