Probing dark matter structure down to $10^7$ solar masses: flux ratio statistics in gravitational lenses with line of sight halos

Understand

Strong lensing provides a powerful means of investigating the nature of dark matter as it probes dark matter structure on sub-galactic scales.

• We present an extension of a forward modeling framework that uses flux ratios from quadruply imaged quasars (quads) to measure the shape and amplitude of the halo mass function, including line of sight (LOS) halos and main deflector subhalos.
• We apply this machinery to 50 mock lenses --- roughly the number of known quads --- with warm dark matter (WDM) mass functions exhibiting free-streaming cutoffs parameterized by the half-mode mass $m_{\rm{hm}}$.
• Assuming cold dark matter (CDM), we forecast bounds on $m_{\rm{hm}}$ and the corresponding thermal relic particle masses over a range of tidal destruction severity, assuming a particular WDM mass function and mass-concentration relation.