Large-scale tidal fields on primordial density perturbations ?

Abstract

We calculate the strength of the tidal field produced by the large-scale density field acting on primordial density perturbations in power law models. By analysing changes in the orientation of the deformation tensor, resulted from smoothing the density field on different mass scales, we show that the large-scale tidal field can strongly affect the morphology and orientation of density peaks. The measure of the strength of the tidal field is performed as a function of the distance to the peak and of the spectral index. We detected evidence that two populations of perturbations seems to coexist; one, with a misalignment between the main axes of their inertia and deformation tensors. This would lead to the angular momentum acquisition and morphological changes. For the second population, the perturbations are found nearly aligned in the direction of the tidal field, which would imprint them low angular momentum and which would allow an alignment of structures as those reported between clusters of galaxies in filaments, and between galaxies in clusters. Evidence is presented that the correlation between the orientation of perturbations and the large-scale density field could be a common property of Gaussian density fields with spectral indexes $n < 0$. We argue that alignment of structures can be used to probe the flatness of the spectrum on large scales but it cannot determine the exact value of the spectral index.