The Fanaroff-Riley transition and the optical luminosity of the host elliptical galaxy

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

Corresponding author: Gopal-Krishna, krishna@ncra.tifr.res.in

Received: 14 November 2000
Accepted: 9 April 2001

Abstract

We show that a model for radio source dynamics we had earlier proposed can readily reproduce the relationship between the radio power division separating the two Fanaroff-Riley classes of extragalactic radio sources and the optical luminosity of the host galaxy, as found by Owen & Ledlow ([CITE]). In our scenario, when less powerful jets eventually slow down to the point that the advance of the working surface (i.e., hotspot) becomes subsonic with respect to the external gas, the jet's collimation is severely weakened. This criterion distinguishes the powerful and well collimated FR II sources from the weaker sources producing the less collimated FR I type morphologies.