PKS1932-46: a radio source in an interacting group?

We present the results of a multiwavelength study of the z= 0.23 radio source PKS1932−46. Integral field unit spectroscopy using the Visible Multi-object Spectrograph (VIMOS) on the Very Large Telescope (VLT) is used to study the morphology, kinematics and ionization state of the extended emission-line region (EELR) surrounding this source, and also a companion galaxy at a similar redshift. Near- and far-infrared imaging observations obtained using the New Technology Telescope and Spitzer are used to analyse the underlying galaxy morphologies and the nature of the active galactic nucleus (AGN).

The host galaxy is identified as an ∼M* elliptical. Combining Spitzer mid-infrared (mid-IR) with X-ray, optical and near-IR imaging observations of this source, we conclude that its AGN is underluminous for a radio source of this type, despite its status as a broad-line object. However, given its relatively large [O III] luminosity it is likely that the AGN was substantially more luminous in the recent past (≲104 yr ago).

The EELR is remarkably extensive and complex, reminiscent of the systems observed around sources at higher redshifts/radio powers, and the gas is predominantly ionized by a mixture of AGN photoionization and emission from young stars. We confirm the presence of a series of star-forming knots extending north–south from the host galaxy, with more prodigious star formation occurring in the merging companion galaxy to the north-east, which has sufficient luminosity at mid- to far-IR (MFIR) wavelengths to be classified as a luminous infrared galaxy (LIRG).

The most plausible explanation of our observations is that PKS1932−46 is a member of an interacting galaxy group, and that the impressive EELR is populated by star-forming, tidal debris. We suggest that the AGN itself may currently be fuelled by material associated either with the current interaction or with a previous merger event. Surprisingly, it is the companion object, rather than the radio source host galaxy, which is undergoing the bulk of the star formation activity within the group.