Detection of the Galactic haze with Planck (Planck Collaboration)

Vol. 554
In section 5. Galactic structure, stellar clusters and populations

Planck intermediate results. IX. Detection of the Galactic haze with Planck

by Planck Collaboration A&A 554, A139

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In the course of its all-sky survey, the final results of which will be reported in an upcoming special issue of A&A, the Planck collaboration studied the Galactic haze between 20 and 100 GHz. There are two components to the diffuse emission, one that is consistent with a cosmic-ray component of synchrotron-emitting electrons and another much more energetic population that is responsible for the structures discovered by the Fermi/LAT observations at high Galactic latitude toward the Galactic center. This more confined - yet still diffuse - emission, which correlates spatially with the Fermi bubbles at GeV energies discovered by the Fermi/LAT, appears to be caused by synchrotron emission from electrons with a harder spectral energy distribution than anywhere else in the Milky Way. Other possible sources, rapidly spinning dust grains or thermal bremsstrahlung, are ruled out by the spectrum. Perhaps the most remarkable result is that the 30 GHz emission from the Galactic southern hemisphere appears to coincide precisely with the extent of the Fermi 2-5 GHz haze, even to the extent of showing the same edge at a latitude of about -50 degrees, about 17 degrees from the bubble's center as determined by Fermi.