A Unified Model of the Fermi Bubbles, Microwave Haze, and Polarized Radio Lobes: Reverse Shocks in the Galactic Center's Giant Outflows

Understand

The Galactic Center's giant outflows are manifest in three different, non-thermal phenomena: i) the hard-spectrum, \gamma-ray `Fermi Bubbles' emanating from the nucleus and extending to |b| ~ 50 degrees; ii) the hard-spectrum, total-intensity microwave (~ 20-40 GHz) `Haze' extending to |b| ~ 35 degrees in the lower reaches of the Fermi Bubbles; and iii) the steep spectrum, polarized, `S-PASS' radio (~ 2-20 GHz) Lobes that envelop the Bubbles and extend to |b| ~ 60 degrees.

• We find that the nuclear outflows inflate a genuine bubble in each Galactic hemisphere that has the classical structure, working outwards, of reverse shock, contact discontinuity, and forward shock.
• Expanding into the finite pressure of the halo and given appreciable cooling and gravitational losses, the contact discontinuity of each bubble is now expanding only very slowly.
• We find observational signatures in both hemispheres of giant, reverse shocks at heights of ~ 1 kpc above the nucleus; their presence ultimately explains all three of the non-thermal phenomena mentioned above.