6 Ewald Puchwein, Volker Springel, Debora Sijacki, & Klaus Dolag ter stars is remarkably insensitive to the detailed parameters of the star formation model. We now turn to the presentation of our primary results, obtained by applying the methods introduced in Sect. 2.2 to our full sample of simulated clusters. 4 In particular, we investigate what fraction of a cluster’s stellar mass resides in the BCG, the ICL, and in the satellite galaxies. We also study whether the answer to this question depends on cluster mass. Finally, we examine where the stars that end up in these three components at redshift z = 0 are formed, and in what objects they fall into the cluster. Figure 5 illustrates the baryon and stellar mass fractions of our simulated clusters, as well as the mass fraction of stars that reside in cluster galaxies as a function of cluster mass M crit $_{500}$. Results from simulations both with and without AGN feedback are shown, and for comparison with observational constraints, data from Gonzalez et al. (2007), Giodini et al. (2009) and Lin et al. (2003) are included. old density for star formation by a factor of ∼ 4 compared to the original simulation. Within the subresolution model of Springel and Hernquist (2003a) for the regulation of star formation this was achieved by increasing the ‘supernova temperature’ T SN from 10 $^{8}$K to 4 × 10 $^{8}$K, as well as the supernova evaporation factor A 0 from 1000 to 4000, while keeping the gas consumption timescale the same. However, the analysis of this simulation yielded very similar results to the original run. The fraction of stars in the BCG+ICL component changed by only about 1%. Varying instead the timescale for star formation and thereby shifting the peak of the star formation activity to a different stage in the assembly history of the cluster might also affect the ICL component. In particular, since merg- ers play an important role in liberating stars from their host galaxies (see Murante et al. 2007), the efficiency of this mechanism for creating ICL stars may depend on the star formation history of the cluster. The idea behind our sec- ond test of the star formation model was therefore to in- crease the timescale t ∗ 0 for the conversion of gas into stars from 2.1 Gyrs to 8.4 Gyrs. Keeping everything else equal, this required again to set T SN = 4 × 10 $^{8}$K and A 0 = 4000 to leave the gas density threshold at its original value, while t ∗ 0 itself was increased by a factor of 4. Using this larger gas consumption timescale indeed shifts the peak of the star for- mation history to much later times and broadens it at the same time. It also results in more star formation at low red- shift. However, also for this simulation we find remarkably little difference in the galaxy population and the ICL com- pared to the original run. Despite the substantial change in the star formation history, the fraction of stars in the BCG+ICL component increased by only 4%. Overall, these tests show that the fraction of stars that get unbound from their host galaxies and become intraclus- Also shown in Fig. 5 is the mass fraction of stars in cluster galaxies. More precisely, these values were calculated by summing up the stellar masses of the BCG, which was found by Method 1 , i.e. using the radial cut-off scaled with the cluster mass, and of all satellite galaxies within r crit $_{500}$. The resulting values can be compared to the mass fractions of stars in cluster galaxies obtained by Giodini et al. (2009) and Lin et al. (2003). Without AGN, we