Theoretical Predictions of Colors and Metallicity of the Intra-Cluster Light
We study colors and metallicities of the Brightest Cluster Galaxies (BCGs) and Intra-Cluster Light (ICL) in galaxy groups and clusters, as predicted by a semi-analytic model of galaxy formation, coupled with a set of high-resolution N-body simulations. The model assumes stellar stripping and violent relaxation processes during galaxy mergers to be the main channels for the formation of the ICL. We find that BCGs are more metal-rich and redder than the ICL, at all redshifts since the ICL starts to form ($z\sim 1$). In good agreement with several observed data, our model predicts negative radial metallicity and color gradients in the BCG+ICL system. By comparing the typical colors of the ICL with those of satellite galaxies, we find that mass and metals in the ICL come from galaxies of different mass, depending on the redshift. Stripping of low mass galaxies, $9<\log M_* <10$, is the most important contributor in the early stage of the ICL formation, but the bulk of the mass/metals contents are given by intermediate/massive galaxies, $10<\log M_* <11$, at lower redshift. Our analysis supports the idea that stellar stripping is more important than galaxy mergers in building-up the ICL, and highlights the importance of colors/metallicity measurements for understanding the formation and evolution of the ICL.