Offset between dark matter and ordinary matter: evidence from a sample of 38 lensing clusters of galaxies

TL;DR

This study analyzes 38 galaxy clusters to measure the spatial offsets between dark matter and baryonic matter, revealing significant separations that impact lensing models and cosmological theories.

Contribution

It provides the first systematic measurement of offsets between dark matter and baryonic matter in a sizable sample of galaxy clusters, highlighting their prevalence in unrelaxed systems.

Findings

45% of clusters have offsets >10"

Offsets are significant given measurement precision

Offsets suggest spatial separation in unrelaxed clusters

Abstract

We compile a sample of 38 galaxy clusters which have both X-ray and strong lensing observations, and study for each cluster the projected offset between the dominant component of baryonic matter center (measured by X-rays) and the gravitational center (measured by strong lensing). Among the total sample, 45% clusters have offsets >10". The >10" separations are significant, considering the arcsecond precision in the measurement of the lensing/X-ray centers. This suggests that it might be a common phenomenon in unrelaxed galaxy clusters that gravitational field is separated spatially from the dominant component of baryonic matter. It also has consequences for lensing models of unrelaxed clusters since the gas mass distribution may differ from the dark matter distribution and give perturbations to the modeling. Such offsets can be used as a statistical tool for comparison with the results of Lambda-CDM simulations and to test the modified dynamics.