Simple analytical models for the cosmological evolution of the linear sizes of extragalactic radio sources have been developed based on ram and thermal pressures of the intergalactic medium. It was found that for suitable assumptions about the source magnetic field and energies, the evolution was of the form D approximately p(q)(1 + z)-n with n almost-equal-to 2.0 for ram pressure confinement and n almost-equal-to 3.0 for thermal pressure confinement. In all cases, the value of q was 0.33. It was suggested that quasars may be confined by ram pressure, while galaxies are subject to thermal confinement.
The Astrophysical Journal 11/1991; 383(1):56-59. DOI:10.1086/170762