COSMOLOGY WITH POWERFUL EXTENDED RADIO-SOURCES

Distant powerful radio sources would provide a useful cosmological too l if an intrinsic length or luminosity could be estimated from the obs ervations in a way that is independent of the coordinate distance to t he source. A model for the propagation of the radio lobes of powerful extended radio sources is presented here; the model is written in term s of fundamental physical variables such as the luminosity in directed kinetic energy and the ambient gas density, rather than observables s uch as the radio power. It is shown that the fundamental physical vari ables may be estimated from observed quantities. The model parameter b eta that relates the characteristic time the central engine is produci ng a collimated outflow to the luminosity in directed kinetic energy i s constrained by low-redshift observations and extrapolated to high re dshift. The application of the model to powerful extended radio source s allows an estimate of the characteristic source sizes that is nearly independent of the coordinate distance to the source, and thus is bas ically independent of the de/acceleration parameter q0. The characteri stic source sizes estimated in the context of the model may be compare d with the observed median source sizes, where each source size is det ermined directly from the angular extent of the source, the source red shift, and the coordinate distance to the source. The comparison of th e intrinsic source sizes estimated using the model, which are nearly i ndependent of q0, with the median source sizes estimated using the ang ular sizes of the sources, which depend on q0, constrains the allowed range of q0. The basic model and method is presented and discussed and is applied to one published data set consisting of 10 radio galaxies. Taken at face value, the data favor a low value of q0; a low value of q0 implies that either space curvature or a cosmological constant is important at the present epoch. Note that Doppler boosting and beaming of radio emission are unlikely to be important in these systems since the relevant flow velocities are small compared with the speed of lig ht. This analysis has broad implications for the environments of power ful extended radio sources and for models for extracting the luminosit y in directed kinetic energy from the central compact object.