Dark Energy Survey Year 3 Results: Measuring the Survey Transfer Function with Balrog
Abstract
We describe an updated calibration and diagnostic framework, Balrog, used to directly sample the selection and photometric biases of the Dark Energy Survey's (DES) Year 3 (Y3) dataset. We systematically inject onto the single-epoch images of a random 20% subset of the DES footprint an ensemble of nearly 30 million realistic galaxy models derived from DES Deep Field observations. These augmented images are analyzed in parallel with the original data to automatically inherit measurement systematics that are often too difficult to capture with traditional generative models. The resulting object catalog is a Monte Carlo sampling of the DES transfer function and is used as a powerful diagnostic and calibration tool for a variety of DES Y3 science, particularly for the calibration of the photometric redshifts of distant "source" galaxies and magnification biases of nearer "lens" galaxies. The recovered Balrog injections are shown to closely match the photometric property distributions of the Y3 GOLD catalog, particularly in color, and capture the number density fluctuations from observing conditions of the real data within 1% for a typical galaxy sample. We find that Y3 colors are extremely well calibrated, typically within ~1-8 millimagnitudes, but for a small subset of objects we detect significant magnitude biases correlated with large overestimates of the injected object size due to proximity effects and blending. We discuss approaches to extend the current methodology to capture more aspects of the transfer function and reach full coverage of the survey footprint for future analyses.
Keywords
Cite
@article{arxiv.2012.12825,
title = {Dark Energy Survey Year 3 Results: Measuring the Survey Transfer Function with Balrog},
author = {S. Everett and B. Yanny and N. Kuropatkin and E. M. Huff and Y. Zhang and J. Myles and A. Masegian and J. Elvin-Poole and S. Allam and G. M. Bernstein and I. Sevilla-Noarbe and M. Splettstoesser and E. Sheldon and M. Jarvis and A. Amon and I. Harrison and A. Choi and W. G. Hartley and A. Alarcon and C. Sánchez and D. Gruen and K. Eckert and J. Prat and M. Tabbutt and V. Busti and M. R. Becker and N. MacCrann and H. T. Diehl and D. L. Tucker and E. Bertin and T. Jeltema and A. Drlica-Wagner and R. A. Gruendl and K. Bechtol and A. Carnero Rosell and T. M. C. Abbott and M. Aguena and J. Annis and D. Bacon and S. Bhargava and D. Brooks and D. L. Burke and M. Carrasco Kind and J. Carretero and F. J. Castander and C. Conselice and M. Costanzi and L. N. da Costa and M. E. S. Pereira and J. De Vicente and J. DeRose and S. Desai and T. F. Eifler and A. E. Evrard and I. Ferrero and P. Fosalba and J. Frieman and J. García-Bellido and E. Gaztanaga and D. W. Gerdes and G. Gutierrez and S. R. Hinton and D. L. Hollowood and K. Honscheid and D. Huterer and D. J. James and S. Kent and E. Krause and K. Kuehn and O. Lahav and M. Lima and H. Lin and M. A. G. Maia and J. L. Marshall and P. Melchior and F. Menanteau and R. Miquel and J. J. Mohr and R. Morgan and J. Muir and R. L. C. Ogando and A. Palmese and F. Paz-Chinchón and A. A. Plazas and M. Rodriguez-Monroy and A. K. Romer and A. Roodman and E. Sanchez and V. Scarpine and S. Serrano and M. Smith and M. Soares-Santos and E. Suchyta and M. E. C. Swanson and G. Tarle and C. To and M. A. Troxel and T. N. Varga and J. Weller and R. D. Wilkinson},
journal= {arXiv preprint arXiv:2012.12825},
year = {2022}
}
Comments
Version accepted by ApJS. See https://www.darkenergysurvey.org/des-year-3-cosmology-results-papers/ for the full DES Y3 cosmology release. 59 pages, 32 figures