Intracluster light is a biased tracer of the dark matter distribution in clusters

Butler, J.; Martin, G.; Hatch, N.A.; Pearce, F.; Brough, S.; Dubois, Y.

Abstract

The diffuse stellar component of galaxy clusters known as intracluster light (ICL) has been proposed as an observable tracer of the cluster’s dark matter (DM) halo. Assessing its reliability as a DM tracer requires understanding how the intracluster stars are energetically linked to the underlying DM distribution, which we investigate at z ≈ 0 in 12 galaxy clusters with M178 = 1.18 − 3.71 × 1014 M⊙ from the Horizon-AGN simulation. We quantify the orbital energies of these components by their mean specific energies 〈ϵ〉, and find that this quantity is ≈ 25 per cent lower for the intracluster stars than the DM, whilst the energetics of the satellite galaxies (a standard DM tracer) are only marginally (≈ 5 per cent) higher than the DM. Importantly, the lower 〈ϵ〉 of the intracluster stars compared to the DM is robust against the precise separation between the brightest cluster galaxy (BCG) and the ICL. The specific energy distribution of ICL stars is concentrated towards lower energies and poorly samples the higher energies, where much of the DM resides. Consequently, the intracluster stars have velocity distributions with lower typical speeds and a more centrally-concentrated density profile than the DM. We also find that intracluster stars have more radially-biased orbits than the DM, indicating these components have distinct orbital distributions. This study demonstrates that although the morphology of the ICL may match the DM halo, the ICL is a biased tracer of DM, and these biases must be understood in order to infer properties of the DM from the ICL.

Citation

Butler, J., Martin, G., Hatch, N., Pearce, F., Brough, S., & Dubois, Y. (2025). Intracluster light is a biased tracer of the dark matter distribution in clusters. Monthly Notices of the Royal Astronomical Society, 539(3), 2279-2291. https://doi.org/10.1093/mnras/staf615

• Journal Article Type: Article
• Acceptance Date: Apr 12, 2025
• Online Publication Date: Apr 14, 2025
• Publication Date: 2025-05
• Deposit Date: Apr 17, 2025
• Publicly Available Date: Apr 7, 2025
• Journal: Monthly Notices of the Royal Astronomical Society (MNRAS)
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 539
• Issue: 3
• Pages: 2279-2291
• DOI: https://doi.org/10.1093/mnras/staf615
• Keywords: galaxies, clusters, interactions, kinematics and dynamics
• Public URL: https://nottingham-repository.worktribe.com/output/47816250
• Publisher URL: https://academic.oup.com/mnras/article/539/3/2279/8113287