Element segregation in giant galaxies and X-ray clusters

Abstract

We examine the process of element segregation by gravity in giant elliptical galaxies and X-ray clusters. We solve the full set of flow equations developed by Burgers for a multi-component fluid, under the assumption that magnetic fields slow the diffusion by a constant factor F_B. Compared to the previous calculations that neglected the residual heat flow terms, we find that diffusion is faster by ~20%. In clusters we find that the diffusion changes the local abundance typically by factors of 1+0.3(T/10^8 K)^1.5/F_B and 1+0.15(T/10^8 K)^1.5/F_B for helium and heavy elements, respectively, where T is the gas temperature. In elliptical galaxies, the corresponding factors are 1+0.2(T/10^7 K)^1.5/F_B and 1+0.1(T/10^7 K)^1.5/F_B, respectively. If the suppression factor F_B is modest, diffusion could significantly affect observational properties of hot X-ray clusters and cD galaxies. In particular, diffusion steepens the baryon distribution, increases the total X-ray luminosity, and changes the spectrum and evolution of stars that form out of the helium-rich gas. Detection of these diffusion signatures would allow to gauge the significance of the magnetic fields, which also inhibit thermal heat conduction as a mechanism for eliminating cooling flows in the same environments.