again find a sig- nificant discrepancy for massive clusters. Compared to the observations the combined stellar mass of the cluster galax- ies is too large. Also on the group scale the mass fractions in Without AGN, we obtain very large stellar mass frac- tions. In massive clusters, roughly 40% of the baryonic mass is found in stars, while on the group scale this number rises to about 60%. This seems to be inconsistent with obser- vations, especially for massive clusters. When AGN are in- cluded, the stellar mass fractions within r crit 500 are lowered by about one third. One can compare these total stellar mass fractions to the constraints from Gonzalez et al. (2007), as both cluster galaxies and intracluster stars were accounted for in that study. The simulated and observed stellar mass fractions are in good agreement on the group scale. However, we do not find a comparably strong trend with halo mass in our simulations as inferred by Gonzalez et al. (2007), and accordingly we obtain significantly larger stellar mass frac- tions for massive clusters. In the simulations without AGN feedback, the baryon mass fractions within r crit 500 differ by less than ∼ 10% from the assumed cosmic baryon fraction. When AGN are included, this holds only for the most massive clusters, while there is a significant baryon depletion in poor clusters and groups due to the AGN heating (see also Puchwein et al. 2008). 3.1 Intracluster light, satellite galaxies, and BCGs in simulations and observations 3.1.1 The baryonic mass fractions 3 RESULTS 4 Unless indicated otherwise, we use the redshift z = 0 outputs. c ○ 0000 RAS, MNRAS 000 , 000–000 Figure 4. Combined stellar mass of all satellite galaxies with individual stellar masses exceeding M as a function of galaxy stellar mass M . Results are shown for zoom factor 1, 2 and 3 simulations of a M crit 200 = 1 . 5 × 10 14 h − 1 M$_{⊙}$ cluster and zoom factor 3 and 4 simulations of a M crit 200 = 3 × 10 13 h − 1 M$_{⊙}$ group. No AGN have been included in these runs. The vertical lines, arrows and, labels (zf1) , (zf2) , and (zf3) indicate the galaxy mass ranges in which the stellar mass in satellite galaxies is approximately converged in zoom factor 1, 2, and 3 simulations, respectively. 10 12 10 13 10 9 10 10 11 10 12  GLYPH<D9>GLYPH<D1> GLYPH<D9>GLYPH<D0>GLYPH<CP>GLYPH<D8>GLYPH<CX>GLYPH<DA> GLYPH<CT> GLYPH<D7>GLYPH<D8>GLYPH<CT>GLYPH<D0>GLYPH<D0>GLYPH<CP>GLYPH<D6>$^{GLYPH<D1>GLYPH<CP>GLYPH<D7>GLYPH<D7>}$$^{GLYPH<D3>GLYPH<CU>}$ GLYPH<D7>GLYPH<CP>GLYPH<D8>GLYPH<CT>GLYPH<D0>GLYPH<D0>GLYPH<CX>GLYPH<D8>GLYPH<CT> GLYPH<CV>GLYPH<CP>GLYPH<D0>GLYPH<CP>GLYPH<DC>GLYPH<CX>GLYPH<CT>GLYPH<D7>$^{GLYPH<CJ>}$ M ⊙ /h$^{℄}$ GLYPH<CV>GLYPH<CP>GLYPH<D0>GLYPH<CP>GLYPH<DC>GLYPH<DD> GLYPH<D7>GLYPH<D8>GLYPH<CT>GLYPH<D0>GLYPH<D0>GLYPH<CP>GLYPH<D6> GLYPH<D1>GLYPH<CP>GLYPH<D7>GLYPH<D7> GLYPH<C5> GLYPH<CJ> M ⊙ /h ℄ GLYPH<B4>GLYPH<DE>GLYPH<CU>GLYPH<BD>GLYPH<B5> GLYPH<B4>GLYPH<DE>GLYPH<CU>GLYPH<BE>GLYPH<B5> GLYPH<B4>GLYPH<DE>GLYPH<CU>GLYPH<BF>GLYPH<B5>  GLYPH<D0>GLYPH<D9>GLYPH<D7>GLYPH<D8>GLYPH<CT>GLYPH<D6>GLYPH<B8> GLYPH<DE>GLYPH<BA> GLYPH<CU>GLYPH<BA> GLYPH<BD>  GLYPH<D0>GLYPH<D9>GLYPH<D7>GLYPH<D8>GLYPH<CT>GLYPH<D6>GLYPH<B8> GLYPH<DE>GLYPH<BA> GLYPH<CU>GLYPH<BA> GLYPH<BE>  GLYPH<D0>GLYPH<D9>GLYPH<D7>GLYPH<D8>GLYPH<CT>GLYPH<D6>GLYPH<B8> GLYPH<DE>GLYPH<BA> GLYPH<CU>GLYPH<BA> GLYPH<BF> GLYPH<CV>GLYPH<D6>GLYPH<D3>GLYPH<D9>GLYPH<D4>GLYPH<B8> GLYPH<DE>GLYPH<BA> GLYPH<CU>GLYPH<BA> GLYPH<BF> GLYPH<CV>GLYPH<D6>GLYPH<D3>GLYPH<D9>GLYPH<D4>GLYPH<B8> GLYPH<DE>GLYPH<BA> GLYPH<CU>GLYPH<BA> GLYPH<BG>