The origin of the intracluster light in The Three Hundred simulations

¹ Departamento de Física Teórica, Módulo 15, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
² Departamento de Astrofísica, Universidad de La Laguna, Av. Astrofísico Francisco Sanchez s/n, 38206 La Laguna, Tenerife, Spain
³ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁴ Centro de Investigación Avanzada en Física Fundamental (CIAFF), Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
⁵ International Centre for Radio Astronomy Research, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia
⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷ Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
⁸ Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
⁹ Centre for Astrophysics & Supercomputing, Swinburne University of Technology, 1 Alfred St, Hawthorn, VIC 3122, Australia
¹⁰ ARC Centre of Excellence for Dark Matter Particle Physics (CDM), Melbourne, Australia
¹¹ School of Physics & Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
¹² INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, I34131 Trieste, Italy
¹³ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, 34151 Trieste, Italy
¹⁴ Department of Physics, University of Michigan, 450 Church St, Ann Arbor, MI 48109, USA
¹⁵ Instituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), CC 67, Suc. 28, 1428 Buenos Aires, Argentina

^⋆ Corresponding author: ana.contreras@iac.es

Received: 24 February 2025
Accepted: 17 September 2025

Abstract

We investigated the origin and formation mechanisms of the intracluster light (ICL) in THE THREE HUNDRED simulations, a set of 324 hydrodynamically resimulated massive galaxy clusters. The ICL, a diffuse component comprised of stars not bound to any individual galaxy, serves as a critical tracer of cluster formation and evolution. Using two implementations of hydrodynamics, GADGET-X and GIZMO-SIMBA, we identified the stellar particles that constitute the ICL at z = 0 and traced them back in time to the moments when they were formed and accreted into the ICL. Our analysis reveals that, across our 324 clusters, half of the present-day ICL mass is typically in place between z ∼ 0.2 and 0.5. The main ICL formation channel is the stripping of stars from subhalos after their infall into the host cluster. Within this channel, 65−80% of the ICL comes from objects with stellar (infall) masses above 10¹¹ M_⊙, corresponding to massive galaxies, groups and clusters. When we also consider the ratio of the infalling halo to the total cluster mass, we see that a median of 35% of the mass is brought in major merger events, although the percentage varies significantly across clusters (15−55%). Additional contributions come from minor mergers (25−35%) and smooth accretion (20−50%). The infall redshift of the primary contributors is generally below z ≤ 1, with smaller fractions arriving at redshifts between 1 and 2. Regarding other formation channels, we find minor contributions from stars formed in subhalos after their infall and stars stripped while their contributing halo remains outside the host cluster (and can eventually fall inside or stay outside). Finally, for our two sets of simulations, we find medians of 12 (GADGET-X) and 2 (GIZMO-SIMBA) percent of the ICL mass formed in situ, i.e. directly as part of the diffuse component. However, this component can be attributed to stripping of gas in high-velocity infalling satellite galaxies.