Constraining velocity-dependent self-interacting dark matter with the Milky Way’s dwarf spheroidal galaxies

Abstract

The observed anti-correlation between the central dark matter (DM) densities of the bright Milky Way (MW) dwarf spheroidal galaxies (dSphs) and their orbital pericenter distances poses a potential signature of self-interacting dark matter (SIDM). In this work we investigate this possibility by analysing the range of SIDM scattering cross section per unit mass, σ/mχ, able to explain such anti-correlation. We simulate the orbital evolution of dSphs subhaloes around the MW assuming an analytical form for the gravitational potential, adopting the proper motions from the Gaia mission and including a consistent characterization of gravitational tidal stripping. The evolution of subhalo density profiles is modelled using the gravothermal fluid formalism, where DM particle collisions induce thermal conduction that depends on σ/mχ. We find that models of dSphs, such as Carina and Fornax, reproduce the observed central DM densities with fixed σ/mχ ranging between 30 and 50 cm2g−1, whereas other dSphs prefer larger values ranging between 70 and 100 cm2g−1. These cross sections correlate with the average collision velocity of DM particles within each subhalo’s core, so that systems modelled with large cross sections have lower collision velocities. We fit the cross section-velocity correlation with a SIDM particle model, where a DM particle of mass mχ = 53.93 ± 9.81 GeV interacts under the exchange of a light mediator of mass mφ = 6.6 ± 0.43 MeV, with the self-interactions being described by a Yukawa potential. The outcome is a cross section-velocity relation that explains the diverse DM profiles of MW dSph satellites and is consistent with observational constraints on larger scales.

N-body simulations of dark matter with frequent self-interactions

“…Another important extension will be to model velocitydependent differential cross-sections, which appear to be preferred by observational data (e.g. Correa 2021;Sagunski et al 2021) and have been investigated in several -body studies (e.g. Colin et al 2002;Vogelsberger et al 2012;Banerjee et al 2020).…”

Testing extensions to ΛCDM on small scales with forthcoming cosmic shear surveys

“…The largest cross-section we examine is somewhat in tension with some of the observations listed here, but it is worth noting that these are primarily focused on large scales (galaxy clusters). There is evidence to suggest that SIDM models with cross-sections as high as 50 cm 2 g −1 are viable when using constraints coming from dwarf galaxies (Elbert et al 2015;Correa 2021). As our focus is on small scales, the range of cross-sections we explore is therefore plausible given current constraints.…”

Unequal-mass mergers of dark matter haloes with rare and frequent self-interactions

“…In future work it would be interesting to also investigate models with a velocity dependence, particularly as such models appear to be in better agreement with astrophysical observations than constant cross-sections (e.g. Kaplinghat et al 2016;Correa 2021;Sagunski et al 2021;Gilman et al 2021).…”