Counting Dark Sub-halos with Star Stream Gaps

TL;DR

This paper investigates dark matter sub-halos by analyzing star stream gaps, finding good agreement with LCDM predictions and estimating a large population of sub-halos based on observed stream features.

Contribution

It introduces a method to count dark matter sub-halos through star stream gaps and compares observations with LCDM predictions, supporting the dark matter paradigm.

Findings

Good agreement between observed stream gaps and LCDM predictions

Narrow streams imply about 10^5 sub-halos above 10^5 solar masses

Stream gap rates depend on stream width and sub-halo properties

Abstract

The Cold Dark Matter paradigm predicts vast numbers of dark matter sub-halos to be orbiting in galactic halos. The sub-halos are detectable through the gaps they create gaps in stellar streams. The gap-rate is an integral over the density of sub-halos, their mass function, velocity distribution and the dynamical age of the stream. The rate of visible gap creation is a function of the width of the stream. The available data for four streams: the NW stream of M31, the Pal~5 stream, the Orphan Stream and the Eastern Banded Structure, are compared to the LCDM predicted relation. We find a remarkably good agreement, although there remains much to be done to improve the quality of the result. The narrower streams require that there is a total population of order 10^5 sub-halos above 10^5 M_sun to create the gaps.