SKYSURF-7: Exploring PSF Contamination in Diffuse Sky Measurements with HST

Abstract Project SKYSURF constrains Extragalactic Background Light and diffuse light using over 200,000 images in the Hubble Space Telescope (HST) archive. However, it is possible that the faint wings of the point-spread function (PSF), which characterizes the distribution of light in individual stars and galaxies in an image, could contaminate or skew measurements of the sky surface brightness (sky-SB). Using the HST Wide Field Camera 3/IR F140W filter, we investigate whether a realistic HST PSF contaminates SKYSURF sky-SB measurements. Using the image simulation tool GalSim we characterize potential PSF contamination by comparing a simplistic modeled Gaussian PSF and a more realistic empirical HST PSF. We find PSF contamination is negligible for our sky-SB measurements, calculating a contribution of 0.00054 MJy sr −1 due to PSF contamination, compared to current measurement uncertainties of 0.005 MJy sr −1 .