Galaxy Clusters Abell S1063 and MACS J0416.1-2403

Tracing Diffuse Starlight in Galaxy Clusters

Two massive galaxy clusters — Abell S1063 (left) and MACS J0416.1-2403 (right) — display a soft blue haze, called intracluster light, embedded among innumerable galaxies. The intracluster light is produced by orphan stars that no longer belong to any single galaxy, having been thrown loose during a violent galaxy interaction, and now drift freely throughout the cluster of galaxies. Astronomers have found that intracluster light closely matches with a map of mass distribution in the cluster's overall gravitational field. This makes the blue "ghost light" a good indicator of how invisible dark matter is distributed in the cluster. Dark matter is a key missing link in our understanding of the structure and evolution of the universe. Abell S1063 and MACS J0416.1-2403 were the strongest examples of intracluster light providing a much better match to the cluster's mass map than X-ray light, which has been used in the past to trace dark matter.

About the colours

These images are composites of separate exposures acquired by the WFC3/IR and ACS/WFC instruments. Several filters were used to sample various wavelengths. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Blue: ACS/WFC F435W (B) + F606W (R) Green: ACS/WFC F814W (I) + WFC3/IR F105W (Y) Red: WFC3/IR F125W (J) + F140W (JH) + F160W (H)

About the data

Abell S1063 and MACS J0416 are part of the Frontier Fields Program. These data are from the HST proposals 12458 (PI: M. Postman, STScI), 13459 (PI: T. Treu, UCLA), 14037 (PI: J. Lotz, STScI), and 14209 (PI: B. Siana, UC Riverside).