Cosmic ray transport in starburst galaxies and possible observables

Abstract

The nuclei of starburst galaxies are unique sources of high-energy radiation where ideal condi-tions for cosmic ray acceleration and confinement might be achieved. We investigate the con-ditions for effective cosmic ray confinement by modelling the transport accounting for diffusionand advection, and we study the implications of such confinement in terms of multifrequencyemission and production of high-energy neutrinos. Both primary and secondary electrons, aswell as electron-positron pairs produced by gamma ray absorption inside these regions are takeninto account. Electrons and positrons produced as secondary products of hadronic interactionsare found to be responsible for most of the emission of leptonic origin. In particular, secondaryelectrons produce an extended synchrotron emission of hard X-rays that represent a remarkablesignature of hadronic processes, potentially accessible to current and future observations in theX-ray band. We also apply for the first time our detailed model to study the starburst contributionto the diffuse gamma-ray and neutrino fluxes observed by Fermi-LAT and IceCube. In order toassess such contribution we adopt a redshift number density of starburst-like objects based on theinfrared luminosity function inferred by Herschel observations and we take into account the effectof the electromagnetic cascade in the intergalactic medium.