Dark Energy Survey Year 3 Results: Optimizing the Lens Sample in Combined Galaxy Clustering and Galaxy-Galaxy Lensing Analysis

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, z phot , and benchmark the potential gains against those using the well established REDMAGIC [1] 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 < 4 z phot + 18 and has ∼ 30% wider redshift distributions but ∼ 3.5 times more galaxies than REDMAGIC. Assuming a wCDM model 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.

Dark Energy Survey Year 3 Results: Calibration of Lens Sample Redshift Distributions using Clustering Redshifts with BOSS/eBOSS

“…The Gold catalog covers the full DES footprint of nearly 5000 deg 2 , and contains around 388 million objects. The two samples are used for cosmological analyses in DES Collaboration (prep) are described in detail in Rodríguez-Monroy et al (prep) and Porredon et al (2020). We repeat some of the main information about each sample here.…”

“…The DES M L samples are described in Porredon et al (2020). They are created using a redshift-dependent magnitude cut, with the redshift estimate for each galaxy coming from the DNF (De In shaded outline, we show the BOSS 𝑛(𝑧) used in the Year-1 analysis of Cawthon et al (2018).…”

Dark Energy Survey Year 3 Results: Measuring the Survey Transfer Function with Balrog

“…In Elvin-Poole et al (2020) this Balrog methodology is applied to the lens samples used in the DES Y3 analysis including more complex color cuts and tomographic redshift binning. In this analysis, the maglim lens sample (Porredon et al 2020), which has a redshift dependent magnitude limit and tomographic binning, is found to have a C sample from approximately 2 to 5 from low to high redshift. The redMaGiC lens sample (Rozo et al 2016) strong (2014) on Balrog detections across 48 tiles, the variance of measured galaxy moments was found to be up to 30% in excess of Poisson predictions in Eckert et al (2020).…”

“…Here we estimate the approximate impact on the clustering signal due to systematic differences between Balrog and Y3 GOLD for a sample broadly similar to the maglim science sample described in Porredon et al (2020), where we cut both the Y3 GOLD and Balrog samples to 17.5 < i < 21.5 in addition to the previous cuts. We make density maps based on each property map across the full Y3 GOLD footprint by interpolating the trends in Balrog and GOLD to fill in cells where we do not have injection samples.…”

Bright galaxy sample in the Kilo-Degree Survey Data Release 4: selection, photometric redshifts, and physical properties

“…Such samples can be enhanced with deeper, yet less complete, photometric selections of luminous red galaxies (e.g. Rozo et al 2016;Vakili et al 2020) and adaptive magnitude cuts as a function of photo-z (Porredon et al 2020) to probe a larger range of lens redshifts and luminosities. In particular, the CSMF of central galaxies is modeled as a log-normal,…”