Meso‐Structure in Three Strong‐lensing Systems

We map substructure in three strong lensing systems having particularly goodimage data: the galaxy lens MG J0414+053 and the clusters SDSS J1004+411 andACO 1689. Our method is to first reconstruct the lens as a pixelated mass mapand then substract off the symmetric part (in the galaxy case) or a projectedNFW (for the cluster lenses). In all three systems we find extended irregularstructures, or meso-structures, having of order 10% of the total mass. InJ0414+053, the meso-structure suggests a tidal tail connecting the main lenswith a nearby galaxy; however this interpretation is tentative. In the clustersthe identification of meso-structure is more secure, especially in ACO 1689where two independent sets of lensed images imply very similar meso-structure.In all three cases the meso-structures are correlated with galaxies but muchmore extended and massive than the stellar components of single galaxies. Suchextended structures cannot plausibly persist in such high-density regionswithout being mixed; the crossing times are too short. The meso-structurestherefore appear to be merging or otherwise dynamically evolving systems.Comment: To appear in Ap