The intracluster light on Frontier Fields clusters Abell 370 and Abell S1063

We analysed the contribution of the intracluster light (ICL) to the total luminosity of two massive galaxy clusters observed by the Hubble Space Telescope within the Frontier Fields program, Abell 370 (z similar to 0.375) and Abell S1063 (z similar to 0.348), in order to correlate it with the dynamical stage of these systems. We applied an algorithm based on the Chebyshev-Fourier functions called CICLE, specially developed to disentangle the ICL from the light of galaxies and measure the ICL fraction. We measured the ICL fraction in three broad-band optical filters, F435W, F606W, and F814W, without assuming any prior hypothesis about the ICL physical properties or morphology. The results obtained from the ICL fraction vary between similar to 7-25 per cent, and similar to 3-22 per cent for both A370 and AS1063, respectively, which are consistent with theoretical predictions for the total amount of ICL obtained by ICL formation and evolution simulations. We found enhanced ICL fractions in the intermediate filter F606W for both clusters and we suggest that this is due to the presence of an excess of younger/lower metallicity stars in the ICL compared to the cluster galaxies. We conclude that both Abell 370 and Abell S1063 are merging systems since they exhibit a similar feature as merging CLASH and Frontier Fields clusters sub-sample previously analysed. We compare these results to the dynamical indicators obtained through different methods and we reinforce the use of ICL as a new and independent method to determine the dynamical state of clusters of galaxies.

Automated summary

In this study, we analysed the contribution of intracluster light (ICL) to the total luminosity of two massive galaxy clusters observed by the Hubble Space Telescope. We developed an algorithm called CICLE to separate the ICL from the light of galaxies and measure the ICL fraction. The results showed that the ICL fraction varied between 7-25% for Abell 370 and 3-22% for Abell S1063, consistent with theoretical predictions. We also found an enhanced ICL fraction in the intermediate filter F606W, indicating the presence of younger/lower metallicity stars in the ICL compared to the cluster galaxies. Based on these findings, we concluded that both Abell 370 and Abell S1063 are merging systems.