Diffusion of Elements in the Interstellar Medium in Early-Type Galaxies
  We consider the role of diffusion in the redistribution of elements in the
hot interstellar medium (ISM) of early-type galaxies. It is well known that
gravitational sedimentation can affect significantly the abundances of helium
and heavy elements in the intracluster gas of massive galaxy clusters. The
self-similarity of the temperature profiles and tight mass--temperature
relation of relaxed cool-core clusters suggest that the maximum effect of
sedimentation take place in the most massive virialized objects in the
Universe. However, Chandra and XMM-Newton observations demonstrate more complex
scaling relations between the masses of early-type galaxies and other
parameters, such as the ISM temperature and gas mass fraction. An important
fact is that early-type galaxies can show both decreasing and increasing radial
temperature profiles. We have calculated the diffusion based on the observed
gas density and temperature distributions for 13 early-type galaxies that
belonging to the different environments and cover a wide range of X-ray
luminosities. To estimate the maximum effect of sedimentation and thermal
diffusion, we have solved the full set of Burgers' equations for a
non-magnetized ISM plasma. The results obtained demonstrate a considerable
increase of the He/H ratio within one effective radius for all galaxies of our
sample. For galaxies with a flat or declining radial temperature profile the
average increase of the helium abundance is 60\% in one billion years of
diffusion. The revealed effect can introduce a significant bias in the metal
abundance measurements based on X-ray spectroscopy and can affect the evolution
of stars that could be formed from a gas with a high helium abundance.
