Anisotropic strong lensing as a probe of dark matter self-interactions

Abstract

Galaxy-scale strongly lensed systems have been shown to provide a unique technique for exploring the underlying physics of dark matter at sub-galactic scales. In the past, much attention was given to detecting and studying individual haloes in a strong lens system. In addition to the subhaloes, line-of-sight haloes contribute significantly to the small perturbations in lensed images. In prior work, we demonstrated that these line-of-sight haloes imprint a distinctive anisotropic signature and hence give rise to a detectable non-zero parity-even quadrupole moment in the effective convergence field’s two-point correlation function. In this study, we show that these line-of-sight haloes also produce a non-zero curl component of the effective deflection field with a parity-odd quadrupole moment of the two-point function. These multipole moments have the ability to statistically separate line-of-sight haloes from dark matter substructure. In this paper, we examine how these multipole moments evolve in the presence of warm dark matter and self-interacting dark matter in terms of central density evolution and dark matter halo abundance. Importantly, we show that these different multipole moments display exquisite sensitivity to both the amplitude and the velocity dependence of the dark matter self-interaction cross-section. Our approach opens the door for strong lensing observations to probe dark matter self-interaction over a broad range of relative velocities.

A Self-interacting Dark Matter Solution to the Extreme Diversity of Low-mass Halo Properties

“…In our SIDM scenario, isolated halos are found in both core-expansion and core-collapse phases, yielding an even larger diversity of inner halo profiles than less extreme SIDM models. In parallel, this physics should be detectable in future strong lensing studies using both gravitational imaging and flux-ratio statistics (e.g., see Minor et al 2017;Meneghetti et al 2020Meneghetti et al , 2023Gilman et al 2021Gilman et al , 2023Yang & Yu 2021;Loudas et al 2022;Dhanasingham et al 2023;Zhang et al 2023); observations of MW satellites will also probe our SIDM model, which predicts that a substantial fraction of the low-mass subhalos that host faint dwarf galaxies are core collapsed (e.g., Kaplinghat et al 2019;Correa 2021;Turner et al 2021;Silverman et al 2023;Slone et al 2023;Yang et al 2023a).…”