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


We study the distribution of line-of-sight velocities of galaxies in the vicinity of SDSS 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 (Aung et al. 2020) 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)
JournalUnknown Journal
StatePublished - Mar 25 2020

ASJC Scopus subject areas

  • General

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