Galaxy clustering, photometric redshifts and diagnosis of systematics in the DES Science Verification data

Abstract

We study the clustering of galaxies detected at i < 22.5 in the Science Verification observations of the Dark Energy Survey (DES). Two-point correlation functions are measured using 2.3 × 10 6 galaxies over a contiguous 116 deg 2 region in five bins of photometric redshift width ∆z = 0.2 in the range 0.2 < z < 1.2. The impact of photometric redshift errors are assessed by comparing results using a template-based photo-z algorithm (BPZ) to a machine-learning algorithm (TPZ). A companion paper (Leistedt et al 2015) presents maps of several observational variables (e.g. seeing, sky brightness) which could modulate the galaxy density. Here we characterize and mitigate systematic errors on the measured clustering which arise from these observational variables, in addition to others such as Galactic dust and stellar contamination. After correcting for systematic effects we measure galaxy bias over a broad range of linear scales relative to mass clustering predicted from the Planck ΛCDM model, finding agreement with CFHTLS measurements with χ 2 of 4.0 (8.7) with 5 degrees of freedom for the TPZ (BPZ) redshifts. We test a "linear bias" model, in which the galaxy clustering is a fixed multiple of the predicted non-linear dark-matter clustering. The precision of the data allow us to determine that the linear bias model describes the observed galaxy clustering to 2.5% accuracy down to scales at least 4 to 10 times smaller than those on which linear theory is expected to be sufficient.

Joint measurement of lensing–galaxy correlations using SPT and DES SV data

“…The tracer galaxy catalog that we use in this work is a subset of the full 'Gold' catalog that was selected by Crocce et al (2016), and which is termed the benchmark selection. Briefly, the benchmark selection restricts the galaxy sample to 18 < i < 22.5, where i is the MAG_AUTO quantity output by SExtractor (Bertin & Arnouts 1996).…”

“…In general, though, DES SV science results have been shown to be quite robust to the choice of photo-z estimation code (e.g. Giannantonio et al 2016;Crocce et al 2016). Tracer and source galaxies are selected on the basis of the z value at which p(z) peaks, z p .…”

“…Although Halofit has been shown to accurately reproduce the galaxy power spectrum at moderately nonlinear scales 6 http://camb.info (e.g. Crocce et al 2016), its predictions become more uncertain at still smaller scales where, for instance, baryonic feedback effects may become large (e.g. Jing et al 2006;van Daalen et al 2011).…”

“…In fact, all of the other possible correlations involving these observables have already been measured by DES and SPT: the shear-shear correlation was measured in The Dark Energy Survey Collaboration et al (2015), the galaxy-galaxy correlation was measured in Crocce et al (2016), and the correlation between CMB κ and galaxy shear was measured in Kirk et al (2015). We have two reasons for restricting the analysis in this work to w κg (θ) and w γ T g (θ).…”

“…The galaxy catalog used here was constructed and tested for systematic effects in Crocce et al (2016) and references therein. The galaxy shear catalog used in this work was extensively tested in Jarvis et al (2015), while galaxy-galaxy lensing measurements and systematics tests were performed in Clampitt et al (2016).…”