Non-Halo Structures and their Effects on Gravitational Lensing

Understand

Anomalies in the flux-ratios of the images of quadruply-lensed quasars have been used to constrain the nature of dark matter.

• Assuming these lensing perturbations are caused by dark matter haloes, it is currently possible to constrain the mass of a hypothetical Warm Dark Matter (WDM) particle to be $m_\chi > 5.2$ keV.
• However, the assumption that perturbations are only caused by DM haloes might not be correct as other structures, such as filaments and pancakes, exist and make up a significant fraction of the mass in the universe, ranging between 5$\%$ -- 50$\%$ depending on the dark matter model.
• Using novel fragmentation-free simulations of 1 and 3keV WDM cosmologies we study these "non-halo" structures and estimate their impact on flux-ratio observations.