Astrometric Signatures of Dark Matter Subhalos in Galaxy Clusters

Strong gravitational lensing in galaxy clusters offers a unique method to probe dark matter structures at small scales. This ongoing study focuses on the astrometric shifts in highly magnified, symmetric image pairs of background stars caused by subhalos near the critical curve of a galaxy cluster. In a smooth lensing model, these image pairs align symmetrically with respect to a flat critical curve, but the presence of subhalos induces detectable shifts, disrupting it into a "wiggling" pattern. By comparing observed deviations with theoretical models, we infer subhalo properties, with early results showing sensitivity to subhalos in the mass range of one to hundreds of millions of solar masses. These astrometric signatures, detectable by instruments like the James Webb Space Telescope, provide a powerful tool for understanding the nature of dark matter and the role that substructure plays in late-Universe cosmology.