Cosmological simulations with self-interacting dark matter – I. Constant-density cores and substructure

Abstract

We use cosmological simulations to study the effects of self-interacting dark\nmatter (SIDM) on the density profiles and substructure counts of dark matter\nhalos from the scales of spiral galaxies to galaxy clusters, focusing\nexplicitly on models with cross sections over dark matter particle mass\n\\sigma/m = 1 and 0.1 cm^2/g. Our simulations rely on a new SIDM N-body\nalgorithm that is derived self-consistently from the Boltzmann equation and\nthat reproduces analytic expectations in controlled numerical experiments. We\nfind that well-resolved SIDM halos have constant-density cores, with\nsignificantly lower central densities than their CDM counterparts. In contrast,\nthe subhalo content of SIDM halos is only modestly reduced compared to CDM,\nwith the suppression greatest for large hosts and small halo-centric distances.\nMoreover, the large-scale clustering and halo circular velocity functions in\nSIDM are effectively identical to CDM, meaning that all of the large-scale\nsuccesses of CDM are equally well matched by SIDM. From our largest cross\nsection runs we are able to extract scaling relations for core sizes and\ncentral densities over a range of halo sizes and find a strong correlation\nbetween the core radius of an SIDM halo and the NFW scale radius of its CDM\ncounterpart. We construct a simple analytic model, based on CDM scaling\nrelations, that captures all aspects of the scaling relations for SIDM halos.\nOur results show that halo core densities in \\sigma/m = 1 cm^2/g models are too\nlow to match observations of galaxy clusters, low surface brightness spirals\n(LSBs), and dwarf spheroidal galaxies. However, SIDM with \\sigma/m ~ 0.1 cm^2/g\nappears capable of reproducing reported core sizes and central densities of\ndwarfs, LSBs, and galaxy clusters without the need for velocity dependence.\n(abridged)\n