Shape noise and dispersion in precision weak lensing

TL;DR

This paper introduces a new precision weak lensing method using velocity data to measure galaxy shear, revealing low shape noise and significant astrophysical dispersion, advancing the accuracy of galaxy mass measurements.

Contribution

It models the shear distribution considering shape noise and astrophysical dispersion, demonstrating PWL's higher precision over traditional weak lensing.

Findings

Effective shape noise of 0.024 ± 0.007, much lower than conventional methods.

Measured shear dispersion of 0.53 dex, indicating high halo mass variability.

PWL is approximately 10 times more precise than traditional weak lensing.

Abstract

We analyse the first measurements from precision weak lensing (PWL): a new methodology for measuring individual galaxy-galaxy weak lensing through velocity information. Our goal is to understand the observed shear distribution from PWL, which is broader than can be explained by the statistical measurement errors. We identify two possible sources of scatter to explain the observed distribution: a shape noise term associated with the underlying assumption of circular stable rotation, and an astrophysical signal consistent with a log-normal dispersion around the stellar-to-halo mass relation (SHMR). We have modelled the observed distribution as the combination of these two factors and quantified their most likely values given our data. For the current sample, we measure an effective shape noise of $\sigma_\gamma = 0.024 \pm 0.007$, highlighting the low noise impact of the method and positioning PWL as $\sim 10$ times more precise than conventional weak lensing. We also measure an average dispersion in shears of $\xi_\gamma = 0.53^{+0.26}_{-0.28}$\,dex over the range of $8.5 < \log M_\star < 11$. This measurement is higher than expected, which is suggestive of a relatively high dispersion in halo mass and/or profile.