The evolution of an intra-cluster and intra-group stellar population
Their contribution to the stellar mass, their age, and their dynamics
Institute for Astro- and Particle Physics, University
of Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria e-mail: email@example.com
2 Departamento de Física Teórica, Modulo C-XI, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Cantoblanco, Madrid, Spain
3 ESO, Karl-Schwarzschild-Strasse 2,85748 Garching bei Muenchen, Germany
Accepted: 30 March 2010
Aims. We investigate the properties of an intra-cluster stellar population (ICSP) and an intra-group stellar population (IGSP) as a function of time. We apply different criteria to separate between the stellar components residing in the galaxies and in the intergalactic spaces. In addition we investigate the rate of SNIa events in the ICSP/IGSP and the amount of 56Fe produced by these events. Finally we compare the dynamics of the ICSP/IGSP with the stellar component residing in the galaxies.
Methods. By applying a combined N-body/hydrodynamic description (GADGET-2) with radiative cooling and a recipe for star formation and stellar feedback two different sized systems were calculated, i.e. galaxy cluster and galaxy groups. From these simulations extended halo catalogues were extracted with AHF: Amiga's Halo Finder. Together with the full information of all particles in the simulation several separation criteria between the ICSP/IGSP and the stellar component in the galaxies were investigated in detail.
Results. Applying different criteria to distinguish the stellar components inside and outside clusters/groups reveals different 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 simulation depending on the applied separation criteria at redshift z=0. The same separation criteria applied on a group simulation results in a 3% to 30% IGSP component compared to the total stellar mass in the system at redshift z = 0. Our investigation reveals a major difference between the gradient in the evolution of the ICSP and IGSP; the stellar mass present in the ICSP is increasing, whereas the fraction of stellar mass in the IGSP is decreasing in the same redshift regime. Applying simple SNIa rate estimates yields SNIa rates for the ICSP/IGSP of the order of 0.05 SNIa events per year in the ICSP and one order of magnitude lower for the IGSP, reflecting the different stellar masses in the ICSP/IGSP. The amount of 56Fe-mass produced by the ICSP/IGSP SNIa is nearly two orders of magnitudes lower than observed values. The mean age of the stellar component populating the ICSP/IGSP is younger than the mean age of the stellar component in the galaxies. The maximum in the velocity distribution of the ICSP is shifted to lower velocities compared to the maximum in the velocity distribution of the stellar component in the galaxy cluster simulation. This reflects the high galaxy interaction rate present in the galaxy clusters. The difference gives us a measure for the dynamical state of the galaxy cluster/group.
Key words: methods: numerical / galaxies: interactions / galaxies: clusters: general / galaxies: general
© ESO, 2010