Peter S. Behroozi, Abraham Loeb, Risa H. Wechsler
We study the properties of unbound dark matter particles, defined as having sufficient kinetic energy to escape the boundary of their parent halos. We find that the mass fraction of unbound particles increases strongly towards the edges of halos and in denser environments. Mergers are the largest source of unbound particles; however, major mergers are not especially more efficient than minor mergers in this regard. Because unbound dark matter particles can leave halos more easily than their baryonic counterparts, we also find that standard LCDM cosmology predicts a redshift-dependent boost for the baryon fraction in massive clusters which reaches as high as an extra ~ 20 percent at z=0 compared to the universal value. Our findings have relevance for dark matter detection experiments, precision calibrations of the halo mass function, the use of baryon fractions to constrain dark energy, and searches for intergalactic supernovae.
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http://arxiv.org/abs/1208.0334
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