Intracluster stars in simulations with AGN feedback 7 the simulations are larger than those from Lin et al. (2003). However, they are roughly consistent with the Giodini et al. (2009) results there. When AGN feedback is included the combined stellar mass of the cluster galaxies drops by about ∼ 40%. This substantially improves the agreement with ob- servations for massive clusters. On the group scale, there is then good agreement with the Lin et al. (2003) data, while Giodini et al. (2009) inferred slightly larger mass fractions there. Overall, the stellar mass fractions obtained without AGN feedback are clearly too large. When the effects of AGN heating are included, the stellar mass in cluster galax- ies becomes however almost consistent with observations. In particular, the total stellar mass, i.e. including the ICL, agrees with the Gonzalez et al. (2007) results on the group scale. However, for massive clusters, we find a much larger ICL contribution in the simulations than they infer from ob- servations. The simulations also do not fully reproduce the observed strong trend of the stellar mass fractions with halo mass. One should mention that we did not include kinetic supernova feedback in the present set of simulations, in- stead all feedback from star formation was injected ther- mally. Using supernova feedback that includes a kinetic component can significantly reduce the amount of stars formed in hydrodynamical cosmological simulations (e.g Springel and Hernquist 2003b; Borgani et al. 2006). While this might help to reproduce the overall stellar mass frac- tions in massive clusters, it is, considering that such simu- lations (see Borgani et al. 2006) also find only a weak trend of stellar mass fractions with halo mass, unlikely to signif- icantly improve the overall agreement with observations. 5 Nevertheless, we repeated the simulation of one of our clus- ters, this time including a strong kinetic supernova feedback component, 6 in order to assess how it changes the fraction of stars found in the BCG, the ICL, and in the satellite galax- ies. This run also included AGN feedback. Its results are indicated by orange symbols in Fig. 5. The corresponding simulation without winds, is the one indicated by the red symbols at almost the same (slightly lower) M crit $_{500}$. In the following, we discuss what fraction of stars in our sim- ulated clusters and groups reside in the BCG, the ICL, and in the satellite galaxies, and how this compares to observa- tions. Fig. 6 shows the mass fractions of the stars found in the BCG and in the whole main halo, i.e. in the BCG+ICL component. The values were calculated within r crit $_{500}$. Results obtained from simulations both with and without AGN are shown. The BCG fractions are reported for all the four different methods we used to determine a BCG mass (see Sect. 2.2). For reference, observational constraints on the BCG+ICL luminosity fraction from Gonzalez et al. (2007) are also shown. They should be compared to the simulated BCG+ICL luminosity fractions indicated in the plot. The latter were computed within a projected radius (rather than a 3D radius) of r crit $_{500}$, using the same method to obtain stellar luminosities as described in Sect. 2.2. Without AGN, we obtain BCG+ICL fractions of roughly ∼ 50% for massive clusters, and of about ∼ 70% for groups. Note, however, that these values are sensitive to the radius inside which they are measured, because the dis- tribution of the BCG+ICL component is more concentrated than the distribution of the satellite galaxies. For example, within