Sarah Recchia - Giant Cosmic-Ray Halos around M31 and the Milky Way

Friday 19 May 2023, 10:30 → 12:01 Europe/Berlin

Villa (SR5) (DESY)

In recent years, a  diffuse emission of 1–100 GeV gamma-rays has been detected from the direction of M31, extending up to 200 kpc from its center. The interpretation of  such  extended emission by the escape of cosmic rays produced in the galactic disk or in the galactic center is problematic and alternative explanations involving dark matter as a possible source  have been proposed in the literature.  Here we provide a critical evaluation of  a possible cosmic-ray origin (either leptonic or hadronic) of the gamma-ray emission  in the framework of nonstandard cosmic-ray propagation
scenarios or  in the case of  in situ particle acceleration in the galaxy’s halo. Correspondingly, the halo is powered by
the galaxy’s nuclear activity or by the accretion of intergalactic gas.  Intriguingly, if the formation of cosmic-ray halos around
galaxies is a common phenomenon, the interactions of cosmic-ray protons and nuclei with the circumgalactic gas surrounding the Milky Way could be responsible for the isotropic diffuse flux of neutrinos observed by IceCube.

Adromeda_Desy.pdf