A radio study of the Seyfert galaxy IC 5063: Evidence for fast gas outflow

We present new radio continuum (8 and 1.4 GHz) and H I 21 cm line observations of the Seyfert 2 galaxy IC 5063 (PKS 2048-572), obtained with the Australia Telescope Compact Array. The high-resolution 8 GHz image reveals a linear triple structure similar to 4" (1.3 kpc) in size. This small-scale radio emission shows a strong morphological association with the narrow-line region (NLR), the inner part of the optical emission-line region. It is aligned with the inner dust lane and is oriented perpendicularly to the position angle of the optical polarization. We identify the radio nucleus as the central blob of the radio emission. At 21 cm, very broad (similar to 700 km s(-1)) H I absorption is observed against the strong continuum source. This absorption is almost entirely blueshifted, indicating a fast net outflow, but a faint and narrow redshifted component is also present. In IC 5063 we see clear evidence, both morphological and kinematic, of strong shocks resulting from the interaction between the radio plasma and the interstellar medium (ISM) in the central few kiloparsecs. However, we estimate the energy flux in the radio plasma to be an order of magnitude smaller than the energy flux emitted in emission lines. Thus, although strong shocks associated with the jet/ISM interaction occur, and could contribute locally to the ionization of the NLR, they are unlikely to account solely for the global ionization of the emission-line region, particularly at large distances. The main structure of the H I emission is a warped disk associated with the system of dust lanes of R similar to 2' (similar to 38 kpc, corresponding to similar to 5 effective radii). The lack of kinematically disturbed gas (both neutral and ionized) outside the central few kiloparsecs, the warped structure of the large-scale disk, and the close morphological connection between the inner dust lanes and the large-scale ionized gas all support the idea that the gas at large radii is photoionized by the central region, while shadowing effects are important in defining its X-shaped morphology. From the kinematics of the ionized and neutral gas, we find evidence for a dark halo in IC 5063, with properties very similar to those observed in some other early-type galaxies.