Merger-origin of radio galaxies investigated with H I observations
  We present results of an HI study of a complete sample of nearby radio galaxies. Our goal is to investigate whether merger or interaction events could be at the origin of the radio-AGN activity. Around five of our radio galaxies, hosted mainly by early-type galaxies, we detect extended HI in emission. In most cases this HI is distributed in large (up to 190 kpc) and massive (up to M(HI) ~ 10^10 M(sun)) disk- or ring-like structures, that show fairly regular rotation around the host galaxy. This suggests that in these systems a major merger did occur, but at least several Gyr ago. For the HI-rich radio galaxy B2 0648+27 we confirm such a merger origin through the detection of a post-starburst stellar population that dominates the visible light throughout this system. The timescale of the current episode of radio-AGN activity in our HI-rich radio galaxies is many orders of magnitude smaller than the merger timescales. Therefore the radio-AGN activity either started late in the lifetime of the merger event, or is not directly related to the merger event at all. Another intriguing result is that the HI-rich (> 10^9 M(sun)) radio galaxies in our sample all have compact radio sources, while none of the extended radio sources contain these amounts of extended HI. This strongly suggests that there is a relation between the size of the radio jet and the presence of large amounts of neutral gas associated with the host galaxy. 
B. H. C. Emonts (1), R. Morganti (1,2), T. A. Oosterloo (1,2), J. M.   van der Hulst (1), C. N. Tadhunter (3), G. van Moorse...