The first shear measurements from precision weak lensing

TL;DR

This paper introduces a novel end-to-end method to measure weak lensing effects on individual galaxies using their velocity fields, demonstrating its potential to surpass traditional stacking techniques.

Contribution

The study presents the first shear measurements from galaxy velocity fields, offering a new approach to weak lensing analysis that leverages kinematic data of individual systems.

Findings

Measured an average shear of 0.020 ± 0.008

Compared observed shear with predicted values, finding discrepancies

Demonstrated the feasibility of individual galaxy shear measurements

Abstract

We present an end-to-end methodology to measure the effects of weak lensing on individual galaxy-galaxy systems exploiting their kinematic information. Using this methodology, we have measured a shear signal from the velocity fields of 18 weakly-lensed galaxies. We selected a sample of systems based only on the properties of the sources, requiring them to be bright (apparent $i$-band magnitude $ < 17.4$) and in the nearby Universe ($z < 0.15$). We have observed the velocity fields of the sources with WiFeS, an optical IFU on a 2.3m telescope, and fitted them using a simple circular motion model with an external shear. We have measured an average shear of $\langle \gamma \rangle = 0.020 \pm 0.008$ compared to a predicted $\langle \gamma_{pred} \rangle = 0.005$ obtained using median stellar-to-halo relationships from the literature. While still a statistical approach, our results suggest that this new weak lensing methodology can overcome some of the limitations of traditional stacking-based techniques. We describe in detail all the steps of the methodology and make publicly available all the velocity maps for the weakly-lensed sources used in this study.