The Fermi gamma-ray haze from dark matter annihilations and anisotropic diffusion

Recent full-sky maps of the Galaxy from the Fermi Gamma-Ray Space Telescope have revealed a diffuse component of emission toward the Galactic center and extending up to roughly ± 50° in latitude. This Fermi "haze" is the inverse Compton emission generated by the same electrons that generate the microwave synchrotron haze at Wilkinson Microwave Anisotropy Probe wavelengths. The gamma-ray haze has two distinct characteristics: the spectrum is significantly harder than emission elsewhere in the Galaxy and the morphology is elongated in latitude with respect to longitude with an axis ratio of ≈ 2. If these electrons are generated through annihilations of dark matter (DM) particles in the Galactic halo, this morphology is difficult to realize with a standard spherical halo and isotropic cosmic-ray (CR) diffusion. However, we show that anisotropic diffusion along ordered magnetic field lines toward the center of the Galaxy coupled with a prolate DM halo can easily yield the required morphology without making unrealistic assumptions about diffusion parameters. Furthermore, a Sommerfeld enhancement to the self-annihilation cross-section of ∼ 30 yields a good fit to the morphology, amplitude, and spectrum of both the gamma-ray and microwave haze. The model is also consistent with local CR measurements as well as cosmic microwave background constraints.