Account of the baryonic feedback effect in gamma-ray measurements of intergalactic magnetic fields

Abstract

Intergalactic magnetic fields in the voids of the large-scale structure can be probed via measurements of secondary gamma-ray emission from gamma-ray interactions with extragalactic background light. Lower bounds on the magnetic field in the voids were derived from the non-detection of this emission. It is not clear a priori what kind of magnetic field is responsible for the suppression of the secondary gamma-ray flux: a cosmological magnetic field that might be filling the voids or the field spread by galactic winds driven by star formation and active galactic nuclei. We used IllustrisTNG cosmological simulations to study the effect of magnetized galactic wind bubbles on the secondary gamma-ray flux. We show that within the IllustrisTNG model of baryonic feedback, the galactic wind bubbles typically provide energy-independent secondary flux suppression at the level of about 10%. The observed flux suppression effect has to be due to the cosmological magnetic field in the voids. This might not be the case for a special case when the primary gamma-ray source has a hard intrinsic gamma-ray spectrum that peaks in the energy range above 50 TeV. In this case, the observational data may be strongly affected by the magnetized bubble that is blown by the source host galaxy.