High sensitivity H I observations of the nearby spiral galaxy NGC 2403 obtained with the VLA are presented and discussed. The properties of the extended, differentially rotating H I layer with its H I holes, spiral structure and outer warp are described. In addition, these new data reveal the presence of a faint, extended and kinematically anomalous component. This shows up in the H I line profiles as extended wings of emission towards the systemic velocity. In the central regions these wings are very broad (up to 150 km s −1 ) and indicate large deviations from circular motion. We have separated the anomalous gas component from the cold

We discuss new, high sensitivity H I observations of the spiral galaxy NGC 2403 which show extended emission at anomalous velocities with respect to the 'cold' disk. This 'anomalous' gas component (∼ 1/10 of the total H I mass) is probably located in the region of the halo and rotates more slowly (∼ 20−50 km s −1 ) than the gas in the disk. Moreover, it shows a distortion in the velocity field that we interpret as a large-scale radial motion (10−20 km s −1 inflow) towards the centre of the galaxy. The most likely explanation for its origin and kinematics seems to be that of a galactic fountain. There is, however, a significant part of the anomalous gas which seems to be moving contrary to rotation and is

A search for H i absorption has been made in 23 radio galaxies selected from a complete sample. The observations were made with the Australia Telescope Compact Array (ATCA), with the Very Large Array (VLA) and for one galaxy with the Westerbork Synthesis Radio Telescope (WSRT). In five galaxies H i absorption was detected. We investigate how the detection rate is distributed among galaxies with different radio and optical properties. Among the Fanaroff–Riley (FR) type I radio galaxies, only one object (10 per cent of the total) was detected in H i absorption. The H i absorption in these objects is likely to come from a nuclear disc, as found for other galaxies of this type (e.g. NGC 4261 and Hydra A). The low detection rate is consistent with the hypothesis (as suggested by optical and X‐ray data) that the ‘standard’ parsec‐scale, geometrically thick torus is not required in low‐luminosity radio galaxies. This is consistent with earlier optical work. In the case of FR type II powerful radio galaxies, no H i absorption has been detected in broad‐line radio galaxies, while three out of four narrow‐line radio galaxies have been detected (the one non‐detection having quite a high upper limit). All of these are compact or small radio galaxies. To first order this is consistent with the predictions of the unified schemes, assuming that the H i absorption is caused by an obscuring torus. However, the indications of this being the only cause of the absorption are not very strong. In particular, we find that in two of the three detected objects the H i is blueshifted compared with the systemic velocity. In the third galaxy (PKS 1549–79) two redshift systems (from the optical lines) are found. The uncertainty in the systemic velocity derived from optical lines is discussed. Finally, by also considering data available in the literature, we find a tendency for radio galaxies with a strong component of young stellar population and far‐infrared emission to show H i absorption. The overall richer interstellar medium that is likely to be present in these galaxies may be a factor in producing the absorption.

Abstract. We present high-spatial resolution 21-cm H I VLA observations of the radio galaxy 3C 305 (z = 0.041). These new high-resolution data show that the ∼1000 km s −1 broad H  absorption, earlier detected in low-resolution WSRT observations, is occurring against the bright, eastern radio lobe, about 1.6 kpc from the nucleus. We use new optical spectra taken with the WHT to make a detailed comparison of the kinematics of the neutral hydrogen with that of the ionised gas. The striking similarity between the complex kinematics of the two gas phases suggests that both the ionised gas and the neutral gas are part of the same outflow. Earlier studies of the ionised gas had already found evidence for a strong interaction between the radio jet and the interstellar medium at the location of the eastern radio lobe. Our results show that the fast outflow produced by this interaction also contains a component of neutral atomic hydrogen. The most likely interpretation is that the radio jet ionises the ISM and accelerates it to the high outflow velocities observed. Our observations demonstrate that, following this strong jet-cloud interaction, not all gas clouds are destroyed and that part of the gas can cool and become neutral. The mass outflow rate measured in 3C 305 is comparable, although at the lower end of the distribution, to that found in Ultra-Luminous IR galaxies. This suggests that AGN-driven outflows, and in particular jet-driven outflows, can have a similar impact on the evolution of a galaxy as starburst-driven superwinds.

We present WSRT, VLA and VLBI observations of the H i absorption in the radio galaxy NGC 315. The main result is that two H i absorbing systems are detected against the central region. In addition to the known highly redshifted, very narrow component, we detect relatively broad (FWZI ∼ 150 km s −1 ) absorption. This broad component is redshifted by ∼80 km s −1 compared to the systemic velocity, while the narrow absorption is redshifted ∼490 km s −1 . Both H i absorption components are spatially resolved at the pcscale of the VLBI observations. The broad component shows strong gradients in density (or excitation) and velocity along the jet. We conclude that this gas is physically close to the AGN, although the nature of the gas resulting in the broad absorption is not completely clear. The possibility that it is entrained by the radio jet (and partly responsible of the deceleration of the jet) appears unlikely. Gas located in a thick circumnuclear toroidal structure, with orientation similar to the dusty, circumnuclear disk observed with HST, cannot be completely ruled out although it appears difficult to reconcile with the observed morphology and kinematics of the H i. A perhaps more likely scenario is that the gas producing the broad absorption could be (directly or indirectly) connected with the fueling of the AGN, i.e. gas that is falling into the nucleus. If this is the case, the accretion rate derived is similar (considering all uncertainties) to that found for other X-ray luminous elliptical galaxies, although lower than that derived from the radio core luminosity for NGC 315. The data also show that, in contrast to the broad component, the density distribution of the narrow component is featureless. Moreover, in the WSRT observations we do detect a small amount of H i in emission a few kpc SW of the AGN, coincident with faint optical absorption features and at velocities very similar to the narrow absorption. This suggests that the gas causing the narrow absorption is not close to the AGN and is more likely caused by clouds falling into NGC 315. The environment of NGC 315 turns out to be indeed quite gas rich since we detect five gas-rich companion galaxies in the immediate vicinity of NGC 315.