Large scale magnetic fields in galaxies at high redshifts

¹ Institute for Astronomy, ETH Zurich, 8093 Zurich, Switzerland ;
e-mail: mbernet@phys.ethz.ch
² Los Alamos National Laboratory, PO Box 1663, Los Alamos NM 87545, USA
³ Observatoire de Genève, 51 Ch. Des Mailletes, 1290 Sauverny, Switzerland

Abstract

In a recent study we have used a large sample of extragalactic radio sources to investigate the redshift evolution of the Rotation Measure (RM) of polarized quasars up to z ≈ 3.0. We found that the dispersion in the RM distribution of quasars increases at higher redshifts and hypothesized that MgII intervening systems were responsible for the observed trend. To test this hypothesis, we have recently obtained high-resolution UVES/VLT spectra for 76 quasars in our sample and in the redshift range 0.6 < z < 2.0. We found a clear correlation between the presence of strong MgII systems and large RMs. This implies that normal galaxies at z ≈ 1 already had large-scale magnetic fields comparable to those seen today.