Examples from the ISSI Team’s public library of mock ICL images, which provides realistic test data for developing and benchmarking detection techniques across the community.

Using the masked-aperture photometry method now adopted by the Euclid Collaboration, Bellhouse et al. (2025) predicts that the Euclid Wide Survey will enable intracluster light (ICL) measurements in up to 80,000 galaxy clusters. Shown here are examples from the team’s public library of mock ICL images, which provides realistic test data for developing and benchmarking detection techniques across the community.

Published: 25 September 2025

by Nina HatchFabio Crameri

Highlights
From the Teams
Intracluster light
Dark Matter
Star
Galaxies

Turning Ghostly Light into a Cosmic Tool

When you look at a galaxy cluster, most of the starlight comes from the galaxies themselves. But if you look deep enough, you will find a much fainter glow: the intracluster light (ICL). These are stars that no longer belong to any one galaxy, drifting freely in the space between them. Once seen as little more than an astronomical curiosity, ICL is now emerging as a powerful probe of how galaxy clusters grow and how dark matter is distributed.