Inner caustics of cold dark matter halos

Aravind Natarajan and Pierre Sikivie
Phys. Rev. D 73, 023510 – Published 19 January 2006

Abstract

We prove that a flow of cold collisionless particles from all directions in and out of a region necessarily forms a caustic. A corollary is that, in cold dark matter cosmology, galactic halos have inner caustics in addition to the more obvious outer caustics. The outer caustics are fold catastrophes located on topological spheres surrounding the galaxy. To obtain the catastrophe structure of the inner caustics, we simulate the infall of cold collisionless particles in a fixed gravitational potential. The structure of inner caustics depends on the angular momentum distribution of the infalling particles. We confirm a previous result that the inner caustic is a “tricusp ring” when the initial velocity field is dominated by net overall rotation. A tricusp ring is a closed tube whose cross section is a section of an elliptic umbilic catastrophe. However, tidal torque theory predicts that the initial velocity field is irrotational. For irrotational initial velocity fields, we find the inner caustic to have a tentlike structure which we describe in detail in terms of the known catastrophes. We also show how the tent caustic transforms into a tricusp ring when a rotational component is added to the initial velocity field.

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  • Received 26 October 2005

DOI:https://doi.org/10.1103/PhysRevD.73.023510

©2006 American Physical Society

Authors & Affiliations

Aravind Natarajan2 and Pierre Sikivie1,2

  • 1School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540, USA
  • 2Institute for Fundamental Theory, Department of Physics, University of Florida, Gainesville, Florida 32611-8440, USA

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Issue

Vol. 73, Iss. 2 — 15 January 2006

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