Detection of Substructure in the Gravitationally Lensed Quasar MG0414+0534 using Mid-Infrared and Radio VLBI Observations

TL;DR

This study detects substructure in a gravitational lens system MG0414+0534 using mid-infrared and VLBI observations, revealing flux ratio anomalies indicative of satellite dark matter subhalos.

Contribution

It combines mid-IR and VLBI data to identify and characterize a satellite substructure causing flux anomalies in a gravitational lens system.

Findings

Flux ratio anomaly detected between images A1 and A2.

A satellite substructure with mass between 10^6.2 and 10^7.5 solar masses identified.

Mid-IR and VLBI data combined to model substructure effects.

Abstract

We present 11.2 micron observations of the gravitationally lensed, radio-loud z_s=2.64 quasar MG0414+0534, obtained using the Michelle camera on Gemini North. We find a flux ratio anomaly of A2/A1= 0.93 +/- 0.02 for the quasar images A1 and A2. When combined with the 11.7 micron measurements from Minezaki et al. (2009), the A2/A1 flux ratio is nearly 5-sigma from the expected ratio for a model based on the two visible lens galaxies. The mid-IR flux ratio anomaly can be explained by a satellite (substructure), 0.3" Northeast of image A2, as can the detailed VLBI structures of the jet produced by the quasar. When we combine the mid-IR flux ratios with high-resolution VLBI measurements, we find a best-fit mass between 10^(6.2) and 10^(7.5) M_sol inside the Einstein radius for a satellite substructure modeled as a singular isothermal sphere at the redshift of the main lens (z_l=0.96). We are unable to set an interesting limit on the mass to light ratio due to its proximity to the quasar image A2. While the observations used here were technically difficult, surveys of flux anomalies in gravitational lenses with the James Webb Space Telescope will be simple, fast, and should well constrain the abundance of substructure in dark matter haloes.