Astron. Astrophys. 344, 7-16 (1999)

Radiative ages in a representative sample of low luminosity radio galaxies

P. Parma ¹, M. Murgia ^1,5, R. Morganti ¹, A. Capetti ², H.R. deRuiter ^1,3 and R. Fanti <sup>1,4

1</sup> Istituto di Radioastronomia, CNR, Via Gobetti 101, I-40129 Bologna, Italy
² Osservatorio Astronomico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese, Italy
³ Osservatorio Astronomico, Via Zamboni 33, I-40126 Bologna, Italy
⁴ Dipartimento di Fisica, Università di Bologna, Via Irnerio 46, I-40126 Bologna, Italy
⁵ Dipartimento di Astronomia, Università di Bologna, Via Zamboni 33, I-40126 Bologna, Italy

Received 12 June 1998 / Accepted 6 November 1998

Abstract

Two frequency observations, mainly at 1.4 and 5 GHz from the VLA, have been used to study spectral variations along the lobes of some nearby low luminosity radio galaxies that constitute a representative sample selected from the B2 catalogue. The variations of the spectral index have been interpreted as being due to synchrotron and inverse Compton losses and characteristic spectral ages are deduced for the relativistic electrons. The are in the range of several years. These correlate well with the source sizes. They also appear to be consistent with determined from ram-pressure arguments, if we make reasonable assumptions about the ambient gas density and allow for very moderate deviations from the equipartition conditions. There appears to be a significant difference between the radiative ages of sources in our sample and those of more powerful 3CR radio sources. We briefly discuss the possibility of re-acceleration processes and indicate some objects where these may occur.

Key words: radio continuum: galaxies galaxies: active

Send offprint requests to: P. Parma

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Contents

• 1. Introduction
• 2. Source selection and spectral data
• 3. Notes on individual sources
• 4. Determination of the radiative ages
  • 4.1. The models and the assumptions
  • 4.2. Spectral analysis
• 5. Discussion
  • 5.1. Two classes of source
  • 5.2. A comparison between spectral and dynamical ages
  • 5.3. Spectral ages and source sizes
  • 5.4. Is there particle re-acceleration?
  • 5.5. Spectral ages and radio power: a comparison with the 3CR radio galaxies
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: March 10, 1999
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