that were inspired by observational approaches, i.e. between Method 1 , where a radial cut-off is used, and Method 2 , where surface brightness profiles are analyzed. Also, the methods that rely on the dynamics, i.e. Method 3 and Method 4 , usu- ally agree well with each other, even though this is perhaps not too surprising as they both are based on the same fit of the stellar velocity distribution. In the rare cases were they do disagree, it is typically in unrelaxed objects, e.g. when an infalling group perturbs the stellar velocity distribution and prevents an accurate two-component Maxwell fit. Overall, there is hence some uncertainty in the BCG mass due to the choice of the analysis method used for sep- arating the BCG from the ICL. However, for all our differ- ent methods only a small part of the stars in the main halo, i.e. in the BCG+ICL component, may be assigned to the BCG. This also means that independent of how exactly we choose to make a distinction between BCG and ICL, we find a very significant ICL component in our simulated clusters and groups. We also note that the BCG and ICL compo- nents in Gonzalez et al. (2005) are defined very similarly to our Method 2 , hence our analysis method should yield results that can be directly compared to observations. The fraction of stars in the ICL can be read off form the difference between the BCG+ICL and BCG fractions in Fig. 6. As can be seen, the ICL fractions in our simulations are almost independent of the cluster mass. Within r crit $_{500}$, they are roughly ∼ 45% without AGN and ∼ 50% with AGN physics. If we go to the larger radius of r crit 200 instead, they are slightly lower, that is about ∼ 40% without AGN and ∼ 45% with AGN. At a first glance these findings seem to be at odds with the results of Murante et al. (2007), where an ICL frac- tion rising with cluster mass was found, from ∼ 15% at 10 $^{14}$h − $^{1}$M ⊙ to ∼ 30% at 10 $^{15}$h − $^{1}$M ⊙ . However, the lower values they obtained are most likely a consequence of the much lower numerical resolution in their simulations, as they explicitly exclude stars from the ICL that got liberated from poorly resolved galaxies. Looking only at the three clusters they have simulated at high resolution, i.e. with a mass reso- lution comparable to our simulations, there is no significant discrepancy. For those three objects they find ICL fractions of 37%, 28%, and 41%, and no strong indication of a depen- dence on cluster mass. i-band luminosity fractions are only slightly smaller than the mass fractions calculated within a 3D radius equal to r crit $_{500}$. When accounting for these effects, we nevertheless still ob- tain larger BCG+ICL fractions than derived from the ob- servations of Gonzalez et al. (2007), especially for massive clusters. When AGN feedback is included, the stellar mass of the BCG+ICL component decreases by about ∼ 25%. However, the total stellar masses decrease somewhat more strongly (see Fig. 5). Thus, we find even slightly larger BCG+ICL fractions in the simulations with AGN. A potential explana- tion for this effect is that galaxies falling into the cluster in simulations with AGN may be more prone to tidal disrup- tion due to their lower stellar mass and due to an expansion of their halos as a consequence of the removal of gas by AGN heating. Especially in the runs without AGN, there are several clusters for which all the four different analysis methods for identifying the BCG yield very similar BCG fractions and masses (see also Fig. 1). There are, on the other hand, also clusters where the results differ. In most of them, how- ever, there is still good agreement between the two methods Fig. 7 compares the surface brightness profiles of the BCG+ICL component in three of our simulated groups to observational constraints from Zibetti et al. (2005). For our simulated halos they were calculated for simulation outputs at redshift z = 0 . 