Research Overview

The current cosmological model successfully accounts for the global features of the universe, such as the spatial distribution of mass in the universe, but apparently fails below cluster scales. The results of current simulations still disagree with observational data, particularly so for the cores of clusters. The discrepancy is apparent when comparing observed and predicted scaling relations, such as the luminosity-temperature relation, entropy-temperature relation, and the mass-temperature relation. Other intracluster (IC) gas properties, such as higher chemical elements (hereafter metallicity) distribution, entropy and - most notably - the central mass profile, especially the prediction of a cusp in the DM density in the inner core, are also in conflict with observational results. Unexplained features on galactic scales include high predicted numbers of small satellite systems around giant galactic halos, and low angular momentum and the consequent small size of galactic disks. Moreover, both theoretical models and numerical results significantly overpredict the observed stellar mass density at early times.

I argue that these differences can be a consequence of incorrect modeling of the star formation history, and lack of essential physical processes in semi-analytical models and simulations. Thus, in the current research I will test the effects of implementing the essential physical processes that occur in the cluster galaxies and in IC gas, combined with higher and more realistic star formation rates at early times, on the properties of clusters of galaxies and their basic statistical scaling relations.

My basic idea is to model the galaxies in the cluster as basic constructs (galcons) with an extended distribution. Then, by using semi-analytic models for the physical phenomena in those galaxies, I will be able to describe the global mass and energy feedback from galaxies to the IC gas, instead of calculating the feedback from each individual star. This simplification will substantially reduce the required computational resources without affecting the total mass distribution, therefore increasing the simulation spatial resolution. The main benefit will be the attainment of a higher level of spatial resolution and a more detailed and complete description of the interactions between the galaxies, DM and gas. Furthermore, the necessary physical processes can be easily implemented in the code using semi-analytic models, and it will also be possible to generate relatively long episodes of star formation in these galaxies, as seen in recent observations. All these modifications will be implemented in a powerful cosmological hydrodynamical simulation code.

Physical processes that will be studied in this research, such as outflows of energy and mass from stellar explosions, large amount of gas stripped from the cluster galaxies, dynamical friction between the galaxies, gas and DM, will strongly affect the properties of IC gas. Previous studies which ignored these processes, obviously enhanced the discrepancy with observations. Furthermore, different levels of activity, combination, and duration of these processes will shape IC gas in different ways. Therefore, I hope to be able to draw some conclusions about the strength and effectiveness of these processes on cluster properties.

It is anticipated that our planned simulation and comprehensive analysis work will lead to an improved description of the physical phenomena in galaxies and clusters, and to better insight on the history of star formation in galaxies. This will enhance our understanding of the large scale structure of the universe and the detailed properties of the largest (physically bound) systems – clusters of and galaxies.