Abstract:
The Cold Dark Matter (CDM) model describes dark matter as a non-relativistic (cold) and collisionless particle, predicting a vast population of dark matter haloes across a wide range of masses, from galaxy clusters to Earth-mass haloes. This model has successfully explained many cosmic structures. Yet, decades of searches in laboratories have failed to detect CDM particles directly, spurring interest in alternatives like Warm Dark Matter (WDM). Unlike CDM, WDM suggests that dark matter particles are relativistic, which would inhibit the formation of small dark matter haloes (10^7 - 10^10 M☉). Verifying the abundance of these sub-galactic haloes is critical for determining whether dark matter is indeed “cold”. However, detecting these dark haloes is challenging, as they do not host visible galaxies. Gravitational lensing offers a unique means of studying these "dark" structures. When a galaxy lies behind another, the foreground galaxy’s gravity distorts the background light, with smaller dark matter haloes causing subtle additional perturbations. Analyzing these distortions allows us to indirectly measure the mass and distribution of those invisible haloes. In this talk, I will provide an overview of the methodologies, findings, and ongoing challenges in detecting these haloes through galaxy strong lensing. I will highlight our progress, achieved through a long-term collaboration between Durham and NAOC, in enhancing techniques to identify subtle perturbations from dark subhaloes, which also significantly improves galaxy-galaxy lensing models in general.
