Detection of a Companion Lens Galaxy using the Mid-infrared Flux Ratios of the Gravitationally Lensed Quasar H1413+117

TL;DR

This study uses mid-infrared flux ratios of a gravitationally lensed quasar to detect a companion galaxy, demonstrating a new method for identifying galaxy substructures through flux anomalies.

Contribution

First detection of a companion galaxy affecting flux ratios in a gravitational lens using mid-IR observations, confirming the potential of flux anomalies to reveal galaxy substructures.

Findings

Mid-IR flux ratios are unaffected by extinction and microlensing.

A nearby galaxy explains the flux anomaly, indicating substructure presence.

The companion galaxy is detected solely through its flux perturbation effect.

Abstract

We present the first resolved mid-IR (11 micron) observations of the four-image quasar lens H1413+117 using the Michelle camera on Gemini North. All previous observations (optical, near-IR, and radio) of this lens show a "flux anomaly," where the image flux ratios cannot be explained by a simple, central lens galaxy. We attempt to reproduce the mid-IR flux ratios, which are insensitive to extinction and microlensing, by modeling the main lens as a singular isothermal ellipsoid. This model fails to reproduce the flux ratios. However, we can explain the flux ratios simply by adding to the model a nearby galaxy detected in the H-band by HST/NICMOS-NIC2. This perturbing galaxy lies 4.0" from the main lens and it has a critical radius of 0.63" +/- 0.02" which is similar to that of the main lens, as expected from their similar H-band fluxes. More remarkably, this galaxy is not required to obtain a good fit to the system astrometry, so this represents the first clear detection of an object through its effect on the image fluxes of a gravitational lens. This is a parallel to the detections of visible satellites from astrometric anomalies, and provides a proof of the concept of searching for substructure in galaxies using anomalous flux ratios.