21 of runs with and without AGN, scaled to the reference redshift of 0.25. 7 The profile from Zibetti et al. (2005) is a mean surface brightness profile obtained by stack- ing SDSS cluster and group images, with a mean halo mass of M mean 200 ≈ 7 − 8 × 10 $^{13}$M ⊙ . Also shown is the profile they ob- tain without assuming a correction for incompletely masked satellite galaxies. In the figure, we compare with the two sim- ulated groups from our sample whose mass M mean 200 is closest c ○ 0000 RAS, MNRAS 000 , 000–000 3.1.3 The radial distribution of BCG+ICL stars Figure 6. Fraction of the stellar mass within r crit 500 found in the BCG, and in the BCG+ICL component. Mass fractions are shown as a function of cluster mass M crit 500 and for the four different meth- ods of determining a BCG mass (see Sect. 2.2). The upper panel shows the values computed from runs without AGN, while the lower panel illustrates the results obtained when including the AGN feedback. Also shown is the BCG+ICL i-band luminosity fraction within a projected radius on the sky (rather than 3D ra- dius) of r crit $_{500}$. This data can be directly compared to the observed BCG+ICL luminosity fractions from Gonzalez et al. (2007). GLYPH<BC> GLYPH<BC>GLYPH<BA>GLYPH<BE> GLYPH<BC>GLYPH<BA>GLYPH<BG> GLYPH<BC>GLYPH<BA>GLYPH<BI> GLYPH<BC>GLYPH<BA>GLYPH<BK> GLYPH<BD> GLYPH<CU>GLYPH<D6>GLYPH<CP> GLYPH<D8>GLYPH<CX>GLYPH<D3>GLYPH<D2>$^{GLYPH<D3>GLYPH<CU>}$$^{GLYPH<D7>GLYPH<D8>GLYPH<CP>GLYPH<D6>GLYPH<D7>}$$^{GLYPH<B4>GLYPH<CU>GLYPH<D3>GLYPH<D6>}$ < r  GLYPH<D6>GLYPH<CX>GLYPH<D8> 500 GLYPH<B5> GLYPH<D2>GLYPH<D3> GLYPH<BT> GLYPH<BZ>GLYPH<C6> GLYPH<BC> GLYPH<BC>GLYPH<BA>GLYPH<BE> GLYPH<BC>GLYPH<BA>GLYPH<BG> GLYPH<BC>GLYPH<BA>GLYPH<BI> GLYPH<BC>GLYPH<BA>GLYPH<BK> GLYPH<BD> 10 13 10 14 10 15 M  GLYPH<D6>GLYPH<CX>GLYPH<D8> 500 [ M ⊙ /h ] GLYPH<DB>GLYPH<CX>GLYPH<D8>GLYPH<CW> GLYPH<BT> GLYPH<BZ>GLYPH<C6> 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<BE>GLYPH<BC>GLYPH<BC>GLYPH<BJ>GLYPH<B8> GLYPH<BU>GLYPH<BV>GLYPH<BZ>GLYPH<B7>GLYPH<C1>GLYPH<BV>GLYPH<C4> GLYPH<BU>GLYPH<BV>GLYPH<BZ>GLYPH<B7>GLYPH<C1>GLYPH<BV>GLYPH<C4>GLYPH<B8> GLYPH<D7>GLYPH<D8>GLYPH<CT>GLYPH<D0>GLYPH<D0>GLYPH<CP>GLYPH<D6> GLYPH<D1>GLYPH<CP>GLYPH<D7>GLYPH<D7> GLYPH<BU>GLYPH<BV>GLYPH<BZ>GLYPH<B7>GLYPH<C1>GLYPH<BV>GLYPH<C4>GLYPH<B8> GLYPH<CX>GLYPH<B9>GLYPH<CQ>GLYPH<CP>GLYPH<D2>GLYPH<CS>GLYPH<B8> GLYPH<CX>GLYPH<D2> GLYPH<D4>GLYPH<D6>GLYPH<D3> GLYPH<CY>GLYPH<BA> GLYPH<BU>GLYPH<BV>GLYPH<BZ>GLYPH<B8> GLYPH<C5>GLYPH<CT>GLYPH<D8>GLYPH<CW>GLYPH<BA> GLYPH<BD> GLYPH<BU>GLYPH<BV>GLYPH<BZ>GLYPH<B8> GLYPH<C5>GLYPH<CT>GLYPH<D8>GLYPH<CW>GLYPH<BA> GLYPH<BE> GLYPH<BU>GLYPH<BV>GLYPH<BZ>GLYPH<B8> GLYPH<C5>GLYPH<CT>GLYPH<D8>GLYPH<CW>GLYPH<BA> GLYPH<BF> GLYPH<BU>GLYPH<BV>GLYPH<BZ>GLYPH<B8> GLYPH<C5>GLYPH<CT>GLYPH<D8>GLYPH<CW>GLYPH<BA> GLYPH<BG> 7 The r 0 . $_{25}$-band of the photometric system defined in Zibetti et al. (2005) is used for this comparison. 8 Ewald Puchwein, Volker Springel, Debora Sijacki, & Klaus Dolag