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

¹ Theoretical Physics Department, CERN, Geneva 23, 1211, Switzerland
² L’Ecole Polytechnique Federale de Lausanne, 1015 Lausanne, Switzerland
³ Institute Lorentz, Leiden University, Niels Bohrweg 2, Leiden 2333 CA, The Netherlands
⁴ APC, Universite Paris Diderot, CNRS/IN2P3, CEA/IRFU, France
e-mail: alexander.korochkin@apc.in2p3.fr
⁵ Institute for Nuclear Research of the Russian Academy of Sciences, 60th October Anniversary St. 7a, 117312 Moscow, Russia
⁶ Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia
⁷ Astronomy Department, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
⁸ National Research Nuclear University MEPhI, 115409 Moscow, Russia
⁹ Institute of High Energy Physics, Austrian Academy of Sciences, Nikolsdorfergasse 18, 1050 Vienna, Austria

Received: 19 June 2021
Accepted: 23 October 2021

Abstract

Aims. Intergalactic magnetic fields in the voids of the large-scale structure can be probed via measurements of secondary γ-ray emission from γ-ray interactions with extragalactic background light. Lower bounds on the magnetic field in the voids were derived from the nondetection of this emission. It is not clear a priori what kind of magnetic field is responsible for the suppression of the secondary γ-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.

Methods. We used IllustrisTNG cosmological simulations to study the effect of magnetized galactic wind bubbles on the secondary γ-ray flux.

Results. We show that within the IllustrisTNG model of baryonic feedback, galactic wind bubbles typically provide energy-independent secondary flux suppression at a 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 the special case when the primary γ-ray source has a hard intrinsic γ-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.