EDP Sciences
Free access
Volume 401, Number 3, April III 2003
Page(s) 809 - 816
Section Cosmology
DOI http://dx.doi.org/10.1051/0004-6361:20030212

A&A 401, 809-816 (2003)
DOI: 10.1051/0004-6361:20030212

Strong magnetic fields and cosmic rays in very young galaxies

H. Lesch1 and M. Hanasz2

1  University Observatory, München University, Scheinerstr. 1, 81679, Germany, and Center for Interdisciplinary Plasma Science (CIPS)
    e-mail: lesch@usm.uni-muenchen.de
2  Torun Centre for Astronomy, Nicholas Copernicus University, 87148 Piwnice/Torun, Poland
    e-mail: mhanasz@astri.uni.torun.pl

(Received 24 September 2002 / 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 $10^7 \div 10^8$ 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

Offprint request: M. Hanasz, mhanasz@astri.uni.torun.pl

© ESO 2003