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Astron. Astrophys. 329, 431-442 (1998)


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Spectral indices, particle ages, and the ambient medium
of giant radio galaxies

K.-H. Mack 1, 2, U. Klein 1, C.P. O'Dea 3, A.G. Willis 4 and L. Saripalli 1, 5

1 Radioastronomisches Institut, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
2 Istituto di Radioastronomia del CNR, Via P. Gobetti 101, I-40129 Bologna, Italy
3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
4 Dominion Radio Astrophysical Observatory, P. O. Box 248, Penticton, BC, V2A 6K3, Canada
5 Raman Research Institute, Sadashiva Nagar, Bangalore 560 080, India

Received 27 January 1997 / Accepted 20 August 1997

Abstract

We present a spectral aging study of a sample of 5 giant radio galaxies based on radio continuum data obtained at frequencies between 326 MHz and 10.6 GHz. Using synchrotron loss models, we determined injection spectral indices and particle ages where possible. The results suggest ages not older than 4 [FORMULA] yr, a value that is typical for radio galaxies with "normal" sizes. From equilibrium considerations between lobes and jets on the one hand and the ambient medium on the other we derived estimates of the density of the intergalactic medium, with average values in the range of a few [FORMULA] cm-3.

Key words: radio continuum: galaxies – galaxies: individual: NGC 315; DA 240; 3C 236; 3C 326; NGC 6251

Send offprint requests to: K.-H. Mack, Bologna address

© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997
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