Clusters Have Edges: The Projected Phase SpaceStructure of SDSS redMaPPer Clusters. (arXiv:2003.11555v1 [astro-ph.CO])

Clusters Have Edges: The Projected Phase SpaceStructure of SDSS redMaPPer Clusters. (arXiv:2003.11555v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Tomooka_P/0/1/0/all/0/1">Paxton Tomooka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rozo_E/0/1/0/all/0/1">Eduardo Rozo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wagoner_E/0/1/0/all/0/1">Erika L. Wagoner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aung_H/0/1/0/all/0/1">Han Aung</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nagai_D/0/1/0/all/0/1">Daisuke Nagai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Safonova_S/0/1/0/all/0/1">Sasha Safonova</a>

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 $R_{rm edge} approx 2.2R_{rm{lambda}}$, where
$R_{rm{lambda}}$ is the cluster radius assigned by redMaPPer. We refer to
$R_{rm edge}$ 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 $R_{rm edge}$ 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.

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 $R_{rm edge} approx 2.2R_{rm{lambda}}$, where
$R_{rm{lambda}}$ is the cluster radius assigned by redMaPPer. We refer to
$R_{rm edge}$ 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 $R_{rm edge}$ 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.

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