Fields and filaments in the core of the Centaurus cluster

We present high-resolution images of the Faraday rotation measure (RM) structure of the radio galaxy PKS 1246-410 at the centre of the Centaurus cluster. Comparison with H alpha-line and soft X-ray emission reveals a correspondence between the line-emitting gas, the soft X-ray emitting gas, regions with an excess in the RM images and signs of depolarization. Magnetic field strengths of 25 mu G, organized on scales of similar to 1 kpc and intermixed with gas at a temperature of 5 x 106 K with a density of similar to 0.1 cm(-3), can reproduce the observed RM excess, the depolarization and the observed X-ray surface brightness. This hot gas may be in pressure equilibrium with the optical line-emitting gas, but the magnetic field strength of 25 mu G associated with the hot gas provides only 10 per cent of the thermal pressure and is therefore insufficient to account for the stability of the line-emitting filaments.