The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze

TL;DR

The paper identifies a gamma-ray counterpart to the microwave haze in the inner Galaxy, supporting the synchrotron origin of the microwave signal and revealing a hard electron population through Fermi observations.

Contribution

It presents the first detailed analysis linking the gamma-ray haze to the microwave haze, using spatial templates and revealing a hard electron spectrum in the Galactic center.

Findings

Detection of a gamma-ray excess with a hard spectrum near the Galactic center.

Morphology and spectrum consistent with inverse Compton scattering from electrons causing the microwave haze.

Full sky Fermi maps provided for further research.

Abstract

The Fermi Gamma-Ray Space Telescope reveals a diffuse inverse Compton signal in the inner Galaxy with a similar spatial morphology to the microwave haze observed by WMAP, supporting the synchrotron interpretation of the microwave signal. Using spatial templates, we regress out pi0 gammas, as well as IC and bremsstrahlung components associated with known soft-synchrotron counterparts. We find a significant gamma-ray excess towards the Galactic center with a spectrum that is significantly harder than other sky components and is most consistent with IC from a hard population of electrons. The morphology and spectrum are consistent with it being the IC counterpart to the electrons which generate the microwave haze seen at WMAP frequencies. In addition, the implied electron spectrum is hard; electrons accelerated in supernova shocks in the disk which then diffuse a few kpc to the haze region would have a softer spectrum. We describe the full sky Fermi maps used in this analysis and make them available for download.