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 matter (SIDM) on the density profiles and substructure counts of dark matter halos from the scales of spiral galaxies to galaxy clusters, focusing explicitly on models with cross sections over dark matter particle mass σ/m = 1 and 0.1 cm 2 /g. Our simulations rely on a new SIDM N-body algorithm that is derived self-consistently from the Boltzmann equation and that reproduces analytic expectations in controlled numerical experiments. We find that well-resolved SIDM halos have constant-density cores, with significantly lower central densities than their CDM counterparts. In contrast, the subhalo content of SIDM halos is only modestly reduced compared to CDM, with the suppression greatest for large hosts and small halo-centric distances. Moreover, the large-scale clustering and halo circular velocity functions in SIDM are effectively identical to CDM, meaning that all of the large-scale successes of CDM are equally well matched by SIDM. From our largest cross section runs we are able to extract scaling relations for core sizes and central densities over a range of halo sizes and find a strong correlation between the core radius of an SIDM halo and the NFW scale radius of its CDM counterpart. We construct a simple analytic model, based on CDM scaling relations, that captures all aspects of the scaling relations for SIDM halos. Our results show that halo core densities in σ/m = 1 cm 2 /g models are too low to match observations of galaxy clusters, low surface brightness spirals (LSBs), and dwarf spheroidal galaxies. However, SIDM with σ/m ≃ 0.1 cm 2 /g appears capable of reproducing reported core sizes and central densities of dwarfs, LSBs, and galaxy clusters without the need for velocity dependence. Higher resolution simulations over a wider range of masses will be required to confirm this expectation. We discuss constraints arising from the Bullet cluster observations, measurements of dark matter density on small-scales and subhalo survival requirements, and show that SIDM models with σ/m ≃ 0.1 cm 2 /g ≃ 0.2 barn/GeV are consistent with all observational constraints.

Tidal features of classical Milky Way satellites in a Λ cold dark matter universe

“…5. These systems have less dramatic differences between peak mass and current mass and their infall times are typically more recent (∼ 4-9 Gyr ago), consistent with previous studies of the likely infall times of different MW dSphs (Rocha et al 2013). Their gas content and SFR fall to zero more quickly after infall, around the first apocentre unless their orbit stays far from the galactic centre the whole time (e.g.…”

The variation of rotation curve shapes as a signature of the effects of baryons on dark matter density profiles

“…Indeed, Rocha et al (2013) find scatter in core sizes at given halo mass. Future studies will be able to quantify such scatter, and its mass dependence, which may result in a better match between the SIDM model and observations for smaller core sizes.…”

Hubble Frontier Field free-form mass mapping of the massive multiple-merging cluster MACSJ0717.5+3745

“…2014c) is the possibility that dark matter has a small, but not negligible, probability of interaction. Simulations have shown that this mechanism, if present, is able to flatten the cusps of cluster halos and on the necessary scales up to 100 kpc (Rocha et al 2013). In addition to the flattening, if DM interacts, it should exhibit a friction effect that could in principle be studied by possible shifts between the peaks of the DM distribution and the galaxies.…”