Intracluster light as a dark matter tracer: how their spatial and kinematic relationship is shaped by satellite demographics

TL;DR

This study uses N-body simulations to show that the spatial and kinematic differences between intracluster light and dark matter are primarily driven by satellite galaxy demographics, enabling ICL to trace underlying dark matter distributions.

Contribution

It introduces a predictive model linking satellite demographics to the phase-space and radial distribution differences between ICL and dark matter in galaxy clusters.

Findings

Stripped stars occupy lower-energy, lower-angular momentum regions than stripped dark matter.

The phase-space difference increases with the satellite-to-host mass ratio.

The ICL is always more centrally concentrated than dark matter, with offset magnitude depending on satellite mass.

Abstract

We investigate how the orbital evolution and mass distribution of infalling satellite galaxies shape the phase-space and radial distributions of intracluster light (ICL) relative to the underlying cluster dark matter (DM) halo. Using N-body simulations, we follow the tidal stripping and orbital evolution of satellite galaxies as they are accreted into a live cluster halo, systematically varying satellite-to-host mass ratio and orbital circularity. We measure the specific orbital energy and angular momentum of stripped stellar and DM material, finding that the stripped stars consistently occupy lower-energy and lower-angular momentum regions of phase-space than the stripped DM. The magnitude of this difference increases strongly towards more equal satellite--to--host mass ratios, while the dependence on orbital circularity is weak. We construct a predictive model for the phase-space properties of stripped stars and DM from a whole infalling satellite population and find that the resulting phase-space difference between the components are driven primarily by the characteristic mass of the infalling satellite stellar mass function. We find that the ICL is always more centrally concentrated than the DM. The magnitude of this offset depends on the characteristic mass and increases towards higher characteristic masses. Comparisons with four independent cosmological hydrodynamical simulations show that, once the infalling satellite stellar mass function is matched, the model reproduces the radial stellar-to-DM density profile offsets to better than the inter-simulation scatter. This demonstrates that the radial relationship between the ICL and the DM distribution is largely governed by satellite demographics. With adequate constraints on the infalling satellite population, ICL density profiles can therefore be used as informative tracers of the underlying radial DM distribution in clusters.