Element segregation in giant galaxies and X‐ray clusters

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 multicomponent fluid, under the assumption that magnetic fields slow the diffusion by a constant factor F B . Compared with the previous calculations that neglected the residual heat flow terms, we find that diffusion is faster by ∼20 per cent. 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 us 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.