Strong lensing by subhalos in the dwarf-galaxy mass range I: Image separations

TL;DR

This paper investigates the potential for detecting dark matter subhalos in dwarf-galaxy-sized halos via gravitational lensing image separations, finding that current technology may only detect the most optimistic models due to very small predicted separations.

Contribution

It provides updated estimates of lensing image separations caused by subhalos based on recent N-body simulation profiles, challenging previous assumptions of detectability.

Findings

Image separations are highly sensitive to subhalo density profiles.

Most models predict separations smaller than current detection capabilities.

Detection of dark subhalos via lensing will be more challenging than previously thought.

Abstract

The cold dark matter scenario predicts that a large number of dark subhalos should be located within the halo of each Milky-way sized galaxy. One tell-tale signature of such dark subhalos could be additional milliarcsecond-scale image splitting of quasars previously known to be multiply-imaged on arcsecond scales. Here, we estimate the image separations for the subhalo density profiles favoured by recent N-body simulations, and compare these to the angular resolution of both existing and upcoming observational facilities. We find, that the image separations produced are very sensitive to the exact subhalo density profile assumed, but in all cases considerably smaller than previous estimates based on the premise that subhalos can be approximated by singular isothermal spheres. Only the most optimistic subhalo models produce image separations that would be detectable with current technology, and many models produce image separations that will remain unresolved with all telescopes expected to become available in the foreseeable future. Detections of dark subhalos through image-splitting effects will therefore be far more challenging than currently believed, albeit not necessarily impossible.