Effect of the large-scale cosmic web environment on the X-ray-emitting circumgalactic medium

¹ Max Planck Institute for Extraterrestrial Physics (MPE), Gießenbachstraße 1, 85748 Garching, Munich, Germany
² Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
³ Department of Physics, Yale University, New Haven, CT 06520, USA
⁴ Department of Astronomy, Yale University, New Haven, CT 06520, USA
⁵ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Munich, Germany
⁶ Institut d’Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France
⁷ INAF-Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 June 2025
Accepted: 1 February 2026

Abstract

Aims. The hot circumgalactic medium (CGM), probed by X-ray observations, plays a central role in understanding gas flows that drive a galaxy’s evolution. While CGM properties have been widely studied, the influence of a galaxy’s large-scale cosmic environment on the hot gas content remains less explored. We investigate how the large-scale cosmic web affects the X-ray surface brightness (XSB) profiles of galaxies in the context of cosmological simulations.

Methods. We used our novel IllustrisTNG-based lightcone, first developed in our previous work and spanning 0.03 ≤ z ≤ 0.3, to generate self-consistent mock X-ray observations, using intrinsic gas cell information. We applied the filament-finder DisPerSE on the galaxy distributions to identify cosmic filaments within the lightcone. We classified central galaxies into five distinct large-scale environment (LSE) categories: clusters and massive groups, cluster outskirts, filaments, filament-void transition regions, and voids and walls.

Results. We find that the X-ray surface brightness profiles (XSB) of central galaxies of dark matter halos in filaments with M_200 m > 10¹²  M_⊙ are X-ray brighter than those in voids and walls, with 20 − 45% deviations in the radial range of (0.3 − 0.5)×R_200 m. We investigated the source of this enhancement and found that filament galaxies have higher average gas densities, temperatures, and metallicities than void and wall galaxies.

Conclusions. Our results demonstrate that the impact of the large-scale cosmic environment is imprinted on the hot CGM’s X-ray emission. Future theoretical works studying the effects of assembly history, connectivity, and gas accretion on galaxies in filaments and voids would help further our understanding of the impact of the environment on X-ray observations.