A shot in the dark: searching for dark substructures in the RX J0437+00 galaxy cluster

TL;DR

This paper explores the use of hyperbolic-umbilic lensing in the galaxy cluster RX J0437+00 to tentatively detect a low-mass dark matter subhalo, advancing methods for studying dark matter substructures.

Contribution

It introduces a novel approach using HU lensing configurations to search for dark matter subhalos in galaxy clusters, providing initial evidence and outlining future research directions.

Findings

Tentative detection of a dark matter subhalo (~2.25 billion solar masses)

Demonstrates HU lensing as a promising tool for dark matter substructure studies

Highlights need for deeper data and advanced modelling for confirmation

Abstract

Obtaining a census of dark matter structures at low mass ($\leq 10^9 M_\odot$) can provide strong constraints on the nature of dark matter, though identifying such structures remains difficult. In this work, we study the galaxy cluster RX J0437.1+0043, taking advantage of its powerful "exotic" Hyperbolic-Umbilic (HU) lensing configuration to search for substructure candidates. Using a combination of high resolution imaging, IFU spectroscopy, and gravitational lensing modelling, we report on a tentative detection of a dark matter subhalo ($m_{\rm halo} = 2.25 \pm 0.94 \times 10^9 M_\odot$) near the vicinity of one of the largest HU images. We stress that this result is still preliminary and that deeper data and more advanced modelling techniques are needed to ultimately confirm this detection. Nevertheless, this work outlines the first steps towards understanding subhalo properties in dense cluster environments, developing HU cluster lenses as a potential new tool for investigating dark matter.