[Astro] Lunch Talk - 30/10/25

[Joseph Butler]

Hi all,

This week’s lunch talk will be given by Tutku Kolcu, and will take place on Thursday 30th October at 1pm in A113. Title and abstract below.

Title: Tracing the invisible: The shape of cluster haloes revealed by intracluster light

Abstract: The intracluster light (ICL) provides a powerful means of tracing the diffuse stellar component of galaxy clusters and directly probing the shapes of their underlying dark matter haloes. The morphology of the ICL—its ellipticity, orientation, and radial variation—encodes valuable information about cluster assembly, dynamical state, and the coupling between baryons and dark matter. However, its extremely faint nature has long hindered systematic studies of structure on cluster scales. With the advent of high-resolution, wide-field imaging from Euclid, we can now measure ICL shapes with unprecedented precision. In this talk, I will present results from Euclid’s Quick Release (Q1), where we quantify ICL ellipticity and position angle for nearly 200 clusters between redshifts 0.1 and 0.8 across five photometric bands (VIS, Y, J, H, and coadded YJH). We find consistent shape parameters across filters, with the H band tracing the ICL to the largest cluster-centric distances. The ICL becomes progressively more elongated with radius, reaching ellipticities consistent with those inferred from weak and strong lensing studies, and showing alignment with both the brightest cluster galaxy and the member galaxy distribution. Comparisons with Hydrangea hydrodynamical simulations reveal similar, though slightly rounder, ICL shapes. These results establish the ICL as a robust luminous tracer of halo structure and orientation.

Thanks,
Joe
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