Decaying dark matter: the case for a deep X-ray observation of Draco

TL;DR

This paper predicts the X-ray flux from decaying dark matter in the Milky Way and M31 using simulations, and proposes a deep X-ray observation of Draco to test the dark matter decay hypothesis at 3.5 keV.

Contribution

It provides simulation-based flux predictions and demonstrates that a 1.3 Msec XMM-Newton observation of Draco can confirm or refute dark matter decay at 3.5 keV.

Findings

M31 and Galactic center detections are compatible with a decay time of ~10^28 seconds.

Deep observations of Draco can detect or rule out dark matter decay at 3.5 keV with 95% confidence.

Predicted flux levels support the feasibility of testing dark matter decay with current X-ray telescopes.

Abstract

Recent studies of M31, the Galactic centre, and galaxy clusters have made tentative detections of an X-ray line at ~3.5 keV that could be produced by decaying dark matter. We use high resolution simulations of the Aquarius project to predict the likely amplitude of the X-ray decay flux observed in the GC relative to that observed in M31, and also of the GC relative to other parts of the Milky Way halo and to dwarf spheroidal galaxies. We show that the reported detections from M31 and Andromeda are compatible with each other, and with upper limits arising from high galactic latitude observations, and imply a decay time {\tau} ~10^28 seconds. We argue that this interpretation can be tested with deep observations of dwarf spheroidal galaxies: in 95 per cent of our mock observations, a 1.3 Msec pointed observation of Draco with XMM-Newton will enable us to discover or rule out at the 3{\sigma} level an X-ray feature from dark matter decay at 3.5 keV, for decay times {\tau} < 0.8x10^28 sec.