Flashlights: Properties of Highly Magnified Images Near Cluster Critical Curves in the Presence of Dark Matter Subhalos

TL;DR

This paper investigates how dark matter subhalos near galaxy cluster critical curves affect highly magnified images, revealing distinctive asymmetries and observable flux variations that differ from stellar microlensing.

Contribution

It provides a detailed analysis of the lensing effects of dark matter subhalos with extended profiles, highlighting their unique signatures compared to microlensing by stars.

Findings

Subhalos cause pixel flux variations >0.1 magnitudes on the positive parity side.

Asymmetry in image properties is more pronounced than in stellar microlensing.

Signatures of subhalo lensing can be observed up to 1 arcsecond from cluster critical curves.

Abstract

Dark matter subhalos with extended profiles and density cores, and globular stars clusters of mass $10^6-10^8 M_\odot$, that live near the critical curves in galaxy cluster lenses can potentially be detected through their lensing magnification of stars in background galaxies. In this work we study the effect such subhalos have on lensed images, and compare to the case of more well studied microlensing by stars and black holes near critical curves. We find that the cluster density gradient and the extended mass distribution of subhalos are important in determining image properties. Both lead to an asymmetry between the image properties on the positive and negative parity sides of the cluster that is more pronounced than in the case of microlensing. For example, on the negative parity side, subhalos with cores larger than about $50\,$pc do not generate any images with magnification above $\sim 100$ outside of the immediate vicinity of the cluster critical curve. We discuss these factors using analytical and numerical analysis, and exploit them to identify observable signatures of subhalos: subhalos create pixel-to-pixel flux variations of $\gtrsim 0.1$ magnitudes, on the positive parity side of clusters. These pixels tend to cluster around (otherwise invisible) subhalos. Unlike in the case of microlensing, signatures of subhalo lensing can be found up to $1''$ away from the critical curves of massive clusters.