Speaker
Description
The Cold Dark Matter (CDM) paradigm remains the most successful framework for describing the formation and evolution of cosmic structure, yet its predictions on sub-galactic scales are still only weakly tested. A key prediction of CDM is the existence of a large population of low-mass dark matter haloes with a well-defined mass density profile, both as subhaloes within galaxies and as isolated structures along the line of sight.
Since the majority of these objects are expected to be completely dark, strong gravitational lensing provides a unique opportunity to study them and to probe the nature of dark matter.
In this talk, I will review the current status of the field and present the latest observational constraints from strong-lensing studies. Recent advances have pushed strong lensing into a previously inaccessible regime of halo mass and physical scale. In particular, Powell et al. (2025) reported the detection of a dark perturber with an enclosed mass of only $10^6$M$_{sun}$ identified through its effect on an exceptionally thin lensed arc observed with milli-arcsecond-resolution VLBI. This represents the lowest-mass object detected at cosmological distance through its gravitational influence and demonstrates, for the first time, that strong lensing can directly probe the million-solar-mass regime beyond the Local Group.
I will also present the latest constraints on the internal structure of the three currently known low-mass detections and show how their inferred properties compare with predictions from different dark matter models. I will then focus on the expected role of existing and upcoming observing facilities such as Euclid, ELTs, SKA, and the ngVLA in this field.