Intracluster light in the infall region of simulated protoclusters of galaxies

Abstract

Intracluster light (ICL) is a diffuse stellar component in galaxy clusters, made of stars following the potential of the cluster. Despite its potential to unveil the accretion history of clusters, the ICL in protoclusters remains poorly understood in simulations and observations. We analyse protoclusters in TNG-Cluster and Manhattan Suite simulations to investigate when ICL forms, its host progenitors, and environments where it forms. We find a considerable amount of ICL in the infall region of protoclusters at 2<z<4, ranging from $\rm 0.1\times10^{11}$<$M_{*}/M_{\odot}$<$3\times10^{11}$. ICL star formation in protoclusters peaks at 3<z<4, with stars formed in the main halo forming earlier than those born in the infall regions. We find that $74.2_{-1.7}^{+1.7}\%$ of ICL stars in TNG-Cluster and $69.2_{-3.7}^{+3.6}\%$ in Manhattan Suite were stripped from galaxies within the main halo. However, most ICL stars in protoclusters at z=2 formed in the infall region, accounting for $57.6_{-1.6}^{+1.7}\%$ and $55.6_{-2.3}^{+2.3}\%$ in TNG-Cluster and Manhattan Suite, respectively. By the time the ICL stars are stripped, their host galaxies are 3-4 times more massive than the galaxies in which the stars originally formed, implying growth of the progenitor galaxies and/or accretion of the stars onto more massive galaxies prior to stripping. The ICL stellar masses measured in simulations agree with observations at z$\leq$2. Our findings highlight the importance of investigating the diffuse light in the outer regions of protoclusters to constrain the formation and assembly of the ICL and galaxy clusters.