Skip to content
DraconiticResearch
Search Sources API
189,105 studies31 sourcesUpdated 34 min ago
Peer-reviewedCC BY 4.0The Astrophysical Journal

Quantifying the Dominance and Emergence of Brightest Cluster Galaxies in SPT and Planck Clusters: A Novel Application of the Gini Index

  • Katiya Fosdick1
  • Michael McDonald1,2
  • Gourav Khullar3
  • Michael D. Gladders4
  • Boris Häußler5
  • Cian Roche1
  • Lindsey E. Bleem4,6
  • Benjamin Floyd7
  • Raven Gassis8
  • Sebastian Grandis9
  • Arnab Sarkar2,10
  • Veronica Strazzullo11,12
1 more authors
  • Taweewat Somboonpanyakul13
13 affiliations
  1. 1Massachusetts Institute of Technology
  2. 2MIT Kavli Institute for Astrophysics and Space Research
  3. 3University of Washington
  4. 4University of Chicago
  5. 5European Southern Observatory
  6. 6High-Energy Physics Division
  7. 7University of Portsmouth
  8. 8University of Cincinnati
  9. 9Universität Innsbruck
  10. 10University of Arkansas
  11. 11INAF–Astronomical Observatory of Trieste
  12. 12IFPU–Institute for Fundamental Physics of the Universe
  13. 13Chulalongkorn University
Open at sourcePDFDOICite

Abstract

We introduce the Gini index ( G ) as a metric for studying the emergence of brightest cluster galaxies (BCGs) by quantifying the disparity in the light distribution of galaxy cluster cores. The Gini index collapses the skewness of the bright-end luminosity function to a single statistic, and provides a measure for the light dominance of the BCG over other cluster members that is more robust than the magnitude gap. We argue that the Gini index is far less sensitive to short-term changes in the cluster dynamical state than the magnitude gap and solves its known degeneracies by taking the entire cluster membership into account, making G a more sensitive metric to long-term BCG assembly. We apply the magnitude gap and Gini index to a progenitor-selected sample of 92 South Pole Telescope- and Planck-selected cluster cores at 0 < z < 1 with corresponding Hubble Space Telescope F110W and F200LP and Sloan Digital Sky Survey g and r photometry. Based on both parametric and empirical tests, we find no statistical evidence for evolution in G or M 1,2 over 0 < z < 1, and find that BCGs have not grown significantly (2×) faster than the cluster population for z < 1 at 3 σ confidence. This implies that BCGs achieve dominance and establish defining properties early ( z > 1) in massive clusters. In general, we find that the Gini index is a valuable and relatively straightforward measurement, with well-controlled systematics, that could be applied to much larger samples to study BCG dominance and emergence.

Related

  1. More Numerous and Bluer: Companions of the Brightest Little Red Dots Differ from Control Galaxies at >3σ, Hinting at Synchronized Black Hole Seed Formation
    Fabio Pacucci, C. Megan Urry
    arXivPreprintarXiv licenceFull textCosmologyGalaxiesarXiv
  2. More Numerous and Bluer: Companions of the Brightest Little Red Dots Differ from Control Galaxies at > 3 σ , Hinting at Synchronized Black Hole Seed Formation
    Fabio Pacucci, C. Megan Urry
    The Astrophysical Journal LettersPeer-reviewedCC BY 4.0Full textGalaxiesCrossref
  3. Active galactic nucleus activity in brightest cluster galaxies at intermediate redshifts in Sunyaev-Zel'dovich--selected clusters
    N. Hatamkhani, R. E. Skelton, J. Delhaize +4
    arXivPreprintarXiv licenceFull textGalaxiesarXiv
  4. The star-forming past and quenching of brightest cluster galaxies in TNG-Cluster
    Sunna Gottschewski, Joey Braspenning, Annalisa Pillepich +2
    arXivPreprintCC BY 4.0Full textCosmologyGalaxiesarXiv
  5. Euclid: Disky titans - surprisingly high star formation activity and gas content in two brightest group galaxies at z~0.75
    F. Gentile, E. Daddi, D. Elbaz +166
    arXivPreprintCC BY 4.0Full textGalaxiesarXiv

Cite

BibTeXRIS
BibTeX
@article{fosdick2026quantifying,
  title = {{Quantifying the Dominance and Emergence of Brightest Cluster Galaxies in SPT and Planck Clusters: A Novel Application of the Gini Index}},
  author = {Katiya Fosdick and Michael McDonald and Gourav Khullar and Michael D. Gladders and Boris Häußler and Cian Roche and Lindsey E. Bleem and Benjamin Floyd and Raven Gassis and Sebastian Grandis and Arnab Sarkar and Veronica Strazzullo and Taweewat Somboonpanyakul},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = nov,
  doi = {10.3847/1538-4357/aea69f},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea69f},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Quantifying the Dominance and Emergence of Brightest Cluster Galaxies in SPT and Planck Clusters: A Novel Application of the Gini Index
AU  - Katiya Fosdick
AU  - Michael McDonald
AU  - Gourav Khullar
AU  - Michael D. Gladders
AU  - Boris Häußler
AU  - Cian Roche
AU  - Lindsey E. Bleem
AU  - Benjamin Floyd
AU  - Raven Gassis
AU  - Sebastian Grandis
AU  - Arnab Sarkar
AU  - Veronica Strazzullo
AU  - Taweewat Somboonpanyakul
PY  - 2026
DA  - 2026/11/02
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea69f
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea69f
AB  - We introduce the Gini index ( G ) as a metric for studying the emergence of brightest cluster galaxies (BCGs) by quantifying the disparity in the light distribution of galaxy cluster cores. The Gini index collapses the skewness of the bright-end luminosity function to a single statistic, and provides a measure for the light dominance of the BCG over other cluster members that is more robust than the magnitude gap. We argue that the Gini index is far less sensitive to short-term changes in the cluster dynamical state than the magnitude gap and solves its known degeneracies by taking the entire cluster membership into account, making G a more sensitive metric to long-term BCG assembly. We apply the magnitude gap and Gini index to a progenitor-selected sample of 92 South Pole Telescope- and Planck-selected cluster cores at 0 < z < 1 with corresponding Hubble Space Telescope F110W and F200LP and Sloan Digital Sky Survey g and r photometry. Based on both parametric and empirical tests, we find no statistical evidence for evolution in G or M 1,2 over 0 < z < 1, and find that BCGs have not grown significantly (2×) faster than the cluster population for z < 1 at 3 σ confidence. This implies that BCGs achieve dominance and establish defining properties early ( z > 1) in massive clusters. In general, we find that the Gini index is a valuable and relatively straightforward measurement, with well-controlled systematics, that could be applied to much larger samples to study BCG dominance and emergence.
SN  - 1538-4357
SN  - 0004-637X
ER  -