Noise from Undetected Sources in Dark Energy Survey Images
Abstract
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. Treating these US as a stationary noise source, we compute a correction to the moment covariance matrix expected from Poisson noise. The corrected covariance matrix matches the moment variances measured on the injected DES images to within 5\%. Thus we have an empirical method to statistically account for US in weak lensing measurements, rather than requiring extremely deep sky simulations. We also find that local sky determinations can remove the bias in flux measurements, at a small penalty in additional, but quantifiable, noise.
Keywords
Cite
@article{arxiv.2004.05618,
title = {Noise from Undetected Sources in Dark Energy Survey Images},
author = {K. Eckert and G. M. Bernstein and A. Amara and A. Amon and A. Choi and S. Everett and D. Gruen and R. A. Gruendl and E. M. Huff and N. Kuropatkin and A. Roodman and E. Sheldon and B. Yanny and Y. Zhang and T. M. C. Abbott and M. Aguena and S. Avila and K. Bechtol and D. Brooks and D. L. Burke and A. Carnero Rosell and M. Carrasco Kind and J. Carretero and M. Costanzi and L. N. da Costa and J. De Vicente and S. Desai and H. T. Diehl and J. P. Dietrich and T. F. Eifler and A. E. Evrard and B. Flaugher and J. Frieman and J. García-Bellido and E. Gaztanaga and J. Gschwend and G. Gutierrez and W. G. Hartley and D. L. Hollowood and K. Honscheid and D. J. James and R. Kron and K. Kuehn and M. A. G. Maia and J. L. Marshall and P. Melchior and F. Menanteau and R. Miquel and R. L. C. Ogando and A. Palmese and F. Paz-Chinchón and A. A. Plazas and A. K. Romer and E. Sanchez and V. Scarpine and S. Serrano and I. Sevilla-Noarbe and M. Smith and M. Soares-Santos and E. Suchyta and M. E. C. Swanson and G. Tarle and D. Thomas and T. N. Varga and A. R. Walker and W. Wester and R. D. Wilkinson and J. Zuntz and the DES Collaboration},
journal= {arXiv preprint arXiv:2004.05618},
year = {2020}
}
Comments
13 pages, 10 figures