Kavli Affiliate: Eli Rykoff
| First 5 Authors: Robert Armstrong, Erin Sheldon, Eric Huff, Jim Bosch, Eli Rykoff
| Summary:
Upcoming wide field surveys will have many overlapping epochs of the same
region of sky. The conventional wisdom is that in order to reduce the errors
sufficiently for systematics-limited measurements, like weak lensing, we must
do simultaneous fitting of all the epochs. Using current algorithms this will
require a significant amount of computing time and effort. In this paper, we
revisit the potential of using coadds for shear measurements. We show on a set
of image simulations that the multiplicative shear bias can be constrained
below the 0.1% level on coadds, which is sufficient for future lensing surveys.
We see no significant differences between simultaneous fitting and coadded
approaches for two independent shear codes: Metacalibration and BFD. One caveat
of our approach is the assumption of a principled coadd, i.e. the PSF is
mathematically well-defined for all the input images. This requires us to
reject CCD images that do not fully cover the coadd region. We estimate that
the number of epochs that must be rejected for a survey like LSST is on the
order of 20%, resulting in a small loss in depth of less than 0.1 magnitudes.
We also put forward a cell-based coaddition scheme that meets the above
requirements for unbiased weak lensing shear estimation in the context of LSST.
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