Publications

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Taming Additive Systematics via Redshift-Bin-Optimized Star-Galaxy Separation

Contamination from stars in the galaxy samples of large-scale structure surveys can bias cosmological constraints if not tightly controlled. This is especially true for lens samples used for galaxy clustering and galaxy-galaxy lensing probes, where contamination is a primary source of additive systematics. We propose an improved approach to star-galaxy separation and an optimal weighting scheme to jointly mitigate additive and multiplicative contamination of the density field at the map level. O…

N. Weaverdyck, D. Schlegel, A. Raichoor, I. Sevilla-Noarbe (2026). Taming Additive Systematics via Redshift-Bin-Optimized Star-Galaxy Separation. Submitted.

Steeling Weak Lensing Source Galaxy Samples against Systematics using Wide Field Spectroscopy

We investigate the cosmological constraining power of combined weak galaxy lensing and galaxy clustering probes, i.e. $3\times2$-point analyses, assuming flexible models for redshift uncertainty, and Lagrangian perturbation theory and hybrid effective field theory models for galaxy intrinsic alignments, galaxy bias and baryonic physics. In this context, we provide a detailed accounting of the limiting systematics on $3\times2$-point analyses. Our main finding is that in the presence of current l…

J. DeRose, N. Weaverdyck, M. White, Shi-Fan Chen, D. Schlegel, A. Slosar (2026). Steeling Weak Lensing Source Galaxy Samples against Systematics using Wide Field Spectroscopy. Submitted.

Dark Energy Survey Year 6 Results: MagLim++ Lens Sample Selection and Measurements of Galaxy Clustering

Galaxy clustering is a sensitive probe of the expansion history and growth of structure of the universe, and key degeneracies can be broken by combining these data with measurements of cosmic shear and galaxy-galaxy lensing (a so-called 3$\times$2pt analysis). The largest and least biased statistical samples of galaxies for use in clustering analyses can be collected photometrically through large imaging surveys. However, selecting clean photometric subsamples for cosmology are crucial for avoid…

N. Weaverdyck, M. Rodr'iguez-Monroy, et al. (2026). Dark Energy Survey Year 6 Results: MagLim++ Lens Sample Selection and Measurements of Galaxy Clustering. Submitted.
arXiv

The Compilation and Validation of the Spectroscopic Redshift Catalogs for the DESI-COSMOS and DESI-XMM-LSS Fields

Over several dedicated programs that include targets beyond the main cosmological samples, the Dark Energy Spectroscopic Instrument collected spectra for 304,970 unique objects in two fields centered on the COSMOS and XMM-LSS fields. In this work, we develop spectroscopic redshift robustness criteria for those spectra, validate these criteria using visual inspection, and provide two custom value-added catalogs with our redshift characterizations. With these criteria, we reliably classify 212,935…

J. Ratajczak, K. Dawson, N. Weaverdyck, et al. (2025). The Compilation and Validation of the Spectroscopic Redshift Catalogs for the DESI-COSMOS and DESI-XMM-LSS Fields. The Astronomical Journal.
arXiv | Download Paper

Dark Energy Survey Year 6 Results: improved mitigation of spatially varying observational systematics with masking

As photometric surveys reach unprecedented statistical precision, systematic uncertainties increasingly dominate large-scale structure probes relying on galaxy number density. Defining the final survey footprint is critical, as it excludes regions affected by artefacts or suboptimal observing conditions. For galaxy clustering, spatially varying observational systematics, such as seeing, are a leading source of bias. Template maps of contaminants are used to derive spatially dependent corrections…

M. Rodr'iguez-Monroy, N. Weaverdyck, et al. (2025). Dark Energy Survey Year 6 Results: improved mitigation of spatially varying observational systematics with masking. Submitted.
arXiv

Robust sampling for weak lensing and clustering analyses with the dark energy survey

Recent cosmological analyses rely on the ability to accurately sample from high-dimensional posterior distributions. A variety of algorithms have been applied in the field, but justification of the particular sampler choice and settings is often lacking. Here we investigate three such samplers to motivate and validate the algorithm and settings used for the Dark Energy Survey (DES) analyses of the first 3 years (Y3) of data from combined measurements of weak lensing and galaxy clustering. We emp…

P. Lemos, N. Weaverdyck, et al. (2022). Robust sampling for weak lensing and clustering analyses with the dark energy survey. Monthly Notices of the Royal Astronomical Society.
arXiv | Download Paper

