http://arxiv.org/abs/1402.1493
Based on a set of large–scale cosmological simulations, we investigate baryon effects on the halo mass function, with emphasis on the role played by AGN feedback. Halo mass functions are computed after identifying halos with both Friends-of-Friends and Spherical Overdensity halo finding algorithms. We embed the standard SO algorithm into a memory-controlled frame program and present the $\rm P$python spher$\rm I$c$\rm A$l $\rm O$verdensity code — PIAO. The SO halos are identified at three overdensities $\Delta_c = 2500, 500, 200$, and masses computed within the three corresponding radii. We confirm that hydrodynamical simulations based on radiative cooling, star formation and supernova feedback (CSF) produce mass functions higher than from collisionless simulations. In contrast, the effect of AGN feedback is that to suppressing the HMFs to a level even below that of Dark Matter simulations, for both FoF and SO halos. We find that the ratio between the halo mass functions in the AGN and in the DM simulations is ~ 0.8, almost independent of the mass, when estimated at overdensity $\Delta_c=500$, a difference that increases at higher overdensity $\Delta_c=2500$, with no significant redshift dependence for these ratios. We verify that the decrease of the HMF in the AGN simulation is induced by a corresponding decrease of halo masses with respect to the DM case. The shallower inner density profiles of halos in the AGN simulation witnesses that mass reduction is induced by the sudden expulsion of displacement of gas induced by AGN energy feedback. We provide fitting functions to describe halo mass variations at different overdensities. We demonstrate that, using these fitting functions, we recover the DM halo mass function starting from that of hydrodynamical simulations, with a residual random scatter $\leqslant 5$ per cent for halo mass larger than $10^{13} h^{-1} M_{\odot}$.
W. Cui, S. Borgani and G. Murante
Mon, 10 Feb 14
24/49
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