Propagating sample variance uncertainties in redshift calibration: simulations, theory and application to the COSMOS2015 data

Understand

Cosmological analyses of galaxy surveys rely on knowledge of the redshift distribution of their galaxy sample.

• This is usually derived from a spectroscopic and/or many-band photometric calibrator survey of a small patch of sky.
• The uncertainties in the redshift distribution of the calibrator sample include a contribution from shot noise, or Poisson sampling errors, but, given the small volume they probe, they are dominated by sample variance introduced by large-scale structures.
• Redshift uncertainties have been shown to constitute one of the leading contributions to systematic uncertainties in cosmological inferences from weak lensing and galaxy clustering, and hence they must be propagated through the analyses.