Intracluster Light: a luminous tracer for dark matter in clusters of galaxies

The vast majority of the mass in the Universe is expected to be in form of dark matter. Invisible as it is, it would be ideal to identify a luminous tracer that will mimic their spatial distribution. The distribution of stars within the galaxies is not a good tracer of the dark matter as they are originated in a dissipative process that locate most of the stars in the centre of the haloes. However, we expect that some stars whose spatial distribution results from the interactions of galaxies in the cluster follow the underlying dark matter distribution. These stars form the so called intracluster light (ICL). Here we compare the distribution of the dark matter mass in massive galaxy clusters (as traced by gravitational lensing models) with the distribution of ICL, using the exquisite data from the Hubble Frontier Fields. Using a shape matching measurement to assess the similarities, the Modified Hausdorff distance, we find an excellent agreement between the spatial distribution of the total mass and the intracluster light distribution. This gives us the first reliable luminous tracer of dark matter halos in galaxy clusters. Our finding opens the possibility to explore the dark matter distribution of galaxy clusters using only their low surface brightness light.