The contribution of massive haloes to the matter power spectrum in the presence of AGN feedback

The clustering of matter, as measured by the matter power spectrum, informs us about dark matter and cosmology, as well as baryonic effects on the distribution of matter in the universe. Using cosmological hydrodynamical simulations from the cosmo-OWLS and BAHAMAS simulation projects, we investigate the contribution of power in haloes with various masses, defined by particles within some overdensity region, to the full power spectrum, as well as the power ratio between baryonic and dark matter only (DMO) simulations for a matched (between simulations) and an unmatched set of haloes. We find that the presence of AGN feedback suppresses the power on all scales for haloes of all masses examined ($10^{11.25}\leq M_{500,\mathrm{crit}}\leq 10^{14.75}\,\mathrm{M_\odot}/h$), by ejecting matter from within $r_{500,\mathrm{c}}$ to $r_{200,\mathrm{m}}$ and potentially beyond in massive haloes ($M_{500,\mathrm{crit}}\gtrsim 10^{13}\,\mathrm{M_\odot}/h$), and likely impeding the growth of lower-mass haloes as a consequence. A lower AGN feedback temperature drastically changes the behaviour of high-mass haloes ($M_{500,\mathrm{crit}}\geq 10^{13.25}\,\mathrm{M_\odot}/h$), damping the effects of AGN feedback at small scales, $k\,\gtrsim\,4\,h\mathrm{\,Mpc^{-1}}$. For $k\,\lesssim\,3\,h\mathrm{\,Mpc^{-1}}$, group-sized haloes ($10^{14\pm0.25}\, \mathrm{M_\odot}/h$) dominate the power spectrum, while on smaller scales the combined contributions of lower-mass haloes to the full power spectrum rise above that of the group-sized haloes. Finally, we present a model for the power suppression due to feedback, which combines observed mean halo baryon fractions with halo mass fractions and halo-matter cross-spectra extracted from dark matter only simulations to predict the power suppression to percent-level accuracy down to $k\,\approx\,10\,h\mathrm{\,Mpc^{-1}}$ without any free parameters.