Substructure Lensing: Effects of Galaxies, Globular Clusters & Satellite Streams

TL;DR

This study investigates the impact of galaxies, globular clusters, and satellite streams on gravitational lensing flux anomalies, finding that these substructures alone cannot fully explain observed anomalies, suggesting possible issues with the CDM model or line-of-sight effects.

Contribution

It extends previous lensing simulations by including baryonic and diffuse dark matter components, assessing their effects on flux-ratio anomalies in gravitational lensing.

Findings

Substructures alone do not account for observed anomalies.

Line-of-sight haloes may contribute to flux anomalies.

Discrepancies could indicate limitations of the CDM model.

Abstract

Lensing flux-ratio anomalies have been frequently observed and taken as evidence for the presence of abundant dark matter substructures in lensing galaxies, as predicted by the cold dark matter (CDM) model of cosmogony. In previous work, we examined the cusp-caustic relations of the multiple images of background quasars lensed by galaxy-scale dark matter haloes, using a suite of high-resolution N-body simulations (the Aquarius simulations). In this work, we extend our previous calculations to incorporate both the baryonic and diffuse dark components in lensing haloes. We include in each lensing simulation: (1) a satellite galaxy population derived from a semi-analytic model applied to the Aquarius haloes, (2) an empirical Milky-Way globular cluster population and (3) satellite streams (diffuse dark component) identified in the simulations. Accounting for these extra components, we confirm our earlier conclusion that the abundance of intrinsic substructures (dark or bright, bound or diffuse) is not sufficient to explain the observed frequency of cusp-caustic violations in the CLASS survey. We conclude that the observed effect could be the result of the small number statistics of CLASS, or intergalactic haloes along the line of sight acting as additional sources of lensing flux anomalies. Another possibility is that this discrepancy signals a failure of the CDM model.