DARKSKIES: A suite of super-sampled zoom-in simulations of galaxy clusters with self-interacting dark matter

¹ Laboratoire d’Astrophysique, EPFL, Observatoire de Sauverny, 1290 Versoix, Switzerland
² Lorentz Institute for Theoretical Physics, Leiden University, PO Box 9506 NL-2300 RA, Leiden, The Netherlands
³ Leiden Observatory, Leiden University, PO Box 9513 NL-2300 RA, Leiden, The Netherlands
⁴ Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland

^⋆ Corresponding author: david.harvey@epfl.ch

Received: 16 April 2025
Accepted: 28 August 2025

Abstract

We present the ‘DARKSKIES’ suite of one hundred, zoom-in hydrodynamic simulations of massive (M₂₀₀ > 5 × 10¹⁴ M_⊙) galaxy clusters with self-interacting dark matter (SIDM). We super-sampled the simulations such that m_DM/m_gas ∼ 0.1, enabling us to simulate a dark matter particle mass of m = 0.68 × 10⁸ M_⊙ an order of magnitude faster, whilst exploring SIDM in the core of clusters at extremely high resolution. We calibrated the baryonic feedback to produce observationally consistent and realistic galaxy clusters across all simulations and simulated five models of velocity-independent SIDM targeting the expected sensitivity of future telescopes - σ_DM/m = 0.,0.01, 0.05, 0.1, 0.2 cm²/g. We find that the density profiles exhibit the characteristic core even in the smallest of cross-sections, with cores developing only at late times (z < 0.5). We investigated the dynamics of the brightest cluster galaxy (BCG) inside the dark matter halo and find that in SIDM cosmologies there exists a so-called wobbling not observed in collisionless dark matter. We find that this wobble is driven by mass accreting onto a cored density profile with the signal peaking at z = 0.25 and dropping thereafter. This finding is further supported by the existence of an anti-correlation between the offset between the BCG and the dark matter halo and its relative velocity in SIDM only, a hallmark of harmonic oscillation.