Impact of point spread function higher moments error on weak gravitational lensing – II. A comprehensive study

Xinzhong

Res. Astron. Astrophys.

et al. 2023

The weak gravitational lensing is a powerful tool in modern cosmology. To accurately measure the weak lensing signal, one has to control the systematic bias to a small level. One of the most difficult problems is how to correct the smearing effect of the Point Spread Function (PSF) on the shape of the galaxies. The chromaticity of PSF for a broad-band observation can lead to new subtle effects. Since the PSF is wavelength dependent and the spectrum energy distribution between stars and galaxies is different, the effective PSF measured from the star images will be different from that smears the galaxies. Such a bias is called colour bias. We estimate it in the optical bands of the Chinese Space Station Survey Telescope from simulated PSFs, and show the dependence on the colour and redshift of the galaxies. Moreover, due to the spatial variation of spectra over the galaxy image, there exists another higher-order bias, colour gradient bias. Our results show that both colour bias and colour gradient bias are generally below 0.1 percent in CSST. Only for small-size galaxies, one needs to be careful about the colour gradient bias in the weak lensing analysis using CSST data.

Section: Color Bias With Color and Redshiftmentioning

confidence: 85%

The Chromatic Point-spread Function of Weak Lensing Measurement in the Chinese Space Station Survey Telescope

Xinzhong

Res. Astron. Astrophys.

et al. 2023

“…We also anticipate that bluer bands will experience an augmented BFE due to a shorter photon conversion depth within the sensor, thereby resulting in a strengthened BFE from the increased drift length (observed by Astier & Regnault 2023, in HSC and ongoing work to measure the effect in LSSTCam sensors). In addition, higher-order radial moment errors in the PSF are known to also impact WL observables, which is also a subject of future investigation (Zhang et al 2021;Zhang et al 2022).…”

Section: Future Workmentioning

confidence: 98%

Mitigation of the Brighter-fatter Effect in the LSST Camera

Broughton,

Utsumi,

Plazas Malagón

et al. 2024

PASP

Thick, fully depleted charge-coupled devices are known to exhibit nonlinear behavior at high signal levels due to the dynamic behavior of charges collecting in the potential wells of pixels, called the brighter-fatter effect (BFE). The effect results in distorted images of bright calibration stars, creating a flux-dependent point-spread function that if left unmitigated, could make up a large fraction of the error budget in Stage IV weak-lensing (WL) surveys such as the Legacy Survey of Space and Time (LSST). In this paper, we analyze image measurements of flat fields and artificial stars taken at different illumination levels with the LSST Camera (LSSTCam) at SLAC National Accelerator Laboratory in order to quantify this effect in the LSSTCam before and after a previously introduced correction technique. We observe that the BFE evolves anisotropically as a function of flux due to higher-order BFEs, which violates the fundamental assumption of this correction method. We then introduce a new method based on a physically motivated model to account for these higher-order terms in the correction, and then we test the modified correction on both data sets. We find that the new method corrects the effect in flat fields better than it corrects the effect in artificial stars, which we suggest is the result of sub-pixel physics not included in this correction model. We use these results to define a new metric for the full-well capacity of our sensors and advise image processing strategies to further limit the impact of the effect on LSST WL science pathways.

“…In addition, faint star images generally are inappropriate for PSF modelings (Paulin-Henriksson et al 2009;Zhang et al 2022). In order to use as many stars as possible for PSF modeling, we choose stamps that have signal-to-noise ratios (S/Ns) larger than 10 as PSF star candidates.…”

Section: Data Reduction and Star Image Selectionmentioning

confidence: 99%

HybPSF: Hybrid Point-spread Function Reconstruction for the Observed JWST NIRCam Image

Nie,

Shan,

et al. 2024

The James Webb Space Telescope (JWST) marks a new era of astronomical observation and discovery, providing unrivaled precision in various measurements, including photometry, morphology, and shear measurement. Accurate point-spread function (PSF) models are essential for many of these measurements. In this paper, we introduce HybPSF, a hybrid PSF construction method for JWST NIRCam imaging data that combines the WebbPSF software, which simulates the PSF for JWST, with observed data to produce more accurate and reliable PSF models. We apply this method to the SMACS J0723 imaging data and construct supplementary structures from residuals obtained by subtracting the WebbPSF PSF model from the data. Our results show that HybPSF significantly reduces discrepancies between the PSF model and the data compared to WebbPSF. Specifically, the PSF shape parameter ellipticity and size comparisons indicate that HybPSF improves precision by approximately 10 times for R 2 and 50% for e. This improvement has important implications for astronomical measurements using JWST NIRCam imaging data.