Dark matter millilensing and VSOP-2

TL;DR

This paper assesses the potential for detecting dark matter subhalos through gravitational lensing effects using space VLBI, finding that realistic density profiles make such detection more challenging than previously thought.

Contribution

It provides a detailed analysis of the expected image separations caused by dark matter subhalos with realistic density profiles, challenging earlier optimistic estimates.

Findings

Detection of subhalos is more difficult than previously estimated.

Realistic density profiles predict smaller image separations.

Current and upcoming facilities may struggle to observe these effects.

Abstract

According to the cold dark matter scenario, a large number of dark subhalos should be located within the halo of each Milky-way sized galaxy. One promising possibility for detecting such subhalos is to try to observe their gravitational lensing effects on background sources. Dark matter subhalos in the 10^6 - 10^10 M_solar mass range should cause strong gravitational lensing on the (sub)milliarcsecond scales, which can be observed only using space VLBI. We study the feasibility of a strong-lensing detection of dark subhalos by deriving the image separations expected for density profiles favoured by current simulations and comparing it to the angular resolution of both existing and upcoming observational facilities. We show that the detection of subhalos is likely much more difficult than suggested in previous studies, due to the smaller image separations predicted for subhalo density profiles more realistic than the singular isothermal sphere models often adopted.