Combining cosmic shear data with correlated photo-$z$ uncertainties: constraints from DESY1 and HSC-DR1

Understand

An accurate calibration of the source redshift distribution $p(z)$ is a key aspect in the analysis of cosmic shear data.

• This, one way or another, requires the use of spectroscopic or high-quality photometric samples.
• However, the difficulty to obtain colour-complete spectroscopic samples matching the depth of weak lensing catalogs means that the analyses of different cosmic shear datasets often use the same samples for redshift calibration.
• This introduces a source of statistical and systematic uncertainty that is highly correlated across different weak lensing datasets, and which must be accurately characterised and propagated in order to obtain robust cosmological constraints from their combination.