Stripped tails of early-type galaxies infalling into clusters: gas dynamics and the viscosity of the intracluster medium
Ralph Kraft
Smithsonian Astrophysical Observatory

One of the most important outstanding problems in astrophysics is determining the magnitude of the transport coefficients, that is the viscosity and thermal conduction, of all phases of galactic and extragalactic plasma. This problem is particularly acute in the study of the intracluster medium (ICM) of cluster of galaxies, and the presence or absence of viscosity plays an important role in the thermodynamic evolution of the gas and the relative importance of sources and sinks of energy. In a terrestrial setting, the viscosity of a fluid can be directly measured by studying the wake of flow behind a solid obstruction. In an astrophysical context, the closest analogy is the infall of an early-type galaxy into a cluster of galaxies. As the galaxy falls into the potential, the outer layers of gas are stripped off and form a long tail. If the ICM viscosity is low (i.e. the Reynolds number is high), Kelvin-Helmholtz instabilities (KHIs) will efficiently mix the ICM gas with the galaxy gas. If the ICM viscosity is low, KHIs will be suppressed, the galaxy gas will not mix with the ICM, and a long, cold tail will will formed. The presence or absence of this cold then is, in principle, a direct measurement of the viscosity of the ICM. In this talk I will present results from a combined analysis of deep Chandra observations of the stripped tails of nearby early-type galaxies with specially tailored hydrodynamic simulations to characterize the flow patterns and efficiency of mixing to measure the viscosity of the ICM.

Date:	Jeudi, 18 septembre 2014
Time:	11:30
Where:	Université de Montréal
	Pavillon Roger-Gaudry, local D-460
Contact:	Julie Hlavacek-Larrondo