Near-IR Weak-lensing (NIRWL) Measurements in the CANDELS Fields. I. Point-spread Function Modeling and Systematics

We have undertaken a near-IR weak-lensing (NIRWL) analysis of the CANDELS HST/WFC3-IR F160W observations. With the Gaia proper motion-corrected catalog as an astrometric reference, we updated the astrometry of the five CANDELS mosaics and achieved an absolute alignment within 002 +/- 002, on average, which is a factor of several superior to existing mosaics. These mosaics are available to download (https://drive.google.com/drive/folders/1k9WEV3tBOuRKBlcaTJ0-wTZnUCisS__r). We investigated the systematic effects that need to be corrected for weak-lensing measurements. We find that the largest contributing systematic effect is caused by undersampling. We find a subpixel centroid dependence on the PSF shape that causes the PSF ellipticity and size to vary by up to 0.02% and 3%, respectively. Using the UDS as an example field, we show that undersampling induces a multiplicative shear bias of -0.025. We find that the brighter-fatter effect causes a 2% increase in the size of the PSF and discover a brighter-rounder effect that changes the ellipticity by 0.006. Based on the small range of slopes in a galaxy's spectral energy distribution (SED) within the WFC3-IR bandpasses, we suggest that the impact of the galaxy SED on the PSF is minor. Finally, we model the PSF of WFC3-IR F160W for weak lensing using a principal component analysis. The PSF models account for temporal and spatial variations of the PSF. The PSF corrections result in residual ellipticities and sizes, divided by de(1)divided by < 0.0005 +/- 0.0003, divided by de(2)divided by < 0.0005 +/- 0.0003, and divided by dR divided by < 0.0005 +/- 0.0001, that are sufficient for the upcoming NIRWL search for massive overdensities in the five CANDELS fields.

Automated summary

In this study, a near-IR weak-lensing analysis of CANDELS HST/WFC3-IR F160W observations was conducted, with updated astrometry of the mosaics achieving absolute alignment with a high degree of accuracy. Systematic effects in weak-lensing measurements were investigated, highlighting undersampling as a major contributing factor. PSF modeling for weak lensing using principal component analysis was performed, resulting in corrections that are sufficient for future NIRWL searches in the CANDELS fields.