VLA H I Zeeman observations of Centaurus A

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.