Day 1216

Friday.

1702.02600
Metacalibration: direct self-calibration of biases in shear measurement
Huff, Mandelbaum

One of the primary limiting sources of systematic uncertainty in forthcoming WL measurements is systematic uncertainty in the quantitative relationship between the distortions due to gravitational lensing and the measurable properties of galaxy images.  Present a statistically principled, general solution to this problem.  The technique infers multiplicative shear calibration parameters by modifying the actual survey data to simulate the effects of a known shear.  It can be applied to any shear estimation method based on weighted averages of galaxy shape measurements, which includes all methods used to date for shear estimation with real data.  Use of the real images mitigates uncertainty due to unknown galaxy morphology, which is a serious concern for calibration of shear estimates based on image simulations.  Test results on simulated images from the GREAT3 challenge, and show that the method eliminates calibration biases for several different shape measurement techniques at the level of precision measurable with the GERAT3 sims (a few tenths of a percent).


1702.02601
Practical weak lensing shear measurement with metacalibration
Sheldon, Huff

Metacalibration is a recently introduced method to accurately measure WL 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 sims with relatively high S/N galaxy images, and without significant selection effects.  In this work, introduce a formalism to correct for both shear response and selection biases.  Also observe that, for relatively low S/N images, the correlated noise that arises during the metacalibration process results in significant bias, for which a simple empirical correction is developed.