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Astron. Astrophys. 321, 691-695 (1997)

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Substructure effects on the collapse of density perturbations

A.  Del Popolo and M. Gambera

Istituto di Astronomia dell'Università di Catania, Città Universitaria, Viale A. Doria 6, I-95125 Catania, Italy

Received 30 October 1996 / Accepted 6 September 1996


We solve numerically the equations of motion for the collapse of a shell of baryonic matter, made of galaxies and substructure of [FORMULA], falling into the central regions of a cluster of galaxies taking account of dynamical friction. We calculate the evolution of the expansion parameter, a(t), of the perturbation using a coefficient of dynamical friction, [FORMULA], calculated for a perturbation in which clustering is absent and a coefficient [FORMULA] obtained from a clustered one. The effect of the dynamical friction is to slow down the collapse (V. Antonuccio-Delogu & S. Colafrancesco 1994, hereafter AC) producing an observable variation of the parameter of expansion of the shell. The effect increases with increasing [FORMULA] and with the increasing of clustering. Finally, we show how the collapse time depends on [FORMULA] and [FORMULA].

Key words: cosmology: theory – galaxies: formation

Send offprint requests to: A.  Del Popolo, M.  Gambera

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998