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We present neutral hydrogen (H I) and warm molecular hydrogen (H2) observations of the young (102 yr) radio galaxy PKS B1718-649. We study the morphology and the kinematics of both gas components, focusing, in particular, on their properties in relation to the triggering of the radio activity. The regular kinematics of the large scale H I disk, seen in emission, suggests that an interaction event occurred too long ago to be responsible for the recent triggering of the radio activity. In absorption, we detect two absorption lines along the narrow line of sight of the compact ({r yr) radio galaxy PKS B1718-649. We study the morphology and the kinematics of both gas components, focusing, in particular, on their properties in relation to the triggering of the radio activity. The regular kinematics of the large scale H I disk, seen in emission, suggests that an interaction event occurred too long ago to be responsible for the recent triggering of the radio activity. In absorption, we detect two absorption lines along the narrow line of sight of the compact ({r 2 1-0 S(1) ro-vibrational line) in the innermost kilo-parsec of the galaxy appears to be distributed in a circum-nuclear disk following the regular kinematics of the H I and of the stellar component. An exception to this behaviour arises only in the very centre, where a highly dispersed component is detected. These particular H I and H2 features suggest that a strong interplay between the radio source and the surrounding ISM is ongoing. The physical properties of the cold gas in the proximity of the radio source may regulate the accretion recently triggered in this AGN.

An important aspect of solving the long-standing question as to what triggers various types of active galactic nuclei (AGN) involves a thorough understanding of the overall properties and formation history of their host galaxies. This is the second in a series of papers that systematically study the large-scale properties of cold neutral hydrogen (H 0 gas in nearby radio galaxies. The main goal is to investigate the importance of gas-rich galaxy mergers and interactions among radio-loud AGN. In this paper, we present results of a complete sample of classical low-power radio galaxies. We find that extended Fanaroff & Riley type-I radio sources are generally not associated with gas-rich galaxy mergers or ongoing violent interactions, but occur in early-type galaxies without large (greater than or similar to 10(8) M(circle dot)) amounts of extended neutral hydrogen gas. In contrast, enormous discs/rings of H I gas (with sizes up to 190 kpc and masses up to 2 x 10(10) M(circle dot)) are detected around the host galaxies of a significant fraction of the compact radio sources in our sample. This segregation in H I mass with radio-source size likely indicates that either these compact radio sources are confined by large amounts of gas in the central region or that their fuelling is inefficient and different from the fuelling process of classical FR I radio sources. To first order, the overall Hi properties of our complete sample (detection rate, mass and morphology) appear similar to those of radio-quiet early-type galaxies. If confirmed by better statistics, this would imply that low-power radio-AGN activity may be a short and recurrent phase that occurs at some point during the lifetime of many early-type galaxies.

A number of O stars are suspected to have (weak) magnetic fields because of the observed cyclical variability in their UV wind-lines. However, direct detections of these magnetic fields with optical spectropolarimetry have proven to be very difficult. We have searched for non-thermal radio emission, which would be a strong indication for the presence of a magnetic field. Of our 5 selected candidate magnetic O stars, 3 are detected: xi Per, which we find to have a non-thermal spectrum, and lambda Cep and alpha Cam which show a thermal spectrum. We also find that the fluxes are lower than the expected free-free (thermal) contribution of the stellar wind. This is in agreement with recent findings that the mass-loss rates from O stars using Halpha are overestimated because of clumping in the inner part of the stellar wind.