Hierarchical Structure in the Interstellar Medium as a Consequence of Self-Similar Dynamics

Details Hierarchical Structure in the Interstellar Medium as a Consequence of Self-Similar Dynamics Hierarchical Structure in the Interstellar Medium as a Consequence of Self-Similar Dynamics

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.4806v&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #48.06; Bulletin of the American Astronomical Society, Vol. 24, p.1199

Mathematics

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Scientific paper

The hydrodynamic equations governing the motions of the Interstellar Medium (ISM) are self-similar in the absence of specific forcing and dissipation mechanisms. It is thus argued that the rms relative density fluctuation L <(Delta rho rho) (2R > (1/2)) is independent of the average density of the medium in regions where the dynamics are dominated by inertial forces. Furthermore, in a highly supersonic turbulent medium like the ISM, the density can be considered to be passively advected by the flow, causing its distribution in time and space to be essentially a random variable. With these assumptions, it is shown, for the particular case of a normal distribution for Delta rho rho , that the probability of forming an overdense region is larger when its surroundings have already undergone a previous step of density enhancement than directly from the overall average value of the density. This naturally leads to a hierarchical nesting of the density fluctuations. The hypothesis that L <(Delta rho rho )(2bigr > (1/2)) is independent of is tested by performing a statistical analysis on the density field of a numerically simulated supersonic turbulent flow in two dimensions. Although obscured by the limited resolution, which limits the feasible density contrasts, the results tend to support the hypothesis.

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