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Session 94 - Large-Scale Structure: Observations and Theory.
Oral session, Wednesday, January 17
Corte Real, Hilton

[94.06] Hierarchical clustering and a detailed description of the merger history tree

R. K. Sheth (U.C. Berkeley)

The Press--Schechter description of gravitational clustering from an initially Poisson distribution is equivalent to the well studied Galton--Watson branching process. This correspondence is used to provide a detailed description of the evolution of hierarchical clustering, including a complete description of the merger history tree. An analytic expression for the merger history of any given Poisson Press--Schechter clump is obtained. This expression allows one to calculate the partition function of merger history trees. The distribution function of counts in randomly placed cells, as a function of time, is also obtained. Thus, the Press--Schechter description of the gravitational evolution of clustering from an initially Poisson distribution is now complete. The detailed predictions of the model are in good agreement with N-body simulations. One way to extend these results to more general Gaussian initial conditions is discussed. The counts in cells distribution derived here is in good agreement with the observed distribution of galaxies. One example of the usefulness of knowing the merger history tree is that it allows one to explain and quantify observations at relatively high redshift such as the Butcher--Oemler effect.

Program listing for Wednesday