The evolution of an intra-cluster and intra-group stellar population - Their contribution to the stellar mass, their age, and their dynamics

摘要

Aims. We investigate the properties of anintra-cluster stellar population (ICSP) and an intra-group stellarpopulation (IGSP) as a function of time. We apply different criteria toseparate between the stellar components residing in the galaxies and inthe intergalactic spaces. In addition we investigate the rate of SNIaevents in the ICSP/IGSP and the amount of 56Feproduced by these events. Finally we compare the dynamics of theICSP/IGSP with the stellar component residing in the galaxies. Methods. By applying a combined N-body/hydrodynamicdescription (GADGET-2) with radiative cooling and a recipe for starformation and stellar feedback two different sized systems werecalculated, i.e. galaxy cluster and galaxy groups. From thesesimulations extended halo catalogues were extracted with AHF: Amiga'sHalo Finder. Together with the full information of all particles in thesimulation several separation criteria between the ICSP/IGSP and thestellar component in the galaxies were investigated in detail. Results. Applying different criteria to distinguishthe stellar components inside and outside clusters/groups revealsdifferent amounts of stellar mass present in the ICSP. We find that 7%to 40% of all stars belong to the ICSP in the galaxy cluster simulationdepending on the applied separation criteria at redshift z=0.The same separation criteria applied on a group simulation results in a3% to 30% IGSP component compared to the total stellar mass in thesystem at redshift z=0. Our investigation reveals amajor difference between the gradient in the evolution of the ICSP andIGSP; the stellar mass present in the ICSP is increasing, whereas thefraction of stellar mass in the IGSP is decreasing in the same redshiftregime. Applying simple SNIa rate estimates yields SNIa rates for theICSP/IGSP of the order of 0.05 SNIa events per year in the ICSP and oneorder of magnitude lower for the IGSP, reflecting the different stellarmasses in the ICSP/IGSP. The amount of 56Fe-massproduced by the ICSP/IGSP SNIa is nearly two orders of magnitudes lowerthan observed values. The mean age of the stellar component populatingthe ICSP/IGSP is younger than the mean age of the stellar component inthe galaxies. The maximum in the velocity distribution of the ICSP isshifted to lower velocities compared to the maximum in the velocitydistribution of the stellar component in the galaxy cluster simulation.This reflects the high galaxy interaction rate present in the galaxyclusters. The difference gives us a measure for the dynamical state ofthe galaxy cluster/group. Key words: methods: numerical - galaxies:interactions - galaxies: clusters: general - galaxies: general