[Paper Review] Galaxy Clustering in Harmonic Space from the Dark Energy Survey Year 1 Data: Compatibility with Real-Space Results

F. Andrade-Oliveira|arXiv (Cornell University)|Jan 1, 2021

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy57 references13 citations

TL;DR

This paper develops and validates a harmonic-space analysis pipeline for galaxy clustering using Dark Energy Survey Year 1 (DES-Y1) data, demonstrating compatibility with prior real-space results. By adapting real-space products—including redshift binning, survey masks, and weight maps—the authors show that harmonic-space angular power spectrum measurements yield consistent linear galaxy bias constraints, paving the way for future 3x2-point analyses in harmonic space for DES-Y3 and other surveys.

ABSTRACT

We perform an analysis in harmonic space of the Dark Energy Survey Year 1 Data (DES-Y1) galaxy clustering data using products obtained for the real-space analysis. We test our pipeline with a suite of lognormal simulations, which are used to validate scale cuts in harmonic space as well as to provide a covariance matrix that takes into account the DES-Y1 mask. We then apply this pipeline to DES-Y1 data taking into account survey property maps derived for the real-space analysis. We compare with real-space DES-Y1 results obtained from a similar pipeline. We show that the harmonic space analysis we develop yields results that are compatible with the real-space analysis for the bias parameters. This verification paves the way to performing a harmonic space analysis for the upcoming DES-Y3 data.

Motivation & Objective

• To develop a robust pipeline for cosmological parameter estimation using galaxy clustering in harmonic space from DES-Y1 data.
• To validate the pipeline using lognormal simulations that replicate DES-Y1 survey geometry and systematics.
• To compare harmonic-space results with the established real-space analysis from DES-Y1 to test consistency.
• To adapt scale cuts and covariance matrices from real-space to harmonic space, evaluating their impact on bias constraints.
• To enable future 3x2-point analyses in harmonic space for upcoming DES-Y3 data.

Proposed method

• Adapts real-space analysis products—galaxy sample, survey masks, and weight maps—for use in harmonic-space analysis of galaxy clustering.
• Employs the pseudo-Cℓ method to compute angular power spectra on a masked sky, accounting for mode coupling.
• Generates lognormal simulations to test scale cuts and estimate the covariance matrix, incorporating the DES-Y1 survey mask.
• Uses CosmoSIS to estimate cosmological parameters, with a fiducial ΛCDM cosmology matching the DES-Y1 real-space analysis.
• Applies two types of scale cuts—'naive' (configurational) and 'physical' (based on angular scale mapping)—to assess robustness.
• Compares constraints from two covariance matrix sources: FLASK and CosmoLike, to assess reliability.

Experimental results

Research questions

• RQ1 Can a harmonic-space analysis of galaxy clustering in DES-Y1 data produce results consistent with the established real-space analysis?
• RQ2 How do scale cuts derived from real-space analysis map into harmonic space, and which mapping yields more consistent results?
• RQ3 Do different covariance matrix estimators (FLASK vs. CosmoLike) produce comparable constraints on galaxy bias?
• RQ4 Is the harmonic-space pipeline robust and reliable enough to be applied to future DES-Y3 data?
• RQ5 Can the same survey systematics and weight maps used in real-space be effectively repurposed for harmonic-space analysis?

Key findings

• The harmonic-space analysis produces galaxy bias constraints that are statistically compatible with the real-space results from Elvin-Poole et al. (2018).
• The 'physical scale cut' approach—derived from mapping real-space scale cuts to angular scales—yields results more consistent with the real-space analysis than the 'naive' cut.
• Covariance matrices from FLASK and CosmoLike produce very similar constraints, indicating robustness of the pipeline.
• The pipeline successfully handles survey systematics and mask effects using the same products from the real-space analysis, validating reusability.
• The results confirm that harmonic-space analysis is a viable alternative to real-space analysis for DES-Y1-like data, with potential for future 3x2-point analyses.
• The study establishes a foundation for future multi-probe cosmological analyses using angular power spectra in both real and harmonic spaces.