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Astron. Astrophys. 337, 96-104 (1998)

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Tidal torques and the clusters of galaxies evolution

A. Del Popolo 1, 2 and M. Gambera 1, 3

1 Istituto di Astronomia dell'Università di Catania, Viale A.Doria 6, I-95125 Catania, Italy
2 Facoltà di Ingegeneria, Università Statale di Bergamo, Piazza Rosate 2, I-24129 Bergamo, Italy
3 Osservatorio Astrofisico di Catania and CNR-GNA, Viale A.Doria 6, I-95125 Catania, Italy

Received 2 September 1997 / Accepted 2 February 1998


We study the effect of tidal torques on the collapse of density peaks through the equations of motion of a shell of barionic matter falling into the central regions of a cluster of galaxies. We calculate the time of collapse of the perturbation taking into account the gravitational interaction of the quadrupole moment of the system with the tidal field of the matter of the neighbouring proto-clusters. We show that within high-density environments, such as rich clusters of galaxies, tidal torques slow down the collapse of low-[FORMULA] peaks producing an observable variation in the time of collapse of the shell and, as a consequence, a reduction in the mass bound to the collapsed perturbation. Moreover, the delay of the collapse produces a tendency for less dense regions to accrete less mass, with respect to a classical spherical model, inducing a biasing of over-dense regions toward higher mass. Finally we calculate the bias coefficient using a selection function properly defined showing that for a Standard Cold Dark Matter (SCDM) model this [FORMULA] can account for a substantial part of the total bias required by observations on cluster scales.

Key words: cosmology: theory – cosmology: large scale structure of Universe – galaxies: formation

Send offprint requests to: M. Gambera, (mga@sunct.ct.astro.it)

© European Southern Observatory (ESO) 1998

Online publication: August 6, 1998