systems.
N-body simulations have been widely used over the last
decade as a standard tool to study the birth and growth of large scale
structure, clusters and galaxies. This approach has dealt, until
recently, with the forward integration in time of a set of
collisionless particles. Although what we observe directly is the
luminous matter
distribution , a proper hydrodynamical treatment of the baryonic
component
has not received much attention in the past, most because of the lack
of computing power.
The situation has began to change in the last few
years. Several techniques have been used to simulate the
evolution
of the gaseous component. The classical approach is the Eulerian one.
An alternative scheme is the smoothed - particle - hydrodynamics
( SPH ), which is a Lagrangian method with each particle
carrying information about the fluid element. The
code that I use is based on the SPH technique. In this
code the gravitational N-body system is solved using a hierarchical
tree algorithm. The TREESPH has been used in a range of
astrophysical problems, like formation and evolution of cluster of
galaxies, formation of galaxies,and the formation of damped Lyman- systems.
A parallel version
of the code
has been developed recently [5], that will allow to model with highly
improved dynamical range the evolution of cosmologically relevant
structure.
A long-term research project
is in progress in which large sets of TREESPH
simulations are used to investigate the
dependence of cluster X-ray properties of the simulated samples on the
background cosmological model, as well as
the numerical resolution of the simulations and the assumed model for
the physical gas processes.
Using the numerical samples the global morphology of galaxy clusters
and its evolution can be compared against X-ray data.
The internal dynamical state
of galaxy clusters is a function of
the global cosmological density parameter 
m and is connected to the amount
of observed substructures. Therefore a
promising way to constrain the cosmological models arises from the
study of substructures in the inner mass distribution [1]. This
approach has observational support both from internal galaxy
distribution and from X--ray image brightness.
Another issue, which
is closely related to the
amount of substructure in clusters, is the evolution of cluster
morphology with redshit. For three different
cosmological models, a simulation sample of 40 clusters was
generated from hydrodynamical SPH simulations and used to
investigate the cluster morphological
evolution out to
z=0.4 [2].
In
order to quantify the cluster
morphology we used Minkowski functionals, which are
defined in terms of 2+1 measures applied to cluster X-ray maps. The
cluster dynamical state is described using global cluster parameters
which obey fundamental plane relations such as
$M_vr_h^{\alpha}T_v^{\beta}=const$.
Works in progress on X-ray clusters are :
0, the preheating of the ICM due to SNe and
the
global metallicity of the universe at high redshift.Related Publications:
CDM and CHDM
models , New Astr., 4, 79