Photometric redshifts and intrinsic alignments: degeneracies and biases in 3×2pt analysis
arxiv(2024)
摘要
We present a systematic study of cosmological parameter bias in weak lensing
and large-scale structure analyses for upcoming imaging surveys induced by the
interplay of intrinsic alignments (IA) and photometric redshift (photo-z) model
mis-specification error. We first examine the degeneracies between the
parameters of the Tidal Alignment - Tidal Torquing (TATT) model for IA and of a
photo-z model including a mean shift (Δz̅) and variance
(σ_z) for each tomographic bin of lenses and sources, under a variety
of underlying true IA behaviors. We identify strong degeneracies between: (1)
the redshift scaling of the tidal alignment amplitude and the mean shift and
variances of source bins, (2) the redshift scaling of the tidal torquing
amplitude and the variance of the lowest-z source bin, and (3) the IA source
density weighting and the mean shift and variance of several source bins. We
then use this information to guide our exploration of the level of cosmological
parameter bias which can be induced given incorrect modelling of IA, photo-z,
or both. We find that marginalizing over all the parameters of TATT is
generally sufficient to preclude cosmological parameter bias in the scenarios
we consider. However, this does not necessarily mean that IA and photo-z
parameters are themselves unbiased, nor does it mean that the best-fit model is
a good fit to the data. We also find scenarios where the inferred parameters
produce χ^2_ DOF values indicative of a good fit but cosmological
parameter bias is significant, particularly when the IA source density
weighting parameter is not marginalized over.
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