Abstract
Abstract Galaxy color gradients (CGs)—i.e., spectral energy distributions that vary across the galaxy profile—will impact galaxy shape measurements when the modeled point-spread function (PSF) corresponds to that for a galaxy with spatially uniform color. This paper describes the techniques and results of a study of the expected impact of galaxy CGs on weak lensing measurements with the Large Synoptic Survey Telescope (LSST) when the PSF size depends on wavelength. The bias on cosmic shear measurements from CGs is computed both for parametric bulge+disk galaxy simulations and for more realistic chromatic galaxy surface brightness profiles based on Hubble Space Telescope V- and I-band images in the All-Wavelength Extended Groth Strip International Survey (AEGIS). For the parametric galaxies, and for the more realistic galaxies derived from AEGIS galaxies with a sufficient signal-to-noise ratio that CG bias can be isolated, the predicted multiplicative shear biases due to CGs are found to be at least a factor of two below the LSST full-depth requirement on the total systematic uncertainty in the redshift-dependent shear calibration. The analysis code and data products are publicly available (https://github.com/sowmyakth/measure_cg_bias).
Highlights
Weak gravitational lensing produces coherent alignment of images of distant galaxies due to the intervening tidal gravitational field (Bartelmann & Schneider 2001)
This paper describes the techniques and results of a study of the expected impact of galaxy color gradients on weak lensing measurements with the Large Synoptic Survey Telescope (LSST) when the point spread function (PSF) size depends on wavelength
The bias on cosmic shear measurements from color gradients is computed both for parametric bulge+disk galaxy simulations and for more realistic chromatic galaxy surface brightness profiles based on Hubble Space Telescope (HST) V- and I-band images in the All-wavelength Extended Groth strip International Survey (AEGIS) survey
Summary
Weak gravitational lensing produces coherent alignment of images of distant galaxies due to the intervening tidal gravitational field (Bartelmann & Schneider 2001). The effects of chromatic atmospheric PSFs on weak lensing measurements have been studied by Meyers & Burchat (2015) who conclude that while the predicted shear bias is significant compared to the LSST requirements, the bias can be reduced sufficiently to meet the LSST requirements if the PSF is corrected using multi-band photometry and machine learning techniques. These corrections are based on the assumption that the spatial and wavelength dependencies of the galaxy surface brightness profile are separable. It is necessary to quantify the size of this bias compared to the LSST requirements on bias for shear estimators
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