Testing the Dark Matter Annihilation Model for the WMAP Haze

TL;DR

This paper evaluates whether the WMAP haze is caused by dark matter annihilation or astrophysical sources, proposing observational signatures to distinguish between these scenarios.

Contribution

It compares dark matter and astrophysical models for the haze, highlighting spectral and spatial signatures that can be used to identify the true origin.

Findings

Dark matter models predict a very hard, angle-independent spectrum.

Astrophysical sources like supernovae can produce similar emissions within constraints.

Spectral index trends as a function of angle can differentiate models.

Abstract

Analyses have found a "haze" of anomalous microwave emission surrounding the Galactic Center in the WMAP sky maps. A recent study using Fermi data detected a similar haze in the gamma-ray. Several studies have modeled these hazes as radiation from the leptonic byproducts of dark matter annihilations, and arguably no convincing astrophysical alternative has been suggested. We discuss the characteristics of astrophysical cosmic ray sources that could potentially explain this microwave and gamma-ray emission. The most promising astrophysical scenarios involve cosmic ray sources that are clustered such that many fall within ~1 kpc of the Galactic Center. For example, we show that several hundred Galactic Center supernovae in the last million years plus a diffusion-hardened electron spectrum may be consistent with present constraints on this emission. Alternatively, it could be due to a burst of activity probably associated with Sagittarius A* occurring ~1 Myr ago and producing >10^51 erg in cosmic ray electrons. Different models predict different trends for the spectral index of the microwave and gamma-ray spectrum as a function of angle from the Galactic Center that should be robust to cosmic ray propagation uncertainties. In particular, if the haze is from dark matter annihilations, it should have a very hard microwave and gamma-ray spectrum for which the spectral shape does not change significantly with angle, which we argue would be difficult to achieve with any astrophysical mechanism. Observations with the Planck and Fermi satellites can distinguish between viable haze models using these signatures.