Nonlinear dynamics and mass function of cosmic structures. I. Analytical results.
Abstract
We investigate some modifications to the Press & Schechter (1974) (PS) prescription resulting from shear and tidal effects. These modifications rely on more realistic treatments of the collapse process than the standard approach based on the spherical model. First, we show that the mass function resulting from a new approximate Lagrangian dynamic, contains more objects at high mass, than the classical PS mass function and is well fitted by a PSlike function with a threshold density of δ_c_=~1.4. However, such a Lagrangian description can underestimate the epoch of structure formation since it defines it as the collapse of the first principal axis. We therefore suggest some analytical prescriptions, for computing the collapse time along the second and third principal axes, and we deduce the corresponding mass functions. The collapse along the third axis is delayed by the shear and the number of objects of high mass then decreases. Finally, we show that the shear also strongly affects the formation of lowmass halos. This dynamical effect implies a modification of the lowmass slope of the mass function and allows the reproduction of the observed luminosity function of field galaxies. In a companion paper, we present results of numerical simulations which complete this work.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 September 1997
 arXiv:
 arXiv:astroph/9704023
 Bibcode:
 1997A&A...325..439A
 Keywords:

 COSMOLOGY: THEORY;
 GRAVITATION;
 LARGESCALE STRUCTURE OF UNIVERSE;
 Astrophysics
 EPrint:
 12 pages, latex 2e, accepted for publication in Astronomy &