Dark matter and structure formation a review

This paper provides a review of the variants of dark matter which are thought to be fundamental components of the universe and their role in origin and evolution of structures and some new original results concerning improvements to the spherical collapse model. In particular, I show how the spherical collapse model is modified when we take into account dynamical friction and tidal torques.

Some improvements to the spherical collapse model

I study the joint effect of dynamical friction, tidal torques and cosmological constant on clusters of galaxies formation I show that within high-density environments, such as rich clusters of galaxies, both dynamical friction and tidal torques slows down the collapse of low-? peaks producing an observable variation in the time of collapse of the perturbation 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 I show how the threshold of collapse is modified if dynamical friction, tidal torques and a non-zero cosmological constant are taken into account and I use the Extended Press Schecter (EPS) approach to calculate the effects on the mass function Then, I compare the numerical mass function given in Reed et al (2003) with the theoretical mass function obtained in the present paper I show that the barrier obtained in the present paper gives rise to a better description of the mass function evolution with respect to other previous models (Sheth & Tormen 1999, MNRAS, 308, 119 (hereafter ST); Sheth & Tormen 2002, MNRAS, 329, 61 (hereafter ST1))