From Stellar Halos to Intracluster Light: the physics of the Intra-Halo Stellar Component in cosmological hydrodynamical simulations.
2019
We study the Intra-Halo Stellar Component (IHSC) of Milky Way-mass systems up to galaxy clusters in the Horizon-AGN cosmological hydrodynamical simulation. We identify the IHSC using an improved phase-space galaxy finder algorithm which provides an adaptive, physically motivated and shape-independent definition of this stellar component, that can be applied to halos of arbitrary masses. We explore the IHSC mass fraction-total halo's stellar mass, $f_{M*,IHSC}-M*$, relation and the physical drivers of its scatter. We find that on average the $f_{M*,IHSC}$ increases with $M_{*,tot}$, with the scatter decreasing strongly with mass from 2 dex at $M_{*,tot}\sim10^{11}M_\odot$ to 0.3 dex at group masses. At high masses, $M_{*,tot}>10^{11.5}M_\odot$, $f_{M*,IHSC}$ increases with the number of substructures, and with the mass ratio between the central galaxy and largest satellite, at fixed $M_{*,tot}$. From mid-size groups and systems below $M_{*,tot} 1), while the high $f_{M*,IHSC}$ population displays a much more active merger history. In the case of massive groups and galaxy clusters, $M_{*,tot}>10^{12}M_\odot$, a fraction $f_{M*,IHSC}\sim$10-20% is reached at $z\sim1$ and then they evolve across lines of constant $f_{M*,IHSC}$ modulo some small perturbations. Because of the limited simulation's volume, the latter is only tentative and requires a larger sample of simulated galaxy clusters to confirm.
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