Noise from Undetected Sources in Dark Energy Survey Images

Understand

For ground-based optical imaging with current CCD technology, the Poisson fluctuations in source and sky background photon arrivals dominate the noise budget and are readily estimated.

• Another component of noise, however, is the signal from the undetected population of stars and galaxies.
• Using injection of artificial galaxies into images, we demonstrate that the measured variance of galaxy moments (used for weak gravitational lensing measurements) in Dark Energy Survey (DES) images is significantly in excess of the Poisson predictions, by up to 30\%, and that the background sky levels are overestimated by current software.
• By cross-correlating distinct images of "empty" sky regions, we establish that there is a significant image noise contribution from undetected static sources (US), which on average are mildly resolved at DES resolution.