The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays

TL;DR

The paper explains the Fermi Bubbles as giant reservoirs of relic cosmic rays from long-term star formation activity in the Galactic center, accounting for multi-wavelength observations.

Contribution

It presents a novel explanation linking the Fermi Bubbles to ancient cosmic ray populations from prolonged star formation in the Galactic center.

Findings

Fermi Bubbles are consistent with relic cosmic ray protons and ions.

The bubbles' gamma-ray emission is explained by long-lived cosmic ray populations.

The model accounts for multi-wavelength observations from gamma-ray to X-ray.

Abstract

Recently evidence has emerged for enormous features in the gamma-ray sky observed by the Fermi-LAT instrument: bilateral `bubbles' of emission centered on the core of the Galaxy and extending to around 10 kpc above and below the Galactic plane. These structures are coincident with a non-thermal microwave `haze' found in WMAP data and an extended region of X-ray emission detected by ROSAT. The bubbles' gamma-ray emission is characterised by a hard and relatively uniform spectrum, relatively uniform intensity, and an overall luminosity ~4 x 10^37 erg/s, around one order of magnitude larger than their microwave luminosity while more than order of magnitude less than their X-ray luminosity. Here we show that the bubbles are naturally explained as due to a population of relic cosmic ray protons and heavier ions injected by processes associated with extremely long timescale (>~8 Gyr) and high areal density star-formation in the Galactic center.