W. H. Kegel

Heating of the intracluster medium

The gravitational interaction of the system of galaxies and the ICM are treated by fluctuation theory. Fluctuation theory seems to be more adequate to describe the gravitational interaction than local theories used up to now, because gravitation is a long-range force. Therefore, the dynamical friction and energy transfer depends mainly on the global structure of the gravitational wakes induced by the galaxies in the ICM. The ICM is described hydrodynamically by a nonpolytropic gas. The heating rate is derived as a local quantity on scales characteristic for cluster properties in quasi-linear approximation. The parameter dependence is given explicitly. The Coma cluster is taken as an example to show that mechanical heating by fluctuations may be essential for the structure of the cluster halos and cooling flows. 19 refs.

Velocity Correlations in Turbulent Molecular Clouds

The observed widths of molecular lines indicate that molecular clouds are in a highly turbulent state with supersonic internal velocities. At the same time molecular clouds are highly fragmented into substructures exhibiting large density contrasts. These substructures seem to be arranged in a hierarchical order scheme where one can think of newly formed stars representing the smallest spatial scale of ordering. Stars, protostars and even dense clumps can be regarded as being hydrodynamically decoupled from the ambient gas. Thus, in an idealized way, one can think of molecular clouds as being a gravitationally coupled system consisting of gas (continuous component) and’ point-masses’ (particle component) randomly moving through the gas. The random motion of these’ point-masses’ is accompanied by spatial and temporal fluctuations of their gravitational potential which, in turn, induce velocity and density fluctuations of the gas [1],[2],[4],[5]