POWERFUL EXTENDED RADIO-SOURCES AS TOOLS TO ESTIMATE AMBIENT GAS DENSITIES, JET LUMINOSITIES, AND OTHER KEY PHYSICAL PARAMETERS

It would be quite valuable if the radio properties of powerful, extend ed radio sources could be used to deduce key physical quantities such as the density of the ambient gas in the vicinity of a radio source. I t is shown here that radio observations can be used to estimate the am bient gas density, the luminosity in directed kinetic energy, and othe r key physical parameters relevant to the radio source and its gaseous environment. The methods described are applied to radio galaxies and radio-loud quasars with redshifts from about 0 to 2. The ambient gas d ensity in the vicinity of the radio lobes is estimated by applying the strong shock jump conditions across the forward edge of the radio bri dge (referred to as the radio lobe); this requires that the lobe press ure and the lobe propagation velocity be known. The lobe pressure is e stimated assuming minimum energy conditions, and the local propagation velocity is estimated from the effects of synchrotron and inverse Com pton aging of relativistic electrons on the radio spectrum across the radio bridge. At present this appears to be the only method of estimat ing the ambient gas density (as a single parameter) in the vicinity of distant powerful radio sources, and this first application of the met hod indicates that it provides a good rough estimate of the ambient ga s density. One interesting result is that galaxies and quasars are fou nd to lie in similar gaseous environments. Another is that the composi te density profile is similar to that of gas in clusters of galaxies a nd is normalized to Cygnus A, which is known to be in a cluster with a hot intracluster medium in place. This suggests that the powerful rad io sources considered here are surrounded by extended gaseous halos li ke those in present-day galaxy clusters, with the radio source interio r to the core of the gaseous halo. One interpretation is that the radi o sources considered are in the cores of clusters of galaxies with the ir intracluster media in place, which would suggest that some clusters , or at least cluster cores, exist out to redshifts of about 2. The lo be propagation velocity, the rate at which energy is channeled from th e central engine in the form of a collimated outflow (known as the lum inosity in directed kinetic energy), and a time-independent characteri stic source size, which provides a calibrated yardstick and hence is a useful cosmological tool, are also discussed. The basic assumptions a dopted by Daly (1994) in the use of these sources as cosmological prob es are empirically tested; it is found that the data are consistent wi th the assumptions adopted. Relations between different parameters are investigated and discussed in detail. This leads to a wide perspectiv e and good understanding of the environments and nuclear properties of powerful extended radio sources. For example, a maximum value for the energy extraction rate is seen in the present data set and may imply an upper limit to this quantity. And the lobe propagation velocity may also have a maximum value, indicating that there may be an upper limi t to the Mach number at which the radio lobe propagates into the ambie nt medium. The limited data set used here supports the idea that radio galaxies and radio-loud quasars are intrinsically similar but appear different due to different viewing angles, however, they may not be in trinsically identical. Perhaps the two types of active galactic nucleu s (AGN) activity observed, highly collimated outflows and radiant ener gy from the nuclear region of the AGN, should be identified with the t wo ultimate energy sources associated with massive compact objects: th e spin energy of the massive compact object and the gravitational ener gy of matter falling onto the object, respectively. Then, the three ty pes of AGN observed may not be intrinsically identical: radio-quiet qu asars result when only the gravitational energy is being tapped, radio -loud quasars result when both energy sources are being tapped, and ra dio galaxies result when the spin energy of the massive compact object is being tapped. Since the sources are likely to be anisotropic, such a scheme is likely to be working in parallel with orientation unified models.