tokens: Figure 8. Galaxy stellar mass function at z = 0 for simulations with different black hole feedback parameters, including (i) no feedback (grey), (ii) v out = 10 3 km s −1 and (blue; fiducial simulation), (iii) v out = 10 4 km s −1 and (green), and (iv) v out = 10 3 km s −1 and (red). Error bars show cosmic variance estimates computed as the standard deviation over the eight sub-octants of the simulated volume. Black points connected by a dashed line show the observed stellar mass function from Baldry et al. ( 2012 ). Quasar mode feedback alone is not sufficient to reproduce the observed galaxy mass function, either at low or high masses. 4.4 Mass dependence of black hole feedback effects Fig. 9 shows in more detail how the effects of black hole feedback depend on galaxy stellar mass. We cross-match galaxies between simulations based on the unique ID of the particles they contain at z = 0. Each galaxy is matched to the galaxy that contains the largest number of common star particles, which we use to compute the stellar mass of galaxies in simulations with black hole feedback relative to the no-feedback simulation. Figure 9. Mass-dependent effects of galaxy-scale black hole feedback. Left: ratio of the stellar mass of galaxies at z = 0 in simulations including black hole feedback to the stellar mass of the corresponding galaxies in the no-feedback simulation as a function of stellar mass. Different colours indicate simulations with different outflow velocity and momentum flux. Solid lines and shaded regions indicate median and 10 per cent–90 per cent percentile ranges. Right: same as left for black hole masses. Black hole feedback appears to be more effective in galaxies with mass M ⋆ ∼ 10 10 M ⊙ for outflows with velocity v out = 10 3 km s −1 , while the mass suppression efficiency increases to higher mass galaxies for simulations with v out = 10 4 km s −1 . The overall effect of feedback on the growth of black holes and galaxies is qualitatively similar. Black hole feedback in our simulations with v out = 10 3 km s −1 is more effective at suppressing star formation and black hole growth in galaxies in the mass range M ⋆ ≈ 10 9 –10 11 M ⊙ at z = 0. This trend with M ⋆ , already present at z = 2, suggests that black holes in lower mass galaxies have not coupled enough energy to affect their host galaxies from the time of seeding down to z = 0 (which may be sensitive to our seed model), while outflows with v out = 10 3 km s −1 may not be sufficient to unbind gas in galaxies at the highest masses. With the same momentum flux and v out = 10 4 km s −1 , the results are similar at low M * but the mass suppression efficiency keeps increasing towards high masses, giving a ∼60 per cent reduction of the stellar mass of galaxies with M ⋆ ≳ 10 11.5 M ⊙ by z = 0. As expected, our simulation with v out = 10 3 km s −1 and yields the strongest suppression of stellar growth at all masses, but the efficiency follows a trend with M ⋆ similar to that of the
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