Globular clusters vs dark matter haloes in strong lensing observations

TL;DR

This paper explores how small distortions in gravitational lensing images can differentiate between dark matter haloes and globular clusters, aiding in understanding dark matter properties and models.

Contribution

It demonstrates that globular clusters can mimic dark matter haloes in lensing signals but can be distinguished through their different mass concentration profiles using high-resolution imaging.

Findings

Globular cluster density is comparable to dark matter perturbers.

Different mass concentrations cause distinguishable lensing distortions.

High-resolution imaging can separate globular cluster signals from dark matter haloes.

Abstract

Small distortions in the images of Einstein rings or giant arcs offer the exciting prospect of detecting dark matter haloes or subhaloes of mass below $10^9$M$_{\odot}$, most of which are too small to have made a visible galaxy. A very large number of such haloes are predicted to exist in the cold dark matter model of cosmogony; in contrast other models, such as warm dark matter, predict no haloes below a mass of this order which depends on the properties of the warm dark matter particle. Attempting to detect these small perturbers could therefore discriminate between different kinds of dark matter particles, and even rule out the cold dark matter model altogether. Globular clusters in the lens galaxy also induce distortions in the image which could, in principle, contaminate the test. Here, we investigate the population of globular clusters in six early type galaxies in the Virgo cluster. We find that the number density of globular clusters of mass $\sim10^6$M$_{\odot}$ is comparable to that of the dark matter perturbers (including subhaloes in the lens and haloes along the line-of-sight). We show that the very different degrees of mass concentration in globular clusters and dark matter haloes result in different lensing distortions. These are detectable with milli-arcsecond resolution imaging which can distinguish between globular cluster and dark matter halo signals.