r crit 200 the values drop to about ∼ 45% and ∼ 65%, respectively. Accordingly, the BCG+ICL fractions are also lower when calculated within a projected radius rather than a 3D radius equal to r crit $_{500}$. However, the BCG+ICL lumi- nosity fractions indicated in the figure are also affected by small differences in the mass-to-light ratio. Namely, we find mass-to-light ratios for the BCG+ICL components that are a few percent smaller (up to 10% smaller for massive clus- ter, while being almost identical for groups) than those of the whole stellar population in the simulated halo. Thus, the c ○ 0000 RAS, MNRAS 000 , 000–000 GLYPH<BC>GLYPH<BA>GLYPH<BC>GLYPH<BD> GLYPH<BC>GLYPH<BA>GLYPH<BD> 10 13 10 14 10 15 GLYPH<D1>GLYPH<CP>GLYPH<D7>GLYPH<D7> GLYPH<CU>GLYPH<D6>GLYPH<CP> GLYPH<D8>GLYPH<CX>GLYPH<D3>GLYPH<D2>$^{GLYPH<DB>GLYPH<CX>GLYPH<D8>GLYPH<CW>GLYPH<CX>GLYPH<D2>}$ r  GLYPH<D6>GLYPH<CX>GLYPH<D8> GLYPH<BH>GLYPH<BC>GLYPH<BC> M  GLYPH<D6>GLYPH<CX>GLYPH<D8> GLYPH<BH>GLYPH<BC>GLYPH<BC> [ M ⊙ /h ] Ω$_{b}$ / Ω$_{m}$ GLYPH<BZ>GLYPH<D3>GLYPH<D2>GLYPH<DE>GLYPH<CP>GLYPH<D0>GLYPH<CT>GLYPH<DE> GLYPH<CT>GLYPH<D8> GLYPH<CP>GLYPH<D0>GLYPH<BA> GLYPH<B3>GLYPH<BC>GLYPH<BJ> GLYPH<BZ>GLYPH<CX>GLYPH<D3> GLYPH<CS>GLYPH<CX>GLYPH<D2>GLYPH<CX> GLYPH<CT>GLYPH<D8> GLYPH<CP>GLYPH<D0>GLYPH<BA> GLYPH<B3>GLYPH<BC>GLYPH<BL> GLYPH<C4>GLYPH<CX>GLYPH<D2> GLYPH<CT>GLYPH<D8> GLYPH<CP>GLYPH<D0>GLYPH<BA> GLYPH<B3>GLYPH<BC>GLYPH<BF> GLYPH<CQ>GLYPH<CP>GLYPH<D6>GLYPH<DD> GLYPH<D3>GLYPH<D2>GLYPH<D7>GLYPH<B8> GLYPH<D2>GLYPH<D3> GLYPH<BT> GLYPH<BZ>GLYPH<C6> GLYPH<CQ>GLYPH<CP>GLYPH<D6>GLYPH<DD> GLYPH<D3>GLYPH<D2>GLYPH<D7>GLYPH<B8> GLYPH<DB>GLYPH<CX>GLYPH<D8>GLYPH<CW> GLYPH<BT> GLYPH<BZ>GLYPH<C6> GLYPH<CP>GLYPH<D0>GLYPH<D0> GLYPH<D7>GLYPH<D8>GLYPH<CP>GLYPH<D6>GLYPH<D7>GLYPH<B8> GLYPH<D2>GLYPH<D3> GLYPH<BT> GLYPH<BZ>GLYPH<C6> GLYPH<CP>GLYPH<D0>GLYPH<D0> GLYPH<D7>GLYPH<D8>GLYPH<CP>GLYPH<D6>GLYPH<D7>GLYPH<B8> GLYPH<DB>GLYPH<CX>GLYPH<D8>GLYPH<CW> GLYPH<BT> GLYPH<BZ>GLYPH<C6> GLYPH<CV>GLYPH<CP>GLYPH<D0>GLYPH<CP>GLYPH<DC>GLYPH<CX>GLYPH<CT>GLYPH<D7>GLYPH<B8> GLYPH<D2>GLYPH<D3> GLYPH<BT> GLYPH<BZ>GLYPH<C6> GLYPH<CV>GLYPH<CP>GLYPH<D0>GLYPH<CP>GLYPH<DC>GLYPH<CX>GLYPH<CT>GLYPH<D7>GLYPH<B8> GLYPH<DB>GLYPH<CX>GLYPH<D8>GLYPH<CW> GLYPH<BT> GLYPH<BZ>GLYPH<C6> Figure 5. Mass fraction of baryons ( circles ), all stars (including ICL, squares ), and stars residing in galaxies ( triangles ) within r crit 500 for clusters and groups simulated with and without AGN feedback. The latter was found by summing up the stellar masses of the BCG, which was found by Method 1 , and all satellite galax- ies within r crit $_{500}$. Observational data are shown for comparison. The Gonzalez et al. (2007) data should be compared to the mass fraction of all stars, while the other observational data should be compared to the mass fraction of stars found in galaxies. The cosmic baryon fraction assumed in the simulations is shown for reference. The orange symbols show results of a simulation where also kinetic supernova feedback was included. 3.1.2 The stellar fractions in the BCG, ICL, and satellite galaxies 5 Recently, more sophisticated kinetic supernova feedback schemes that tune the wind velocity and mass loading fac- tor to properties of the host galaxy have been suggested (Oppenheimer and Dav´ e 2006; Okamoto et al. 2009). Such mod- els might be more successful in reproducing a strong trend of the stellar mass fraction with halo mass. 6 We assumed a supernova wind velocity of ∼ 480 km/s and a wind mass flux rate that equals twice the star formation rate (for details of the wind model see Springel and Hernquist 2003a)