Dark Energy Survey Year 3 results: Optimizing the lens sample in a combined galaxy clustering and galaxy-galaxy lensing analysis

Porredon, A. and Crocce, M. and Fosalba, P. and Elvin-Poole, J. and Carnero Rosell, A. and Cawthon, R. and Eifler, T. F. and Fang, X. and Ferrero, I. and Krause, E. and MacCrann, N. and Weaverdyck, N. and Abbott, T. M. C. and Aguena, M. and Allam, S. and Amon, A. and Avila, S. and Bacon, D. and Bertin, E. and Bhargava, S. and Bridle, S. L. and Brooks, D. and Carrasco Kind, M. and Carretero, J. and Castander, F. J. and Choi, A. and Costanzi, M. and da Costa, L. N. and Pereira, M. E. S. and De Vicente, J. and Desai, Shantanu and Diehl, H. T. and Doel, P. and Drlica-Wagner, A. and Eckert, K. and Ferté, A. and Flaugher, B. and Frieman, J. and García-Bellido, J. and Gaztanaga, E. and Gerdes, D. W. and Giannantonio, T. and Gruen, D. and Gruendl, R. A. and Gschwend, J. and Gutierrez, G. and Hartley, W. G. and Hinton, S. R. and Hollowood, D. L. and Honscheid, K. and Hoyle, B. and James, D. J. and Jarvis, M. and Kuehn, K. and Kuropatkin, N. and Maia, M. A. G. and Marshall, J. L. and Menanteau, F. and Miquel, R. and Morgan, R. and Palmese, A. and Pandey, S. and Paz-Chinchón, F. and Plazas, A. A. and Rodriguez-Monroy, M. and Roodman, A. and Samuroff, S. and Sanchez, E. and Scarpine, V. and Serrano, S. and Sevilla-Noarbe, I. and Smith, M. and Soares-Santos, M. and Suchyta, E. and Swanson, M. E. C. and Tarle, G. and To, C. and Varga, T. N. and Weller, J. and Wilkinson, R. D. (2021) Dark Energy Survey Year 3 results: Optimizing the lens sample in a combined galaxy clustering and galaxy-galaxy lensing analysis. Physical Review D, 103 (4). ISSN 2470-0010

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Abstract

We investigate potential gains in cosmological constraints from the combination of galaxy clustering and galaxy-galaxy lensing by optimizing the lens galaxy sample selection using information from Dark Energy Survey (DES) Year 3 data and assuming the DES Year 1 metacalibration sample for the sources. We explore easily reproducible selections based on magnitude cuts in i-band as a function of (photometric) redshift, zphot, and benchmark the potential gains against those using the well-established redMaGiC [E. Rozo et al., Mon. Not. R. Astron. Soc. 461, 1431 (2016)MNRAA40035-871110.1093/mnras/stw1281] sample. We focus on the balance between density and photometric redshift accuracy, while marginalizing over a realistic set of cosmological and systematic parameters. Our optimal selection, the MagLim sample, satisfies i<4zphot+18 and has ∼30% wider redshift distributions but ∼3.5 times more galaxies than redMaGiC. Assuming a wCDM model (i.e. with a free parameter for the dark energy equation of state) and equivalent scale cuts to mitigate nonlinear effects, this leads to 40% increase in the figure of merit for the pair combinations of ωm, w, and σ8, and gains of 16% in σ8, 10% in ωm, and 12% in w. Similarly, in ΛCDM, we find an improvement of 19% and 27% on σ8 and ωm, respectively. We also explore flux-limited samples with a flat magnitude cut finding that the optimal selection, i<22.2, has ∼7 times more galaxies and ∼20% wider redshift distributions compared to MagLim, but slightly worse constraints. We show that our results are robust with respect to the assumed galaxy bias and photometric redshift uncertainties with only moderate further gains from increased number of tomographic bins or the inclusion of bin cross-correlations, except in the case of the flux-limited sample, for which these gains are more significant.

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