Strong magnetic fields and cosmic rays in very young galaxies
University Observatory, München University, Scheinerstr. 1, 81679, Germany, and Center for Interdisciplinary Plasma Science (CIPS) e-mail: email@example.com
2 Toruń Centre for Astronomy, Nicholas Copernicus University, 87148 Piwnice/Toruń, Poland e-mail: firstname.lastname@example.org
Corresponding author: M. Hanasz, email@example.com
Accepted: 7 January 2003
We present a scenario for efficient magnetization of very young galaxies about 0.5 gigayears after the Big-Bang by a cosmic ray-driven dynamo. These objects experience a phase of strong star formation during this first 109 years. We transfer the knowledge of the connection between star formation and the production rate of cosmic rays by supernova remnants to such high redshift objects. Since the supernova rate is a direct measure for the production rate of cosmic rays we conclude that very young galaxies must be strong sources of cosmic rays. The key argument of our model is the finding that magnetic fields and cosmic rays are dynamically coupled, i.e. a strong cosmic ray source contains strong magnetic fields since the relativistic particles drive an efficient dynamo in a galaxy via their buoyancy. We construct a phenomenological model of a dynamo driven by buoyancy of cosmic rays and show that if azimuthal shearing is strong enough the dynamo amplification timescale is close to the buoyancy timescale of the order of several yr. We predict that young galaxies are strongly magnetized and may contribute significantly to the gamma-ray-background.
Key words: galaxies: evolution / ISM: magnetic fields / ISM: cosmic rays
© ESO, 2003