Can proper motions of dark-matter subhalos be detected?

TL;DR

This paper investigates the potential to detect proper motions of dark-matter subhalos via gamma-ray observations, concluding that current background limits restrict such detections to less than one nearby subhalo.

Contribution

It provides the first quantitative constraint on the detectability of dark-matter subhalo proper motions using gamma-ray data.

Findings

Proper motions of dark-matter subhalos are unlikely to be detectable with current gamma-ray background limits.

The number of nearby subhalos capable of proper motion detection is constrained to less than one.

Current gamma-ray observations do not support the detection of individual subhalo proper motions.

Abstract

One of the goals of NASA's Fermi Gamma-ray Space Telescope (formerly GLAST) will be detection of gamma rays from dark-matter annihilation in the Galactic halo. Theoretical arguments suggest that dark matter may be bound into subhalos with masses as small as 10^{-4}--10^2 Earth mass. If so, it may be possible to detect individual subhalos as point sources in the Fermi Telescope. It has further been argued that some of these point sources may exhibit proper motions. Here we show that upper limits to the diffuse gamma-ray background constrain the number of subhalos close enough to exhibit proper motions to be less than one.