Galaxy–Galaxy lensing in HSC: Validation tests and the impact of heterogeneous spectroscopic training sets. Issue 4 (26th October 2019) - Speagle, Joshua S
ABSTRACT: Although photometric redshifts (photo- z 's) are crucial ingredients for current and upcoming large-scale surveys, the high-quality spectroscopic redshifts currently available to train, validate, and test them are substantially non-representative in both magnitude and colour. We investigate the nature and structure of this bias by tracking how objects from a heterogeneous training sample contribute to photo- z predictions as a function of magnitude and colour, and illustrate that the underlying redshift distribution at fixed colour can evolve strongly as a function of magnitude. We then test the robustness of the galaxy–galaxy lensing signal in 120 deg 2 of HSC–SSP DR1 data to spectroscopic completeness and photo- z biases, and find that their impacts are sub-dominant to current statistical uncertainties. Our methodology provides a framework to investigate how spectroscopic incompleteness can impact photo- z -based weak lensing predictions in future surveys such as LSST and WFIRST .