The disc-dominated host galaxy of FR-I radio source B2 0722+30
  We present new observational results that conclude that the nearby radio
galaxy B2 0722+30 is one of the very few known disc galaxies in the
low-redshift Universe that host a classical double-lobed radio source. In this
paper we use HI observations, deep optical imaging, stellar population
synthesis modelling and emission-line diagnostics to study the host galaxy,
classify the Active Galactic Nucleus and investigate environmental properties
under which a radio-loud AGN can occur in this system. Typical for spiral
galaxies, B2 0722+30 has a regularly rotating gaseous disc throughout which
star formation occurs. Dust heating by the ongoing star formation is likely
responsible for the high infrared luminosity of the system. The optical
emission-line properties of the central region identify a Low Ionization
Nuclear Emission-line Region (LINER)-type nucleus with a relatively low [OIII]
luminosity, in particular when compared with the total power of the Fanaroff &
Riley type-I radio source that is present in this system. This classifies B2
0722+30 as a classical radio galaxy rather than a typical Seyfert galaxy. The
environment of B2 0722+30 is extremely HI-rich, with several nearby interacting
galaxies. We argue that a gas-rich interaction involving B2 0722+30 is a likely
cause for the triggering of the radio-AGN and/or the fact that the radio source
managed to escape the optical boundaries of the host galaxy.
