Dressing a Naked Quasar: Star Formation and Active Galactic Nucleus Feedback in HE 0450−2958

Abstract

We present Australia Telescope Compact Array radio continuum observations of the quasar/galaxy system HE 0450-2958. An asymmetric triple linear morphology is observed, with the central radio component coincident with the quasar core and a second radio component associated with a companion galaxy at a projected distance of 7 kpc from the quasar. The system obeys the far-infrared to radio continuum correlation, implying that the radio emission is energetically dominated by star formation activity. However, there is undoubtedly some contribution to the overall radio emission from a low-luminosity active galactic nucleus (AGN) core and a pair of radio lobes. Long-baseline radio interferometric observations of the quasar core place a 3 ? upper limit of 0.6 mJy at 1400 MHz on the AGN contribution to the quasar's radio emission: less than 30% of the total. The remaining 70% of the radio emission from the quasar is associated with star formation activity and provides the first direct evidence of the quasar's host galaxy. A reanlaysis of the Very Large Telescope (VLT) spectroscopic data shows extended emission-line regions aligned with the radio axis and extended on scales of ~20 kpc. This is interpreted as evidence for jet-cloud interactions, similar to those observed in radio galaxies and Seyferts. The emission lines in the companion galaxy are consistent with radiative shocks, and its spatial association with the eastern radio lobe implies that large-scale jet-induced star formation has played a role in this galaxy's evolution.