Cosmological Simulations of Decaying Dark Matter: Implications for Small-scale Structure of Dark Matter Halos

摘要

We present a set of N-body simulations of a class of models in which anunstable dark matter particle decays into a stable non-interacting dark matterparticle, with decay lifetime comparable to the Hubble time. We study theeffects of the kinematic recoil velocity received by the stable dark matter onthe structures of dark matter halos ranging from galaxy-cluster to Milky Waymass scales. For Milky Way-mass halos, we use high-resolution, zoom-insimulations to explore the effects of decays on Galactic substructure. Ingeneral, halos with circular velocities comparable to the magnitude of kickvelocity are most strongly affected by decays. We show that decaying darkmatter models with lifetimes comparable to Hubble time and recoil speeds about20-40 km/s can significantly reduce both the abundance of Galactic subhalos andthe internal densities of the subhalos. We also compare subhalo circularvelocity profiles with observational constraints on the Milky Way dwarfsatellite galaxies. Interestingly, we find that decaying dark matter modelsthat do not violate current astrophysical constraints, can significantlymitigate both the well-documented "missing satellites problem" and the morerecent "too big to fail problem" associated with the abundances and densitiesof Local Group dwarf satellite galaxies. A relatively unique feature of latedecaying dark matter models is that they predict significant evolution of halosas a function of time. This is an important consideration because at highredshifts, prior to decays, decaying models exhibit the same sequence ofstructure formation as cold dark matter. We conclude that models of decayingdark matter make predictions that are relevant for the interpretation ofobservations of small galaxies in the Local Group and can be tested orconstrained by the kinematics of Local Group dwarf galaxies as well as byforthcoming large-scale surveys.