The surprising accuracy of isothermal Jeans modelling of self-interacting dark matter density profiles

Abstract

Recent claims of observational evidence for self-interacting dark matter (SIDM) have relied on a semi-analytic method for predicting the density profiles of galaxies and galaxy clusters containing SIDM. We present a thorough description of this method, known as isothermal Jeans modelling, and then test it with a large ensemble of haloes taken from cosmological simulations. Our simulations were run with cold and collisionless dark matter (CDM) as well as two different SIDM models, all with dark matter only variants as well as versions including baryons and relevant galaxy formation physics. Using a mix of different box sizes and resolutions, we study haloes with masses ranging from 3 × 1010 to $3 \times 10^{15} \mathrm{\, M_\odot }$. Overall, we find that the isothermal Jeans model provides as accurate a description of simulated SIDM density profiles as the Navarro–Frenk–White profile does of CDM haloes. We can use the model predictions, compared with the simulated density profiles, to determine the input DM–DM scattering cross-sections used to run the simulations. This works especially well for large cross-sections, while with CDM our results tend to favour non-zero (albeit fairly small) cross-sections, driven by a bias against small cross-sections inherent to our adopted method of sampling the model parameter space. The model works across the whole halo mass range we study, although including baryons leads to DM profiles of intermediate-mass ($10^{12} - 10^{13} \mathrm{\, M_\odot }$) haloes that do not depend strongly on the SIDM cross-section. The tightest constraints will therefore come from lower and higher mass haloes: dwarf galaxies and galaxy clusters.

Strong lensing signatures of self-interacting dark matter in low-mass halos

“…This framework, although subject to a few internal inconsistencies (e.g. Sokolenko et al 2018), accurately reproduces the properties of SIDM halos in simulations (Robertson et al 2021). The relative lack of baryons inside dark matter halos on the scales relevant for strong lensing 10 6 − 10 10 M somewhat simplifies the modeling, as we can safely neglect the baryonic mass component of the halos when solving for the density profile.…”

“…The difference in median collapse times between halos in the mass range we consider is much less than the age of the Universe, so accounting for a more precise collapse time would introduce only a weak mass dependence in the model. We note that Robertson et al (2021) used the NFW profile velocity dispersion in place of vrms in Equation 4, while we follow the original paper by Kaplinghat et al (2016) and use vrms. In practice, this choice results in only percent-level differences in the resulting core size.…”

Late-time dark matter oscillations and the core-cusp problem

“…The overall factor of 2 is used to give σT ≈ σ in the isotropic regime, as done in ref. [95]. This new definition of the scattering cross section has been shown to provide better results than σ T in simulations of isolated DM halos [90].…”

The Signatures of Self-Interacting Dark Matter and Subhalo Disruption on Cluster Substructure

“…Several studies have been conducted on the evolution of Milky Way satellites in the presence of SIDM (Fry et al 2015;Robles et al 2017Robles et al , 2019Fitts et al 2018;Sameie et al 2018;Elbert et al 2018;Dooley et al 2016). On cluster mass scales and Robertson et al (2021) have studied the evolution of cluster in the presence of baryons, but have focussed mostly on host profiles. We note that the presence of a massive central galaxy in the cluster can also affect the survivability of satellites that are on highly radial orbits-this effect is more severe in disk centrals due to its axis-symmetric potential.…”