Clusters have edges: The projected phase-space structure of SDSS redMaPPer clusters

Paxton Tomooka, Eduardo Rozo, Erika L. Wagoner, Han Aung, Daisuke Nagai, Sasha Safonova

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


We study the distribution of line-of-sight velocities of galaxies in the vicinity of Sloan Digital Sky Survey (SDSS) red-sequence Matched-filter Probabilistic Percolation (redMaPPer) galaxy clusters. Based on their velocities, galaxies can be split into two categories: galaxies that are dynamically associated with the cluster, and random line-of-sight projections. Both the fraction of galaxies associated with the galaxy clusters, and the velocity dispersion of the same, exhibit a sharp feature as a function of radius. The feature occurs at a radial scale Redge ≈ 2.2Rλ, where Rλ is the cluster radius assigned by redMaPPer. We refer to Redge as the 'edge radius'. These results are naturally explained by a model that further splits the galaxies dynamically associated with a galaxy cluster into a component of galaxies orbiting the halo and an infalling galaxy component. The edge radius Redge constitutes a true 'cluster edge', in the sense that no orbiting structures exist past this radius. A companion paper tests whether the 'halo edge' hypothesis holds when investigating the full three-dimensional phase-space distribution of dark matter substructures in numerical simulations, and demonstrates that this radius coincides with a suitably defined splashback radius.

Original languageEnglish (US)
Pages (from-to)1291-1299
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - Nov 1 2020


  • Dark matter
  • Galaxies: clusters: general
  • Galaxies: haloes
  • Large-scale structure of Universe

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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