Observable tests of self-interacting dark matter in galaxy clusters: cosmological simulations with SIDM and baryons

Abstract

We present BAHAMAS-SIDM, the first large-volume, (400 h −1 Mpc) 3 , cosmological simulations including both self-interacting dark matter (SIDM) and baryonic physics. These simulations are important for two primary reasons: 1) they include the effects of baryons on the dark matter distribution 2) the baryon particles can be used to make mock observables that can be compared directly with observations. As is well known, SIDM haloes are systematically less dense in their centres, and rounder, than CDM haloes. Here we find that that these changes are not reflected in the distribution of gas or stars within galaxy clusters, or in their X-ray luminosities. However, gravitational lensing observables can discriminate between DM models, and we present a menu of tests that future surveys could use to measure the SIDM interaction strength. We ray-trace our simulated galaxy clusters to produce strong lensing maps. Including baryons boosts the lensing strength of clusters that produce no critical curves in SIDM-only simulations. Comparing the Einstein radii of our simulated clusters with those observed in the CLASH survey, we find that σ/m < 1 cm 2 g −1 at velocities around 1000 km s −1 .

What does strong gravitational lensing? The mass and redshift distribution of high-magnification lenses

“…Our procedure for generating lensing maps from simulated haloes follows Robertson et al (2019), who studied the Einstein radii of galaxy clusters from bahamas simulations run with different DM models. For each halo at each snapshot redshift, we first find all mass within 5 r200 of the particle with the lowest gravitational potential energy.…”

“…As both κ, and the gravitational shear, γ, are second derivatives of the projected Newtonian potential, they can be readily calculated from one another using discrete Fourier transforms (see e.g. Robertson et al 2019). We can then make a map of the magnification µ using…”

“…those from bahamas, ∂τ /∂ log M is similar between the hydrodynamical simulations and H08. Robertson et al (2019) looked at the density profiles of bahamas clusters, both DM-only and including baryons, and found that the total density at the centre of clusters increases when simulations include baryons, not just because of the contribution from stars (which should be captured by H08 who included analytical potentials associated with a stellar disc and bulge), but also because the DM profile itself becomes more centrally concentrated due to adiabatic contraction (Gnedin et al 2004). The fact that this does not push the bahamas curve above that from H08 probably reflects the fact that in H08 the analytical baryonic potential is added to the DM distribution from a DM-only simulation.…”

The distribution of dark matter and gas spanning 6 Mpc around the post-merger galaxy cluster MS 0451−03

“…Evans & Bridle 2009;Oguri et al 2010;Clampitt & Jain 2016;van Uitert et al 2017;Chiu et al 2018;Shin et al 2018;Umetsu et al 2018). The latter is of particular interest since it reflects the nature of dark matter (specifically whether dark matter is collisionless; Robertson et al 2019). On larger scales, the mass distribution's shape is governed by accretion of matter from the surroundings.…”

Connecting the structure of dark matter haloes to the primordial power spectrum

“…This can be done through direct changes to the equations of motion, such as self-interacting dark matter (e.g. Vogelsberger et al 2014b;Robertson et al 2019), or changes to the linear power spectra in the early universe, such as warm dark matter (e.g. Lovell et al 2017;Hellwing et al 2016) and a running of the spectral index (e.g.…”