2010A&A...523A...9H

Unification models for active galactic nuclei, AGN, predict that all quasars (radio sources associated with quasi-stellar objects) should be at a substantial angle with the sky plane. We test the predictions of the orientation unification model with the morphological and polarization properties of a giant quasar. The giant double-lobed radio source 4C34.47, which is associated with quasi-stellar object B1721+343, is mapped at arcsecond scale resolution, and the data are subsequently analyzed within the context of current models for extragalactic radio sources. Quasar 4C34.47 displays a straight one-sided jet, measuring a record length of 380kpc in its double-lobed radio structure. Assuming an intrinsically symmetric two-sided jet structure the radio source jet axis must be at least 33° away from the sky plane, that is within 57° from the line of sight. The radio polarization properties indicate that this giant source has largely outgrown the depolarizing halo that is generally associated with the host galaxies of powerful radio sources. The measured small depolarization asymmetry nevertheless agrees with its inferred orientation. All data for this giant radio source agree with its preferred orientation as predicted within the unification scheme for powerful radio sources. Seen under a small aspect angle the radio source is large, but not excessively large. The global properties of 4C34.47 do not differ from other giant (old) FR2 radio sources: it is a slowly expanding low-luminosity radio source.