Early Starbursts and Magnetic Field Generation in Galaxy Clusters

Abstract

We propose a mechanism for the early generation of the mean intracluster magnetic field in terms of magnetized galactic winds. These winds are the result of starburst phases of the cluster galaxies, assumed to produce the predominant population of early-type galaxies in mergers of gas-rich progenitors. After further cluster contraction, typical field strengths are 10-7 G. This estimate may increase to the level of 10-6 G if more extreme galactic parameters and subsequent shear amplification of the field are considered. The topology of the field is one of almost unconnected wind bubbles with Parker-type spiral field configurations over scales of the distance between galaxies. Further cluster accretion, which continues chaotically in space and time up to the present, will perturb these "large-scale" mean fields on smaller or at best comparable spatial scales. The small-scale fields in the resulting turbulent fluctuation spectrum should be able to confine relativistic particles over times longer than the age of the universe. The nonthermal particle content of galaxy clusters should therefore also have a "cosmological" hadronic component generated during the early starburst phase of the member galaxies. Already by itself it implies a nonthermal energy fraction of about 10% for the intracluster gas that should then be detectable by future γ-ray telescopes.