Physical conditions in the intergalactic medium

Abstract

Measurements of the spectrum of the cosmic microwave background radiation by COBE (Cosmic Background Explorer) limit the line integral of the electron pressure in intergalactic gas out to cosmological distances. The internal physical properties of diffuse bridges in the lobes of giant radio galaxies are also expected to reflect directly the pressure in this intergalactic medium that forms the environment of the radio structure. Surprisingly, the COBE limits rule out an intergalactic medium with the pressure indicated by the radio structures. This suggests that these regions are not thermally confined. However, an intergalactic medium composed of a mixture of hot nuclei and cold electrons which are not in thermal equilibrium is allowed by the COBE constraints, and processes during galaxy formation could provide a natural cause for an intergalactic medium with an energy density of the value indicated by the observed radio structures.