Speaker
Neven Tomicic
(MPIA)
Description
Galaxy clusters are large virialized collections of galaxies. Galaxies contribute about 5% to the mass of the cluster, the intracluster medium about 10% and the dark matter up to 85%. These structures are formed from galaxy protoclusters. A protocluster is an early type of clusters with fewer galaxies and an observed higher number densities of galaxies, compared to other parts of the observed sky. The goal of this paper is to simulate galaxy protoclusters at different redshifts (z=2,3,4,5). using Monte Carlo simulations, following the predefined surface profiles of the protoclusters and taking into account the errors of photometric redshift (versus spectroscopic redshifts) specifically for the COSMOS survey. By simualting 1000 different types of protoclusters (Virgo, Coma and Fornax), we quantified the characteristics of the search methods of protoclusters in the COSMOS, such as completeness (a number that defines the share of galaxies derived after search methods , compared to the total numbers of galaxies in the protoclusters), contamination (a number that defines the share of galaxies in the sky that does not belong to the protocluster), number density and effective radius (radius within which there is 68% of the mass of protocluster) and their behaviour for different types and redshifts. The results show that completeness of the protoclusters does not change compared to the redshift, while contamination increases with the distance from the centre of PC. The calculated effective radii of our simulated PCs agree within the factor 2 with the initial radii calculated by Chiang et al. (2013). Despite the discrepancy within our effective radii, 55-65% of galaxies are in protoclusters, which is consistent with the results of Chiang et al. (2013). We believe that the differences between the radii are caused by the fact that our simulations do not take into account the distribution of the mass in the protoclusters. We assumed that all galaxies have the same mass, which can significantly affect the calculations of effective radius. In the end we applied the search methods of protoclusters and the method of calculating the effective radius to existing protoclusters in COSMOS field, at different redshifts.