Magnetic fields from reionisation

¹ Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK e-mail: mlanger@astro.ox.ac.uk
² Institut d'Astrophysique Spatiale, Université Paris-Sud, 91405 Orsay Cedex, France

Received: 5 May 2005
Accepted: 4 August 2005

Abstract

We present a complementary study to a new model for generating magnetic fields of cosmological interest. The driving mechanism is the photoionisation process by photons provided by the first luminous sources. Investigating the transient regime at the onset of inhomogeneous reionisation, we show that magnetic field amplitudes as high as Gauss can be obtained within a source lifetime. Photons with energies above the ionisation threshold accelerate electrons, inducing magnetic fields outside the Strömgren spheres which surround the ionising sources. Thanks to their mean free path, photons with higher energies propagate further and lead to magnetic field generation deeper in the neutral medium. We find that soft X-ray photons could contribute to a significant premagnetisation of the intergalactic medium at a redshift of .