Image Simulations for Testing the Fidelity of SKYSURF Background Measurement Algorithms

The goal of Hubble Space Telescope Cycle 27–29 Archival Legacy project “SKYSURF” is to measure the panchromatic sky surface brightness and source catalogs from all archival HST ACS and WFC3 images since the launch of these instruments by the Space Shuttle—more than 57,000 images in total since 2002. All SKYSURF images together will measure the panchromatic Zodiacal brightness, the Diffuse Galactic Light, and the Extragalactic Background Light. SKYSURF will significantly constrain the various amounts of diffuse light in the universe with major ramifications for cosmic star formation and planet formation.<br/><br/>Several sky background measurement algorithms are capable of measuring the background levels of images in the SKYSURF database. To test the fidelity of these sky background measurement algorithms, images with known sky background and noise levels were necessary to determine quantitatively how far a sky measurement algorithm strays from the true value. For this purpose, I developed an algorithm that could create simulated images for filter F125W of the WFC3/IR instrument on the Hubble Space Telescope (HST). Filter F125W was selected because the Extragalactic Background Light is brightest in this wavelength band; moreover, the COBE Zodiacal light measurement is also at 1.25 microns. The simulated images created contain stars, galaxies, cosmic rays, and light gradients. We discuss here how these simulated images were made and the different kinds of simulated images that were produced.