The gamma-ray emission of Ultra-fast Outflows

Massive black holes at the centers of galaxies can launch powerful wide-angle winds, which if sustained over time can unbind the gas from the stellar bulges of galaxies. Propagating through the galaxy, the wind should interact with the interstellar medium creating a strong shock, similar to those observed in supernovae explosions, which is able to accelerate charged particles to high energies. Here we report the Fermi Large Area Telescope detection of gamma-ray emission from these shocks in a small sample of galaxies exhibiting ultra-fast outflows. The detection implies that energetic black-hole winds transfer ~0.04 % of their mechanical power to gamma rays and that the gamma-ray emission may represent the onset of the wind-host interaction.