A Last Look at the Microwave Haze/Bubbles with WMAP

TL;DR

This paper reviews WMAP's seven-year data on the microwave haze/bubbles, confirming their existence and characteristics, and discusses their possible origins in relation to gamma-ray observations and electron spectra.

Contribution

It provides a comprehensive analysis of WMAP data on the microwave haze/bubbles, comparing them with gamma-ray observations and discussing their spectral and spatial properties.

Findings

Haze is elongated in latitude, sharply cuts off above ~35 degrees at high latitudes.

Microwave and gamma-ray emissions are consistent with electron spectra but likely originate from different energy regions.

No significant polarization detected in the haze with WMAP data.

Abstract

The microwave "haze" was first discovered with the initial release of the full sky data from the Wilkinson Microwave Anisotropy Probe. It is diffuse emission towards the center of our Galaxy with spectral behavior that makes it difficult to categorize as any of the previously known emission mechanisms at those wavelengths. With now seven years of WMAP data publicly available, we have learned much about the nature of the haze, and with the release of data from the Fermi Gamma-Ray Space Telescope and the discovery of the gamma-ray haze/bubbles, we have had a spectacular confirmation of its existence at other wavelengths. As the WMAP mission winds down and the Planck mission prepares to release data, I take a last look at what WMAP has to tell us about the origin of this unique Galactic feature. Much like the gamma-rays, the microwave haze/bubbles is elongated in latitude with respect to longitude by a factor of roughly two, and at high latitudes, the microwave emission cuts off sharply above ~35 degrees (compared to ~50 degrees in the gammas). The hard spectrum of electrons required to generate the microwave synchrotron is consistent with that required to generate the gamma-ray emission via inverse Compton scattering, though it is likely that these signals result from distinct regions of the spectrum (~10 GeV for the microwaves, ~1 TeV for the gammas). While there is no evidence for significant haze polarization in the 7-year WMAP data, I demonstrate explicitly that it is unlikely such a signal would be detectable above the noise.