Tracing the Cosmic web across Cosmic time through SKA observations of radio galaxies

Pratik Dabhade, Gianluca Castignani, Mousumi Mahato, Shishir Sankhyayan, D. J. Saikia, Viviana Casasola, Francoise Combes

First listed 2026-07-30 | Last updated 2026-07-28

Abstract

The Square Kilometre Array will transform studies of the cosmic web by tracing radio galaxies (RGs) and star-forming systems across cosmic time with unprecedented sensitivity, angular resolution, frequency coverage, and survey speed. Powered by accreting supermassive black holes, RGs are not only signposts of AGN feedback but also incisive probes of their environments, from dense clusters to the low-density intergalactic medium. Their lobes, magnetic fields, and energy outflows encode the thermal and non-thermal histories of the surrounding gas, offering diagnostics of IGM pressure, particle ageing, and magnetisation over megaparsec scales. With its broad frequency coverage (50 MHz-15 GHz), microJy to sub-microJy continuum sensitivity, and wide field of view, the SKA will detect vast radio-source populations across broad ranges of redshift and environment. Measurements of source size, morphology, spectral ageing, radio power, polarisation, and Faraday rotation will reveal how the environment regulates jet propagation and lobe evolution, how radio plasma heats and magnetises the intracluster and intergalactic media, and how early AGN activity influences galaxy growth and star formation in protoclusters. Combined with host identifications, spectroscopic redshifts, and optical, infrared, X-ray, Sunyaev--Zel'dovich, and cosmic-web catalogues, SKA observations will place RGs within their three-dimensional large-scale environments. This chapter presents a framework for using RGs to trace and probe the cosmic web, from nearby filaments and clusters to high-redshift protoclusters, and to test how environment, magnetic fields, feedback, and gas dynamics shape radio-galaxy evolution, protocluster assembly, and star formation across cosmic time.

Short digest

This SKA-focused chapter lays out how radio galaxies can be used as both tracers and probes of the cosmic web, linking their sizes, morphologies, spectral ageing, polarisation, and Faraday rotation to the gas and magnetic environments in which their jets propagate. It argues that SKA’s 50 MHz–15 GHz coverage, sub-microJy continuum depth, angular resolution, and dense rotation-measure grids will enable population-level measurements of jet–environment coupling from nearby filaments and clusters to high-redshift protoclusters. The central payoff is a three-dimensional, multiwavelength view of how radio-mode feedback heats and magnetises intracluster and intergalactic gas while connecting early AGN activity to protocluster assembly and star formation; angular resolution alone, however, does not guarantee morphological classification because surface brightness and imaging sensitivity remain limiting factors.

Key figures to inspect

• Figure 1. Shows the redshift-dependent physical-size thresholds for resolving radio-galaxy morphology in representative SKA1 bands. It is the practical observational foundation for the chapter’s proposed use of FR structures, compact sources, and giant lobes as environmental tracers, while clearly separating angular resolvability from sensitivity and surface-brightness limitations.
• Figure 2. Places FR I, FR II, and wide-angle-tail radio galaxies alongside nearby filament spines and cluster catalogues, directly visualising the chapter’s core premise that radio morphology can be interpreted within large-scale environment. Its explicitly non-homogeneous, illustrative sample is also a useful reminder that robust environmental inferences require three-dimensional, source-by-source association.
• Figure 3. Uses the z=3.8 radio galaxy 4C 41.17 to connect resolved radio structure with a high-redshift protocluster-scale environment. The overlay of VLA radio contours on HST imaging provides a concrete example of the multiwavelength host identification and structural information that SKA-era surveys will extend statistically.