* Astronomy

Title: The disc-dominated host galaxy of FR-I radio source B2 0722+30
Authors: B. H. C. Emonts (1), C. N. Tadhunter (2), R. Morganti (3,4), T. A. Oosterloo (3,4), J. Holt (5), E. Brogt (6), G. van Moorsel (7) ((1) CSIRO-ATNF, (2) Univ. of Sheffield, (3) ASTRON, (4) Kapteyn Astron. Inst., (5) Leiden Obs., (6) Univ. of Arizona, (7) NRAO)

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 Ionisation 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.

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