Implications of a wavelengthdependent PSF for weak lensing measurements
Abstract
The convolution of galaxy images by the point spread function (PSF) is the dominant source of bias for weak gravitational lensing studies, and an accurate estimate of the PSF is required to obtain unbiased shape measurements. The PSF estimate for a galaxy depends on its spectral energy distribution (SED), because the instrumental PSF is generally a function of the wavelength. In this paper we explore various approaches to determine the resulting `effective' PSF using broadband data. Considering the Euclid mission as a reference, we find that standard SED template fitting methods result in biases that depend on source redshift, although this may be remedied if the algorithms can be optimized for this purpose. Using a machine learning algorithm we show that, at least in principle, the required accuracy can be achieved with the current survey parameters. It is also possible to account for the correlations between photometric redshift and PSF estimates that arise from the use of the same photometry. We explore the impact of errors in photometric calibration, errors in the assumed wavelength dependence of the PSF model, and limitations of the adopted template libraries. Our results indicate that the required accuracy for Euclid can be achieved using the data that are planned to determine photometric redshifts.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 July 2018
 DOI:
 10.1093/mnras/sty830
 arXiv:
 arXiv:1707.04334
 Bibcode:
 2018MNRAS.477.3433E
 Keywords:

 gravitational lensing: weak;
 methods: data analysis;
 space vehicles: instruments;
 cosmological parameters;
 cosmology: observations;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 doi:10.1093/mnras/sty830