2002ApJ...564..696S

We present H I absorption observations toward the nucleus and neighboring radio features of Centaurus A, with the aim of studying the magnetic field using the Zeeman effect. The H I profiles toward the nucleus reveal for the first time a broad absorption component that extends up to 635 km.s^–1 and is centered near 583 km.s^–1. This broad component may be a blend of absorption in several clouds located in the ∼100 pc radius circumnuclear ring of Cen A. We set upper limits on the line-of-sight magnetic field (B_los) in Cen A in the regions traced by the H I absorption components. The best value (fit±1 σ error) for B_los in the dust lane is -3±7 µG. For the redshifted narrow line width components observed toward the nucleus, B_los is ∼10±20 µG. If we assume the spin temperature T_s≤50 K in these redshifted clouds, our analysis shows that the magnetic fields will be energetically significant if B_los≥5 µG for cloud sizes around a few parsecs or larger.