Dark Energy Survey Year 3 results: Constraints on extensions to ΛCDM with weak lensing and galaxy clustering

We constrain extensions to the $\Lambda$CDM model using measurements from the Dark Energy Survey's first three years of observations and external data. The DES data are the two-point correlation functions of weak gravitational lensing, galaxy clustering, and their cross-correlation. We use simulated data and blind analyses of real data to validate the robustness of our results. In many cases, constraining power is limited by the absence of nonlinear predictions that are reliable at our requi…

D. C. T. Abbott et al. (2022). Dark Energy Survey Year 3 results: Constraints on extensions to ΛCDM with weak lensing and galaxy clustering. Physical Review D.
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Dark Energy Survey Year 3 Results: Galaxy clustering and systematics treatment for lens galaxy samples

In this work we present the galaxy clustering measurements of the two DES lens galaxy samples: a magnitude-limited sample optimized for the measurement of cosmological parameters, MagLim, and a sample of luminous red galaxies selected with the redMaGiC algorithm. MagLim / redMaGiC sample contains over 10 million / 2.5 million galaxies and is divided into six / five photometric redshift bins spanning the range z ∈ [0.20, 1.05] / z ∈ [0.15, 0.90]. Both samples cover 4143 $\deg ^2$ over which we pe…

M. Rodr'iguez-Monroy, N. Weaverdyck, et al. (2021). Dark Energy Survey Year 3 Results: Galaxy clustering and systematics treatment for lens galaxy samples. Monthly Notices of the Royal Astronomical Society.
arXiv | Download Paper

Mitigating contamination in LSS surveys: a comparison of methods

Future large scale structure surveys will measure the locations and shapes of billions of galaxies. The precision of such catalogs will require meticulous treatment of systematic contamination of the observed fields. We compare several existing methods for removing such systematics from galaxy clustering measurements. We show how all the methods, including the popular pseudo-$C_\ell$ Mode Projection and Template Subtraction methods, can be interpreted under a common regression framework and use …

N. Weaverdyck, D. Huterer (2020). Mitigating contamination in LSS surveys: a comparison of methods. arXiv: Cosmology and Nongalactic Astrophysics.
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Differential Assessment, Differential Benefit: Four-year Problem Roulette Analysis of STEM Practice Study

Using five million responses to thousands of practice examination questions on an optional study service known as Problem Roulette, we explore subject-specific differences in assessment style, grade benefit from usage of the service, and differential features in study behavior and grade outcome by birth sex. Our study includes more than 20,000 students enrolled in eight terms of introductory courses in general chemistry, physics and statistics. Student responses in the space of accuracy and resp…

N. Weaverdyck, D. Anbajagane, A. Evrard (2020). Differential Assessment, Differential Benefit: Four-year Problem Roulette Analysis of STEM Practice Study. Proceedings of the Seventh ACM Conference on Learning @ Scale.
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The Quest for the Inflationary Spectral Runnings in the Presence of Systematic Errors

Cosmological inflation predicts that the scalar spectral index “runs” with scale. Constraints on the values of the spectral runnings, and , therefore provide a fundamental test of the physics of inflation. Here, we study the feasibility of measuring the runnings when information from upcoming large-volume galaxy surveys is used to supplement the information provided by a cosmic microwave background (CMB)-S4 experiment, particularly focusing on the effect of including high-k, nonlinear scales. Si…

Xiaolei Li, N. Weaverdyck, S. Adhikari, D. Huterer, J. Muir, Hao-Yi Wu (2018). The Quest for the Inflationary Spectral Runnings in the Presence of Systematic Errors. The Astrophysical Journal.
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Integrated Sachs-Wolfe map reconstruction in the presence of systematic errors

The decay of gravitational potentials in the presence of dark energy leads to an additional, late-time contribution to anisotropies in the cosmic microwave background (CMB) at large angular scales. The imprint of this so-called integrated Sachs-Wolfe (ISW) effect to the CMB angular power spectrum has been detected and studied in detail, but reconstructing its spatial contributions to the CMB $\textit{map}$, which would offer the tantalizing possibility of separating the early- from the late-time…

N. Weaverdyck, J. Muir, D. Huterer (2017). Integrated Sachs-Wolfe map reconstruction in the presence of systematic errors. Physical Review D.
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Noah Weaverdyck

Publications

Select publications with leading contributions