Confronting ΛCDM with Gravitational Lensing Constraints on Small Scale Structure

This paper primarily addresses the question of whether recent lensing observations probing the small scale structure in the universe are consistent with the ΛCDM model. Here a conservative approach is taken where only the most difficult to explain cases of image flux anomalies in strong lenses are considered. Numerical simulations are performed to compare predictions for the ΛCDM small scale mass function with observed flux ratios. It is found that all the cusp caustic lens anomalies and the disagreements between monochromatic flux ratios and simple lens models can be explained without any substructure in the primary lenses’ dark matter halos. Extragalactic ΛCDM halos are enough to naturally explain these cases. However, spectroscopic gravitational lensing observations of Q2237+0305 – and, less conclusively, bent lensed radio jets – require more small mass halos (∼ 10 M⊙) than is expected in the ΛCDM model.