# Practical Weak-lensing Shear Measurement with Metacalibration

## Abstract

Metacalibration is a recently introduced method to accurately measure weak gravitational lensing shear using only the available imaging data, without need for prior information about galaxy properties or calibration from simulations. The method involves distorting the image with a small known shear, and calculating the response of a shear estimator to that applied shear. The method was shown to be accurate in moderate-sized simulations with galaxy images that had relatively high signal-to-noise ratios, and without significant selection effects. In this work we introduce a formalism to correct for both shear response and selection biases. We also observe that for images with relatively low signal-to-noise ratios, the correlated noise that arises during the metacalibration process results in significant bias, for which we develop a simple empirical correction. To test this formalism, we created large image simulations based on both parametric models and real galaxy images, including tests with realistic point-spread functions. We varied the point-spread function ellipticity at the five-percent level. In each simulation we applied a small few-percent shear to the galaxy images. We introduced additional challenges that arise in real data, such as detection thresholds, stellar contamination, and missing data. We applied cuts on the measured galaxy properties tomore »

- Authors:

- Brookhaven National Laboratory, Bldg. 510, Upton, NY 11973 (United States)
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 (United States)

- Publication Date:

- OSTI Identifier:
- 22663582

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Astrophysical Journal; Journal Volume: 841; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCURACY; CALIBRATION; CORRECTIONS; COSMOLOGY; DETECTION; GALAXIES; GRAVITATIONAL LENSES; NOISE; SIGNAL-TO-NOISE RATIO; SIMULATION

### Citation Formats

```
Sheldon, Erin S., and Huff, Eric M.
```*Practical Weak-lensing Shear Measurement with Metacalibration*. United States: N. p., 2017.
Web. doi:10.3847/1538-4357/AA704B.

```
Sheldon, Erin S., & Huff, Eric M.
```*Practical Weak-lensing Shear Measurement with Metacalibration*. United States. doi:10.3847/1538-4357/AA704B.

```
Sheldon, Erin S., and Huff, Eric M. Sat .
"Practical Weak-lensing Shear Measurement with Metacalibration". United States.
doi:10.3847/1538-4357/AA704B.
```

```
@article{osti_22663582,
```

title = {Practical Weak-lensing Shear Measurement with Metacalibration},

author = {Sheldon, Erin S. and Huff, Eric M.},

abstractNote = {Metacalibration is a recently introduced method to accurately measure weak gravitational lensing shear using only the available imaging data, without need for prior information about galaxy properties or calibration from simulations. The method involves distorting the image with a small known shear, and calculating the response of a shear estimator to that applied shear. The method was shown to be accurate in moderate-sized simulations with galaxy images that had relatively high signal-to-noise ratios, and without significant selection effects. In this work we introduce a formalism to correct for both shear response and selection biases. We also observe that for images with relatively low signal-to-noise ratios, the correlated noise that arises during the metacalibration process results in significant bias, for which we develop a simple empirical correction. To test this formalism, we created large image simulations based on both parametric models and real galaxy images, including tests with realistic point-spread functions. We varied the point-spread function ellipticity at the five-percent level. In each simulation we applied a small few-percent shear to the galaxy images. We introduced additional challenges that arise in real data, such as detection thresholds, stellar contamination, and missing data. We applied cuts on the measured galaxy properties to induce significant selection effects. Using our formalism, we recovered the input shear with an accuracy better than a part in a thousand in all cases.},

doi = {10.3847/1538-4357/AA704B},

journal = {Astrophysical Journal},

number = 1,

volume = 841,

place = {United States},

year = {Sat May 20 00:00:00 EDT 2017},

month = {Sat May 20 00:00:00 EDT 2017}

}