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The Relationship of the Fanaroff-Riley Classification of Extragalactic Radio Sources to Jet Physics

Published online by Cambridge University Press:  25 April 2016

G. V. Bicknell
G. V. Bicknell*
Affiliation:
Mount Stromlo and Siding Spring Observatories Australian National University
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Abstract

The Class I/Class II division of extragalactic radio sources by Fanaroff-Riley is a manifestation of important physical differences existing in radio sources.

It is proposed that the division essentially arises from the differing Mach numbers in Class I and Class II jets. The low Mach number, Class I jets are susceptible to turbulence, are decelerated by entrainment of the surrounding medium and maintain an anomalously high surface brightness as a result. The high Mach number, Class II jets are less turbulent and remain supersonic, produce high pressure shocks along their lengths and terminate via a strong shock against the IGM.

An analysis of the energy balance in both types of source reveals jet velocities of the order of 5-10,000 km s-1 for Class I jets and mildly relativistic velocities for Class II jets.

The important rôle of optical and X-ray observations in determining the gravitational field of pressure distribution in radio galaxies will be discussed with examples given of NGC1399 and IC4296.

Type
Contributions
Information
Publications of the Astronomical Society of Australia , Volume 6 , Issue 2 , 1985 , pp. 130 - 137
Copyright
Copyright © Astronomical Society of Australia 1985

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