AGN SURVEYS ASP Conference Series, Vol. 284, 2002 R.F. Green, E. Ye. Khachikian, D.B. Sanders Energy Density and Radiation Losses in Giant Radio Galaxies Marek Jamrozy & Jerzy Machalski Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30-244 Krakow, Poland Abstract. The volumes, equipartition energy density, and radiation losses due to the synchrotron and inverse Compton interactions as a function of redshift and projected linear size of Giant radio galaxies are discussed. The new results are based on data from three samples: 1) Ishwara-Chandra & Saikia (1999), 2) Schoenmakers (Ph.D. Thesis, 1999), and 3) Machalski, Jamrozy & Zola (2001). 1. Introduction Giant radio sources with linear sizes greater than 1 Mpc form an extreme class of extragalactic radio sources. The majority of them are radio galaxies at z < 0.3 ~ 0.4. They are of special interest for studying a number of as- trophysical problems. One of them is under what circumstances some sources evolve to "giant" sizes. These Giants must be extremely old and/or located in a very underdense environment, and/or have a stronger central source of energy as compared to smaller radio sources. It is very important to compare various physical parameters of normal-size and giant sources. Here we present a contri- bution to the following problems: 1) how does the energy density in the lobes of FRII-type radio sources evolve with redshift, and how does it relate to the evolution of energy and pressure of the intergalactic medium (IGM), and 2) how do radiative losses differentiate the lobes of giant sources from normal ones. 2. Results Correlation between the Energy Density and Redshift Using the Spearman partial rank correlation coefficients between the equiparti- tion energy density in lobes u me and redshift and/or power P\ .4 for 49 Giants with D > 1 Mpc, we deduced that the apparent correlation u me — z arises from two others: u me — P and P — z. We also checked the correlation be- tween u me and size D. The relevant partial correlations for 32 Giants with 10 24.2 < P j ^ W H z ^ s r -1 ] < 10 250 show that there is a significant correlation u me — D which implies the same between the energy density and volume. There- fore, there is no evidence that the undetected dependence between the energy density and redshift does not exist; it can be much weaker than the detected Ume — P and Ume — D correlations. The apparent distribution of the energy density vs. redshift is shown in Fig. 1, left panel. Correlation between the Pressure Ratio and the Lobe Size A non-relativistic, diffuse and uniform IGM in thermal equilibrium has an elec- tron pressure, PIGMJ which should increase with redshift as PIGM(Z) = Po(l + z) 5 295 terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100030876 Downloaded from https://www.cambridge.org/core. IP address: 54.161.69.107, on 08 Jun 2020 at 01:02:54, subject to the Cambridge Core