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Astron. Astrophys. 363, 507-516 (2000)

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Extragalactic radio sources with hybrid morphology: implications for the Fanaroff-Riley dichotomy

Gopal-Krishna 1 and P.J. Wiita 2,3

1 Tata Institute of Fundamental Research, National Centre for Radio Astrophysics, Pune University Campus, Post Bag No. 3, Ganeshkhind, Pune 411 007, India (krishna@ncra.tifr.res.in)
2 Princeton University, Department of Astrophysical Sciences, Princeton, NJ 08544-1001, USA (wiita@astro.princeton.edu),
3 on leave from the Department of Physics & Astronomy, Georgia State University, University Plaza, Atlanta, GA 30303-3083, USA (wiita@chara.gsu.edu)

Received 2 August 2000 / Accepted 15 September 2000


We provide observational and theoretical perspectives on the currently much debated issue of the Fanaroff-Riley (FR) morphological dichotomy of extragalactic radio sources. In this context we introduce a new, albeit rare, class of double radio sources in which the two lobes exhibit clearly different FR morphologies. It is argued that such `HYbrid MOrphology Radio Sources', or HYMORS, could be used to effectively constrain the theoretical mechanisms proposed for the FR dichotomy. Basically, the existence of HYMORS supports explanations for the FR dichotomy based upon jet interaction with the medium external to the central engine, and appears quite difficult to reconcile with the class of explanations that posit fundamental differences in the central engine, such as black hole spin or jet composition, to be responsible for the two FR classes of double radio sources.

Key words: black hole physics – galaxies: active – galaxies: elliptical and lenticular, cD – galaxies: jets – galaxies: nuclei – radio continuum: galaxies

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© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000