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The lives of FR I radio galaxies

P. Parma·M. Murgia·H. R. de Ruiter·R. Fanti
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Abstract

After a brief introduction to the morphological properties of FRI radio sources, we discuss the possibility that FRI jets are relativistic at their bases and decelerate quickly to non-relativistic velocities. From two-frequency data we determine spectral index distributions and consequently the ages of FRI sources. We show that in the large majority of cases synchrotron theory provides unambiguous and plausible answers; in a few objects re-acceleration of electrons may be needed. The derived ages are of the order 10^7-10^8 years, 2-4 times larger than the ages inferred from dynamical arguments and a factor 5-10 larger than the ages of FRII sources. The linear sizes of FRI and FRII sources make it unlikely that many FRII's evolve into FRI's. A brief discussion is given of the possibility that radio sources go through different cycles of activity.

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P. Parma, M. Murgia, H. R. de Ruiter, R. Fanti. 1999-10-14. The lives of FR I radio galaxies. https://doi.org/10.1016/s1387-6473(01)00201-9

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