Tidal torques and the clusters of galaxies evolution

TL;DR

This paper investigates how tidal torques influence the collapse timing and mass accumulation of galaxy clusters, revealing their role in biasing structure formation and aligning with observed cluster-scale biases.

Contribution

It introduces a model incorporating tidal torques into collapse dynamics, showing their impact on mass bias and cluster formation in a Cold Dark Matter universe.

Findings

Tidal torques delay collapse in high-density environments.

Bias in mass distribution arises from delayed collapse due to tidal effects.

The model's bias estimates align with observational data on cluster scales.

Abstract

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 \nu 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 bias can account for a substantial part of the total bias required by observations on cluster scales.