TNGC-SIDM I: Evolution of massive cluster mergers under the self-interacting dark matter paradigm

Abstract

Merging galaxy clusters provide an ideal laboratory for testing the self-interacting nature of dark matter. In this paper, we present a pilot study of magnetohydrodynamical cosmological zoom-in simulations of two cluster mergers selected from TNG-Cluster, with $M_{200c}\sim 9\times 10^{14}{M}_{\odot }$ and $M_{200c}\sim 2\times 10^{14}{M}_{\odot }$. The simulations are performed with both standard collisionless cold dark matter (CDM) and self-interacting dark matter (SIDM), assuming an isotropic, velocity-independent cross-section of ${\sigma }_{\mathrm{T}}/m_{\chi }=1\mathrm{c}{\mathrm{m}}^2{\mathrm{g}}^{-1}$, with an additional $0.5\mathrm{c}{\mathrm{m}}^2{\mathrm{g}}^{-1}$ run for the low-mass system, and the mass resolution and galaxy formation model are unchanged from TNG-Cluster. We show how dark matter self-interactions produce an isothermal core in the dark matter halo, generate unique substructures in the intracluster light, and introduce variation in the multi-wavelength observables of the intracluster plasma. Using these simulations, we test the validity of observational probes for dark matter self-interactions in cluster mergers. We find that the shock-to-shock separation shows similar evolution in the self-interaction models tested here, providing a reference for distinguishing the $\sim 100-200\mathrm{kpc}$-scale difference in halo separation induced by self-interactions. Moreover, the dark matter halo centroid of the main cluster in the massive cluster merger is offset from the brightest cluster galaxy by as much as $\sim 20\mathrm{kpc}$, larger than the offset in the sub-cluster. This offset persists beyond 4 Gyr after the first pericenter passage. Our results indicate that sample selection plays a key role in testing the possible self-interacting nature of dark matter using cluster mergers, and that double radio relic cluster mergers and massive clusters with evidence of an ancient major merger offer a promising testbed for this purpose.

24 pages, 23 figures. To be submitted to A&A. Comments welcome