Intracluster Light as a Probe for Dark Matter: Exploring Self-interacting Dark Matter and Cold Dark Matter with C-EAGLE Sims

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Abstract
In this pilot study, we investigate whether intracluster light (ICL) can serve as an observational discriminator of dark matter physics. The self-interacting dark matter (SIDM) model has gained increasing attention as a possible resolution to small-scale discrepancies between collisionless cold dark matter (CDM) simulations and observations, predicting distinct tidal interaction histories within galaxy clusters. We analyze Cluster-EAGLE zoom-in galaxy clusters resimulated from identical initial conditions in both CDM and SIDM frameworks. The morphological similarity between dark matter and multiple baryonic tracers (gas, all stars, galaxies, and the combined brightest cluster galaxy plus ICL, BCG+ICL) is quantified using the weighted overlap coefficient, a contour-overlap statistic. We find that dark matter is traced most accurately by BCG+ICL, followed by gas, all stars, and galaxies. Although the differences are modest, they are systematic: The collisionless tracers (all stars, galaxies, and BCG+ICL) show better correspondence with the dark matter distribution in CDM, while the relative advantage of BCG+ICL over gas is reduced in SIDM. This reduction is driven primarily by weaker BCG+ICL–dark matter correspondence in SIDM. Qualitatively, this behavior is consistent with the expectation that collisionless stellar components more naturally trace collisionless dark matter in CDM, whereas self-interactions in SIDM introduce an effective viscosity that weakens the dominance of BCG+ICL as a dark matter tracer relative to gas. Our results demonstrate the potential of ICL as a novel observational probe of dark matter physics and provide a first step toward using diffuse cluster light to constrain the nature of dark matter.
Funding Information
  • National Research Foundation of Korea (2018R1A6A1A06024977)
  • Australian Research Council Centre of Excellence for Dark Matter Particle Physics (CE200100008)
  • National Research Foundation of Korea (RS-2024-00360385)
  • National Research Foundation of Korea (2021R1C1C2011626)

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