view Abstract Citations (37) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Temperature of Intergalactic Matter Gould, Robert J. ; Ramsay, William Abstract This paper considers the various processes which determine the temperature of intergalactic matter. Heating by cosmic-ray ionization and dissipation of hydrodynamic turbulence are estimated, as well as cooling by inelastic electron collisions with H, He,, and He+, and by bremsstrahlung and recombination radiation. The effects of the presence of a `cosmic' abundance of helium in intergalactic space are significant because of the associated strong cooling for temperatures of 3 X 10 " to 2 X 10 " K. The effects of dielectronic recombination are included for helium. It is shown that heating by a universal cosmic-ray flux can maintain temperatures of 1-S X 10 " K against cooling by electron collisions with H, He, and He+ for a cosmic He/H abundance and local hydrogen densities of 10- 10- particles/cm3. However, the relaxation time for hydrogen and singly ionized helium recombination is about ten times the cosmic expansion time of TE = 1017 sec for hydrogen densities of 10- at these temperatures, while doubly ionized helium recombines in about 3 X 1017 sec. Thus, unless intergalactic matter exists in "clouds" in which the hydrogen density is ten times the usually assumed mean of 10- ionization steady-state conditions may not exist. Moreover, if the temperature of the intergalactic gas was initially greater than about 2 X 10 " K, the cooling processes are not sufficient to cause an appreciable lowering of temperature in a time TE, 50 that such an initially hot intergalactic gas could remain hot. Dissipation of turbulent energy in a time «TE could produce an initially hot gas. Galaxy formation is considered briefly. It is suggested that an intergalactic gas at about 2 X 10 " K is unstable to density condensations, due to the strong cooling by He+ at lower temperatures; such thermal instabilities could result in the formation of galaxies and galaxy clusters. Publication: The Astrophysical Journal Pub Date: May 1966 DOI: 10.1086/148639 Bibcode: 1966ApJ...144..587G full text sources ADS |