Euclid. Optimising tomographic redshift binning for 3 × 2 pt power spectrum constraints on dark energy

The tomographic approach to analysing the 3 × 2 pt signal involves dividing the observed galaxy sample into a configuration of redshift bins. We present a simulation-based method to explore the optimum tomographic binning strategy for Euclid , focussing on the expected configuration of its first major data release (DR1). To do so, we 1) simulated a Euclid -like observation and generated mock shear catalogues from multiple realisations of the 3 × 2 pt fields on the sky; and 2) measured the 3 × 2 pt Pseudo- C ℓ power spectra for a given tomographic configuration and derived the constraints they place on the standard dark energy equation-of-state parameters, ( w 0 , w a ). For a simulation including Gaussian-distributed photometric redshift uncertainties and shape noise under a ΛCDM cosmology, we find that bins that are equipopulated with galaxies yield the best constraints on ( w 0 , w a ) for an analysis of the full 3 × 2 pt signal or the angular clustering component only. For the cosmic shear component, the optimum ( w 0 , w a ) constraints can be achieved by bins equally spaced in fiducial comoving distance. However, the advantage with respect to alternative binning choices is only of a few per cent in the size of the 1 σ ( w 0 , w a ) contour and we conclude that the cosmic shear is relatively insensitive to the binning methodology. We find that the information gain extracted on ( w 0 , w a ) for any 3 × 2 pt component starts to become saturated beyond roughly seven or eight bins. Any marginal gains resulting from a greater number of bins are likely to be limited by additional uncertainties present in a real measurement and the increasing demand for accuracy of the covariance matrix. Finally, we considered a 5% contamination from catastrophic photometric redshift outliers and found that if these errors are not mitigated in the analysis, the bias induced in the 3 × 2 pt signal for ten equipopulated bins results in dark energy constraints that are inconsistent with the fiducial ΛCDM cosmology at ≳3 σ .

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520 - Astronomie, Kartografie

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0004-6361
1432-0746

Language

English

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Yes

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Published

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peer-reviewed

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Gold

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Citation

Wong, J. H. W., Brown, M. L., Duncan, C. A. J., Amara, A., Andreon, S., Baccigalupi, C., Baldi, M., Bardelli, S., Bonino, D., Branchini, E., Brescia, M., Brinchmann, J., Caillat, A., Camera, S., Capobianco, V., Carbone, C., Carretero, J., Casas, S., Castellano, M., et al. (2026). Euclid. Optimising tomographic redshift binning for 3 × 2 pt power spectrum constraints on dark energy. Astronomy & Astrophysics, 708, A284. https://doi.org/10.1051/0004-6361/202553742

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