Fossil clusters and understanding the structure formation

Fossil galaxy groups and clusters are thought to have formed relatively early and hence expected to have preserved crucial information that would otherwise be jost in the hierarchical destruction . I will introduce fossil systems and present evidences to show that they are different from non-fossil systems in their evolutionary history, using both observations and simulations.Observational studies are based on combined optical and X-ray observation including photometric and spectroscopic measurements.These studies show various systematic differences compared to non-fossil systems in their dominat galaxy properties and dark matter content of the derived from X-ray emissions of the inter-galactic medium allawing the probe of modela of galaxy and structure formation . High mass concentration of the fossil halos,the correlation of halo sub-structure fraction and galaxy luminosity gap , as well as thenin – boxy nature of the central galaxy isophotes in fossils.We use this constraints to test the available semi-analytic models of galaxy formation and study halo mass evolution of the fossils and non-fossil systems.