Dark Energy Survey Year 3 Results: Galaxy mock catalogs for BAO analysis

Abstract

The calibration and validation of scientific analysis in simulations is a fundamental tool to ensure unbiased and robust results in observational cosmology. In particular, mock galaxy catalogs are a crucial resource to achieve these goals in the measurement of baryon acoustic oscillation (BAO) in the clustering of galaxies. Here we present a set of 1952 galaxy mock catalogs designed to mimic the Dark Energy Survey Year 3 BAO sample over its full photometric redshift range 0.6 < zphoto < 1.1. The mocks are based upon 488 ICE-COLA fast N-body simulations of full-sky light cones and were created by populating halos with galaxies, using a hybrid halo occupation distribution – halo abundance matching model. This model has ten free parameters, which were determined, for the first time, using an automatic likelihood minimization procedure. We also introduced a novel technique to assign photometric redshift for simulated galaxies, following a two-dimensional probability distribution with VIMOS Public Extragalactic Redshift Survey data. The calibration was designed to match the observed abundance of galaxies as a function of photometric redshift, the distribution of photometric redshift errors, and the clustering amplitude on scales smaller than those used for BAO measurements. An exhaustive analysis was done to ensure that the mocks reproduce the input properties. Finally, mocks were tested by comparing the angular correlation function w(θ), angular power spectrum Cℓ, and projected clustering ξp(r⊥) to theoretical predictions and data. The impact of volume replication in the estimate of the covariance is also investigated. The success in accurately reproducing the photometric redshift uncertainties and the galaxy clustering as a function of redshift render this mock creation pipeline as a benchmark for future analyses of photometric galaxy surveys.

Dark Energy Survey Year 3 results: A 2.7% measurement of baryon acoustic oscillation distance scale at redshift 0.835

“…We create a set of 1952 mock catalogs of the DES Y3 BAO sample that reproduce with high accuracy the principal properties of the data: (i) the sample observational volume, (ii) the abundance of galaxies, true redshift distribution and photometric redshift uncertainty, and (iii) the clustering as a function of redshift. We refer the reader to [40] for further details, and highlight here only the basic features of the ICE-COLA mocks used for this work.…”

“…The replications mentioned above introduce strong correlations among the measured wðθÞ of tomographic bins that are not adjacent. This is discussed more in detail in [40] where it is shown that up to a ∼10% of the particles are repeated (depending on the tomographic bin combination) once we impose the DES Y3 footprint and nðzÞ. This leads to nonzero covariances for tomographic bins that have no redshift overlap otherwise.…”

“…( 8) accounts for linear-theory redshift space distortions [86]. The bias parameters b are obtained by fitting to wðθÞ measurement from the data at three linear bins between 0.5 and 1 degree (see details in [40]). Note that these scales do not contain any BAO information, hence these measurements do not interfere with the blinding scheme.…”

“…The covariances estimated from COLA are not shown in the Fig. 2 and have larger cross-covariance elements due to a replication problem with the mocks, as explained in [40]. We refer the reader to [40] for a comparison between CosmoLike and COLA covariances.…”

“…In [38] we present all the details of the selection of the galaxy sample, that was optimized for z > 0.6 BAO measurements, the tests of its basic properties, the mitigation of observational systematic effects, and the photometric redshift validations, extending what was done in [39]. In [40] we describe the mock catalogs we have developed to test the measurement methods. These mocks match the spatial properties of the data sample and the photo-z resolution.…”