PARSEC-SCALE MORPHOLOGY OF PKS-2152-699 AND THE RADIO OPTICAL MISALIGNMENT

We present the first very-long-baseline interferometry (VLBI) image of the parsec-scale structure in the nearby (z=0.0282) Fanaroff-Riley ty pe II radio galaxy PKS 2152-699, revealing the core-jet morphology typ ical of compact radio sources. Tadhunter ct al. [MNRAS, 235, 403 (1988 )] have identified this object as one in which the radio axis and opti cal emission line features on the kiloparsec-scale appear to have an o bvious connection but are somewhat misaligned, They interpret this rel ationship as most likely being due to an interaction between the radio jet and an extra-nuclear cloud of gas, the misalignment possibly caus ed by the deflection of the radio jet in the interaction. The VLBI obs ervations presented here further strengthen the evidence for the inter action interpretation. The parsec-scale radio jet aligns strongly with optical emission line features, and not with the kiloparsec-scale rad io structure. We explore a mechanism which could produce the misalignm ent and which is consistent with the interaction concept, namely obliq ue shocks in a relativistic jet. With a minimal model we find that rea sonable values of the model parameters can provide the required misali gnment over a wide range of initial conditions. (C) 1996 American Astr onomical Society.