Evolution of velocity dispersion along cold collisionless flows

TL;DR

This paper investigates how velocity dispersion evolves in cold collisionless dark matter flows, especially near caustics, and presents methods to estimate their properties from potential dark matter detection signals.

Contribution

It introduces a technique to analyze the behavior of velocity dispersion near caustics in cold dark matter flows and applies it to predict and constrain flow properties.

Findings

Derived an upper limit on the energy dispersion of the Big Flow.

Provided a method to determine velocity dispersions from caustic sharpness.

Predicted dispersions in velocity components of dark matter flows.

Abstract

The infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behaviour of the velocity dispersion near caustics. The results are used to derive an upper limit on the energy dispersion of the Big Flow from the sharpness of its nearby caustic, and a prediction for the dispersions in its velocity components.