Tracing the invisible: The shape of cluster haloes revealed by the intracluster light — Tutku Kolcu (University of Nottingham)

The intracluster light (ICL) is a uniquely luminous probe of galaxy cluster halo shape and orientation, but it’s extremely low surface brightness has historically made robust morphological measurements challenging. In this talk, I present ICL shape measurements from Euclid’s Quick Release (Q1) for nearly 200 clusters at 0.1 ≤ z ≤ 0.8, selected from the eROSITA All-Sky Survey and the Dark Energy Survey. The ICL ellipticity distribution peaks at e ≃ 0.5, in close agreement with halo ellipticities from strong and weak lensing — supporting the view that the ICL traces the cluster’s large-scale structure. Radially, BCG-dominated cores are relatively round, while the diffuse component becomes progressively more elongated before plateauing at large radii. By stacking clusters in redshift bins, we extend these measurements to larger cluster-centric radii and find no detectable evolution with redshift — a result that challenges theoretical expectations. Comparing to the Hydrangea simulations, we show that the ICL’s measured shape depends sensitively on how it is defined and extracted: only fully forward-modelled mock observations reproduce the observed distribution, underscoring that realistic mock observations are essential for direct comparison with theory. This methodology provides a benchmark for testing hydrodynamical simulations, and forthcoming Euclid data releases will enable substantially tighter constraints.

Horarios: 18 Aug 2026

Publicado por: Gijs Mulders