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

TL;DR

DARKSKIES presents a 100-object, high-resolution, zoom-in simulation suite of massive galaxy clusters in a self-interacting dark matter framework, spanning cross-sections $0$, $0.01$, $0.05$, $0.1$, and $0.2$ cm$^2$/g and calibrated to reproduce realistic baryonic properties. Implemented via the TANGO-SIDM scheme within the SWIFT-EAGLE framework, it leverages super-sampled initial conditions from MUSIC to resolve core-scale scatterings while preserving computational efficiency. The study finds that SIDM generates cores in density profiles primarily at $z<0.5$, and reveals a pronounced BCG wobble in SIDM that correlates with mass accretion and exhibits an anti-correlation between BCG velocity and offset, consistent with a harmonic oscillator in a cored potential; the wobble lag is $t_{ m lag}\approx2.6\pm0.6$ Gyr, and the strongest signal occurs at higher cross-sections ($\sigma_{ m DM}/m=0.2$ cm$^2$/g). The ensemble provides predictions and a publicly accessible dataset to enable robust SIDM constraints for upcoming surveys (e.g., Euclid), targeting $\sigma_{ m DM}/m<0.1$ cm$^2$/g and capturing observable signatures in cluster cores.

Abstract

We present the "DARKSKIES" suite of one hundred, zoom-in hydrodynamic simulations of massive ($M_{200}>5\times10^{14}{\rm M}_\odot)$ galaxy clusters with self-interacting dark matter (SIDM). We super-sample the simulations such that $m_{\rm DM}/m_{\rm gas}\sim0.1$, enabling us to simulate a dark matter particle mass of $m=0.68\times10^{8}M_\odot$ an order of magnitude faster, whilst exploring SIDM in the core of clusters at extremely high resolution. We calibrate the baryonic feedback to produce observationally consistent and realistic galaxy clusters across all simulations and simulate five models of velocity-independent SIDM targeting the expected sensitivity of future telescopes - $σ_{\rm DM}/m=0.,0.01,0.05,0.1,0.2$ cm$^2$/g. We find 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 investigate the dynamics of the brightest cluster galaxy inside the dark matter halo and find in SIDM cosmologies there exists a so-called wobbling not observed in collisionless dark matter. We find this wobble is driven by accreting mass on to 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.

Figures (14)

• Figure 1: The validation check of our super-sampled initial conditions. By stitching multiple runs of MUSIC we create non-standard combinations of dark matter and gas mass zoom-in simulations. We run five zoom-in simulations using the same initial conditions, increasing the dark matter mass resolution. We simulate each to a redshift of $z=1$ and show the total matter density profile here in the left hand panel with the relevant convergence radii in the grey regions (c.f. \ref{['eqn:convergence_rad']}). We find consistent density profiles over the range of mass resolutions. The right hand panel shows the corresponding wall-clock time to simulate each halo to the same redshift. The colour and line-style match those in the left hand panel, we also show the final wall-clock time to simulate to $z=1$ in the legend.
• Figure 2: The distribution of total mass ($M_{200}$), of the 100 most massive galaxy clusters selected from the initial $400$ Mpc$/h$ box to be re-simulated.
• Figure 3: Final calibrated set of DARKSKIES CDM clusters. In each panel we show the zoom-in, super-sampled clusters with CDM in black stars. Specifically, top left: the gas fraction inside $r_{500}$ as a function of the halo mass $M_{500}$, top right: the stellar fraction inside $r_{500}$ as a function of the halo mass $M_{500}$, bottom left: the projected half mass radius of the central galaxy (considering all stars inside $100$kpc) as a function of projected stellar mass within $100$kpc, bottom right: The projected stellar mass within $100$kpc as a function of halo mass. The Flamingo HST Data corresponds to a collection of gas mass estimates collated by the Flamingo team gas_fractiongas_fraction_agas_fraction_bgas_fraction_cgas_fraction_dgas_fraction_egas_fraction_f. The solid line in each case shows the best fit and the regions show the 68% and 95% around this fit.
• Figure 4: The total mass density map for the halo 20926 at different redshifts (columns), simulated in different dark matter models (rows). Each panel has a field-of-view of $1\times1$ pMpc and has the same scaled colour bar and has been projected along the z-axis of the simulation box.
• Figure 5: The total (top panel), dark matter (bottom left panel), stellar (bottom middle panel) and gas (bottom right panel) mass density profiles as a function of self-interaction cross-section. In each case we show, $\Delta\rho$ - the density relative to CDM and in the main panel we show the BAHAMAS SIDM simulations as dashed lines. In each case the shaded region shows the 16% and 84% of the simulations.