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.

arXiv comment13 pages, 10 figures

References in corpus (20)

• A Method for Weak Lensing Observations
• Improved background subtraction for the Sloan Digital Sky Survey images
• Practical Weak Lensing Shear Measurement with Metacalibration
• The Dark Energy Survey Image Processing Pipeline
• Dark Energy Survey Year 1 Results: Weak Lensing Shape Catalogues
• Tracing the first stars with cosmic infrared background fluctuations
• The DES Science Verification Weak Lensing Shear Catalogues
• Metacalibration: Direct Self-Calibration of Biases in Shear Measurement
• New measurements of the cosmic infrared background fluctuations in deep Spitzer/IRAC survey data and their cosmological implications
• IM3SHAPE: A maximum-likelihood galaxy shear measurement code for cosmic gravitational lensing
• No galaxy left behind: accurate measurements with the faintest objects in the Dark Energy Survey
• Bayesian Lensing Shear Measurement
• The Opacity of Spiral Galaxy Disks IV: Radial Extinction Profiles from Counts of Distant Galaxies seen through Foreground Disks
• A study of the sensitivity of shape measurements to the input parameters of weak lensing image simulations
• An accurate and practical method for inference of weak gravitational lensing from galaxy images
• Euclid Preparation IV. Impact of undetected galaxies on weak-lensing shear measurements
• Dark Energy Survey Year 1 Results: The Impact of Galaxy Neighbours on Weak Lensing Cosmology with im3shape
• HERschel Observations of Edge-on Spirals (HEROES). I: Far-infrared morphology and dust mass determination
• Weak-lensing shear measurement with machine learning: teaching artificial neural networks about feature noise
• Constraining the luminosity function of faint undetected i-dropout galaxies

Cited by in corpus (9)

• Dark Energy Survey Year 3 Results: Cosmology from Cosmic Shear and Robustness to Modeling Uncertainty
• The Dark Energy Survey Data Release 2
• KiDS-1000 catalogue: Weak gravitational lensing shear measurements
• Dark Energy Survey Year 3 Results: Measuring the Survey Transfer Function with Balrog
• Is diffuse intracluster light a good tracer of the galaxy cluster matter distribution?
• Mitigating the effects of undersampling in weak lensing shear estimation with metacalibration
• The PAU survey: Estimating galaxy photometry with deep learning
• Analytical Weak-lensing Shear Responses of Galaxy Properties and Galaxy Detection
• Synthetic Galaxy Clusters and Observations Based on Dark Energy Survey Year 3 Data