Evolution of radio jets in galactic halos and the intergalactic medium

  • Paul J. Wiita
  • Gopal-Krishna
VI. Radio Observations and Modeling
Part of the Lecture Notes in Physics book series (LNP, volume 307)


Analytical models for the propagation of relativistic jets through both a hot interstellar medium and an even hotter intergalactic medium (IGM) are considered and shown to have surprisingly good predictive powers. We use the best observational data for the current properties of these media and make reasonable estimates of their cosmological evolutions. Limiting cases for the behavior of jets crossing the interface between them are analyzed and can quantitatively explain:

  1. 1)

    the current mean linear-size of double radio sources (∼350 kpc);

  2. 2)

    the decrease in linear-size with cosmological redshift, z; and,

  3. 3)

    the increase in linear-size with radio power (at fixed z).


Because both very extended jets and very weak ones can allow the energy density in the lobes to become comparable to that of the microwave background, inverse Compton losses of the synchrotron emitting electrons against the background photons must also be considered. We can then argue that the most intrinsically powerful radio sources produce giant radio galaxies (those whose linear size exceeds 1.5 Mpc) and can also explain:

  1. 4)

    the number of observed giant sources at z ≲ 0.2 (about 20 known);

  2. 5)

    the median observed radio power of such sources (∼1026W/Hz at 408 MHz); and,

  3. 6)

    the relative prominence of their nuclei in the radio band. We predict the existence of a significant number of giant radio galaxies in the redshift range 0.2 ≲ z ≲ 0.6.


Finally, we argue that the break in the local radio luminosity function (LRLF) of isolated elliptical radio sources at about 1024 W/Hz at 1 GHz is mostly due to the fact that very weak jets are likely to become subsonic even within the halo. When this effect, which leads to such beams quickly fading away as radio sources, and the inverse Compton losses are convolved with an assumed universal power-law LRLF, the observed flattening at low radio powers is obtained.


Radio Source Radio Galaxy Radio Luminosity Giant Radio Galaxy Inverse Compton Loss 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • Paul J. Wiita
    • 1
  • Gopal-Krishna
    • 2
  1. 1.Department of Physics and AstronomyGeorgia State University AtlantaGeorgia
  2. 2.Radio Astronomy Group, Tata Institute of Fundamental ResearchIndian Institute of Science CampusBangaloreIndia

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