The Dependence of Halo Clustering on Subhalo Anisotropy and Planarity

Abstract

We show that host cold dark matter (CDM) haloes cluster in a manner that depends upon the anisotropy and planarity of their subhaloes, indicating an environmental dependence to subhalo anisotropy and planarity. The spatial distributions of both satellite galaxies about central galaxies and subhaloes about host haloes have been subjects of interest for two decades. Important questions include the degree to which satellites are distributed anisotropically about their hosts or exhibit planarity as well as the degree to which this anisotropy depends on the environment of the system. We study the spatial distributions of subhaloes in a cosmological N-body simulation. We find that CDM subhaloes are distributed in a manner that is strongly anisotropic and planar, in agreement with prior work, though w e present this in a new way. The more novel result is that anisotropy has an environmental dependence. Systems with subhaloes that exhibit $\textit{less}$ ($\textit{more}$) anisotropy, $\textit{less}$ ($\textit{more}$) planarity, and reside $\textit{further}$ from ($\textit{closer}$ to) their host centres cluster more $\textit{strongly}$ ($\textit{weakly}$). Moreover, these clustering effects are not primarily the result of the correlation between subhalo anisotropy and/or planarity and another $\textit{single}$ halo property upon which clustering is already known to depend (e.g. concentration). This is a new and distinct effect. We discuss the impact of this result on the anisotropies of satellites as predict ed by CDM, its testability, and its possible relation to the anisotropies observed about the large galaxies of the Local Group. In an appendix, we clarify our construction of ellipsoidal mock halo catalogues.