The DECADE cosmic shear project I: A new weak lensing shape catalog of 107 million galaxies

TL;DR

We address cosmic shear measurements with a new DECADE weak-lensing catalog built from 107 million DECam galaxies over 5{,}412 deg$^2$, processed with the DESDM pipeline and shapes calibrated via Metacalibration. The work details data processing, base catalog construction, and a rigorous suite of empirical tests plus an image-simulation pipeline to quantify shear calibration biases, providing per-bin multiplicative biases around $m \sim -2.5\%$ and additive biases at the $10^{-4}$ level. The results demonstrate that, despite significant survey inhomogeneity and high airmass, the catalog exhibits negligible $B$-modes and PSF-related systematics, yielding cosmology-ready measurements with statistical power comparable to DES Y3. Overall, this dataset enables robust, cross-checkable cosmic shear analyses and informs future wide-field surveys in handling inhomogeneous data and PSF performance.

Abstract

We present the Dark Energy Camera All Data Everywhere (DECADE) weak lensing dataset: a catalog of 107 million galaxies observed by the Dark Energy Camera (DECam) in the northern Galactic cap. This catalog was assembled from public DECam data including survey and standard observing programs. These data were consistently processed with the Dark Energy Survey Data Management pipeline as part of the DECADE campaign and serve as the basis of the DECam Local Volume Exploration survey (DELVE) Early Data Release 3 (EDR3). We apply the Metacalibration measurement algorithm to generate and calibrate galaxy shapes. After cuts, the resulting cosmology-ready galaxy shape catalog covers a region of $5,\!412 \,\,{\rm deg}^2$ with an effective number density of $4.59\,\, {\rm arcmin}^{-2}$. The coadd images used to derive this data have a median limiting magnitude of $r = 23.6$, $i = 23.2$, and $z = 22.6$, estimated at ${\rm S/N} = 10$ in a 2 arcsecond aperture. We present a suite of detailed studies to characterize the catalog, measure any residual systematic biases, and verify that the catalog is suitable for cosmology analyses. In parallel, we build an image simulation pipeline to characterize the remaining multiplicative shear bias in this catalog, which we measure to be $m = (-2.454 \pm 0.124) \times10^{-2}$ for the full sample. Despite the significantly inhomogeneous nature of the data set, due to it being an amalgamation of various observing programs, we find the resulting catalog has sufficient quality to yield competitive cosmological constraints.

Figures (15)

• Figure 1: The $i$ band magnitude distribution as a function of different selection cuts applied to derive the final shape catalog. The size of the final sample (black) is approximately 16% the size of the sample with only SourceExtractor and Fitvd cuts (gold).
• Figure 2: Map of the number density of galaxies in our shape catalog. We also show the footprint of three other Stage-III lensing surveys: DES Y3 (grey), KiDS-1000 (dark blue), HSC Y3 (light blue). The dashed lines indicating the Galactic plane with $b = \pm 10\hbox{$^\circ$}$. Our catalog consists of 107 million galaxies covering an area of 5,412 deg$^2$. The distance between our footprint and the Galactic plane is a result of our stellar density mask. This mask is also asymmetric due to the presence of the Galactic bulge.
• Figure 3: Distribution of the limiting magnitude in the $riz$ bands across the footprint for our shape catalog (top) and the DES Y3 catalog (bottom). The median limiting magnitudes, shown as vertical dotted lines, are $r = 23.63 (23.95)$, $i = 23.18 (23.34)$, and $z = 22.59 (22.63)$ for DECADE (DES). The DECADE data has a similar median magnitude as DES Y3, but a considerably wider spread. Around 10% of our area has a higher magnitude limit than the 99% maximum value in DES Y3 (for each band). This map only shows spatial variations in the imaging data quality, and not in the source-galaxy number densities, which is cut at brighter magnitudes and therefore shows less variation (see Figure 1 in paper3).
• Figure 4: Number counts (upper left), shear response $\langle R \rangle$ (upper right), shape noise $\sqrt{\sigma_{e}^2}$ (lower left) and shear weights (lower right) as a function of size ratio $(T/T_{\rm PSF})$ and signal-to-noise (SNR) of the galaxy. For each galaxy in the final shape catalog, a weight is assigned according to the lower right panel. Including this weight enhances the signal-to-noise of any statistic computed with the shape catalog.
• Figure 5: The mean PSF ellipticity error (left, middle) and size error (right) across the DECam focal plane. The large-scale, correlated modes in the ellipticity errors are from interpolation errors in the PSF model and follows those observed in DES Jarvis2020. The size errors show small-scale features that are localized to individual CCDs, and these are "tree rings" arising from impurities in the silicon used in the sensors Estrada:2010:TreeringsPlazas:2014:TreeRingsPlazas:2014:TreeRings2.