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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

Disentangling the assembly of the central and diffuse stellar components in galaxy clusters through dynamical friction and tidal stripping

  • Frazer R Pearce1
  • Steven P Bamford1
  • Garreth Martin1
  • Yannick M Bahé1,2
  • Harley J Brown1
  • Madeline Butler1
  • Ana Contreras-Santos3,4,5
  • Weiguang Cui5,6,7
  • Nina Hatch1
  • Alexander Knebe5,6,8
8 affiliations
  1. 1School of Physics and Astronomy, University of Nottingham , Nottingham NG7 2RD ,
  2. 2Laboratoire d’Astrophysique, École Polytechnique Fédérale de Lausanne (EPFL) , Observatoire de Sauverny, CH-1290 Versoix ,
  3. 3Departamento de Astrofísica, Universidad de La Laguna , Av. Astrofísico Francisco Sanchez s/n, E-38206 La Laguna, Tenerife ,
  4. 4Instituto de Astrofísica de Canarias , C/Vía Láctea s/n, E-38205 La Laguna, Tenerife ,
  5. 5Departamento de Física Teórica , Módulo 15, Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid ,
  6. 6Centro de Investigación Avanzada en Física Fundamental (CIAFF), Facultad de Ciencias, Universidad Autónoma de Madrid , E-28049 Madrid ,
  7. 7Institute for Astronomy , Royal Observatory, Edinburgh EH9 3HJ ,
  8. 8International Centre for Radio Astronomy Research, University of Western Australia , 35 Stirling Highway, Crawley, Western Australia 6009 ,
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Abstract

In galaxy clusters, it is common to conceptually distinguish the central, brightest cluster galaxy (BCG) from the more diffuse intracluster light (ICL). So far, however, this distinction has lacked a clear physical basis, confusing both theoretical and observational studies. We address this by presenting a dynamically motivated definition of the two stellar components, evaluated using cluster zoom simulations from the three hundred project. We start with a motivational hindcasting approach, robustly tracing stars from the centres of 107 present-day clusters back through the merger hierarchy. We find that the majority of the final BCG stellar mass is typically contributed by the central galaxies of only 3–5 progenitor haloes. Most accreted galaxies contribute no stars to the BCG, instead surviving as satellites or depositing stellar material throughout the cluster. This naturally leads to a definition of the BCG stellar population as originating from the central galaxies of the most massive infalling systems. These are delivered to the cluster centre via efficient dynamical friction and subsequently undergo violent relaxation. The ICL arises from the complementary population of stars tidally stripped from the outskirts of all infalling systems. We therefore develop a forecasting method, identifying stars in the BCG and ICL via the dynamical fates of their originating stellar systems. Applying this to 261 clusters, we find the resulting components remain spatially interleaved, but occupy distinct regions of phase space. Our physically defined BCG matches conventional aperture-based selections with high completeness, while providing a direct interpretation in terms of hierarchical assembly.

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Cite

BibTeXRIS
BibTeX
@article{pearce2026disentangling,
  title = {{Disentangling the assembly of the central and diffuse stellar components in galaxy clusters through dynamical friction and tidal stripping}},
  author = {Frazer R Pearce and Steven P Bamford and Garreth Martin and Yannick M Bahé and Harley J Brown and Madeline Butler and Ana Contreras-Santos and Weiguang Cui and Nina Hatch and Alexander Knebe},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag1912},
  url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1912/8907356},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Disentangling the assembly of the central and diffuse stellar components in galaxy clusters through dynamical friction and tidal stripping
AU  - Frazer R Pearce
AU  - Steven P Bamford
AU  - Garreth Martin
AU  - Yannick M Bahé
AU  - Harley J Brown
AU  - Madeline Butler
AU  - Ana Contreras-Santos
AU  - Weiguang Cui
AU  - Nina Hatch
AU  - Alexander Knebe
PY  - 2026
DA  - 2026/10/10
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag1912
UR  - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1912/8907356
AB  - In galaxy clusters, it is common to conceptually distinguish the central, brightest cluster galaxy (BCG) from the more diffuse intracluster light (ICL). So far, however, this distinction has lacked a clear physical basis, confusing both theoretical and observational studies. We address this by presenting a dynamically motivated definition of the two stellar components, evaluated using cluster zoom simulations from the three hundred project. We start with a motivational hindcasting approach, robustly tracing stars from the centres of 107 present-day clusters back through the merger hierarchy. We find that the majority of the final BCG stellar mass is typically contributed by the central galaxies of only 3–5 progenitor haloes. Most accreted galaxies contribute no stars to the BCG, instead surviving as satellites or depositing stellar material throughout the cluster. This naturally leads to a definition of the BCG stellar population as originating from the central galaxies of the most massive infalling systems. These are delivered to the cluster centre via efficient dynamical friction and subsequently undergo violent relaxation. The ICL arises from the complementary population of stars tidally stripped from the outskirts of all infalling systems. We therefore develop a forecasting method, identifying stars in the BCG and ICL via the dynamical fates of their originating stellar systems. Applying this to 261 clusters, we find the resulting components remain spatially interleaved, but occupy distinct regions of phase space. Our physically defined BCG matches conventional aperture-based selections with high completeness, while providing a direct interpretation in terms of hierarchical assembly.
SN  - 0035-8711
SN  - 1365-2966
ER  -