Abstract
ABSTRACT We introduce a new software package for modelling the point spread function (PSF) of astronomical images, called piff (PSFs In the Full FOV), which we apply to the first three years (known as Y3) of the Dark Energy Survey (DES) data. We describe the relevant details about the algorithms used by piff to model the PSF, including how the PSF model varies across the field of view (FOV). Diagnostic results show that the systematic errors from the PSF modelling are very small over the range of scales that are important for the DES Y3 weak lensing analysis. In particular, the systematic errors from the PSF modelling are significantly smaller than the corresponding results from the DES year one (Y1) analysis. We also briefly describe some planned improvements to piff that we expect to further reduce the modelling errors in future analyses.
Highlights
The Dark Energy Survey (DES, DES Collaboration 2016) has already produced very precise constraints on cosmology (Abbott et al 2018) using just the first year of data (Y1)
We have presented a new software package for point spread function (PSF) estimation of astronomical images, called PIFF, which was developed primarily for the DES Y3 weak lensing (WL) analysis
The PIFF PSF models were tested on the Y3 data and show significantly smaller residuals than had been seen in the Y1 data
Summary
The Dark Energy Survey (DES, DES Collaboration 2016) has already produced very precise constraints on cosmology (Abbott et al 2018) using just the first year of data (Y1). The Y1 weak lensing (WL) cosmic shear measurements alone were able to constrain the combination σ 8( m/0.3)0.5 to 3.5 per cent uncertainty (Troxel et al 2018). Such precise constraints require that systematic uncertainties be controlled to levels smaller than the statistical uncertainties. One of the most significant systematic uncertainties in the DES Y1 cosmic shear analysis was the estimation of the point spread function (PSF) at the location of each galaxy. The basis used was the pixel values on a grid The coefficients of this model are interpolated using a polynomial in the chip coordinates, x and y, across the area of each CCD image. Detailed instructions for using PIFF can be found in the online code documentation.
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