Tracing the Formation History of Intrahalo Light with Horizon Run 5

Abstract We investigate the formation history of intrahalo light (IHL) using the high-resolution (∼1 kpc), large-scale (∼1 Gpc) cosmological hydrodynamical simulation Horizon Run 5 (HR5). IHL particles are identified by carefully considering both their binding energies and positions with respect to the tidal radii of individual galaxies. By analyzing more than 1200 galaxy groups and clusters with ≳10 13 M ⊙ and tracing their individual IHL particles back in time, we classify the origin of each IHL particle at each epoch, based on the status of the originating galaxy, into one of three categories: brightest halo galaxy (BHG) formation/merger, satellite galaxy stripping, and preprocessing. Our study reveals that IHL production through BHG formation/merger is the predominant production channel, contributing over 60% of the total IHL mass across all redshifts. The second most significant IHL production channel is preprocessing, providing more than 20% in the final HR5 snapshot. Stripping is negligible at z > 4 but becomes gradually more important as the halos mature at z < 4. Finally, we verify that the IHL production through the disruption of dwarf galaxies and in situ formation is negligible, contributing less than ∼3% and ∼0.5% to the total IHL production, respectively.