Euclid: Improving redshift distribution reconstruction using a deep-to-wide transfer function
Abstract
The Euclid mission seeks to understand the Universe expansion history and the nature of dark energy, which requires a very accurate estimate of redshift distribution. Achieving this accuracy relies on reference samples with spectroscopic redshifts, together with a procedure to match them to survey sources for which only photometric redshifts are available. One important source of systematic uncertainty is the mismatch in photometric properties between galaxies in the Euclid survey and the reference objects. We develop a method to degrade the photometry of objects with deep photometry to match the properties of any shallower survey in the multi-band photometric space, preserving all the correlations between the fluxes and their uncertainties. We compare our transfer method with more demanding image-based methods, such as Balrog from the Dark Energy Survey Collaboration. According to metrics, our method outperforms Balrog. We implement it in the redshift distribution reconstruction, based on the self-organising map approach of arXiv:1509.03318, and test it using a realistic sample from the Euclid Flagship Simulation. We find that the key ingredient is to ensure that the reference objects are distributed in the colour space the same way as the wide-survey objects, which can be efficiently achieved with our transfer method. In our best implementation, the mean redshift biases are consistently reduced across the tomographic bins, bringing a significant fraction of them within the Euclid accuracy requirements in all tomographic bins. Equally importantly, the tests allow us to pinpoint which step in the calibration pipeline has the strongest impact on achieving the required accuracy. Our approach also reproduces the overall redshift distributions, which are crucial for applications such as angular clustering.
Cite
@article{arxiv.2601.02005,
title = {Euclid: Improving redshift distribution reconstruction using a deep-to-wide transfer function},
author = {Y. Kang and S. Paltani and W. G. Hartley and M. Bolzonella and A. H. Wright and F. Dubath and F. J. Castander and D. C. Masters and W. d'Assignies and H. Hildebrandt and O. Ilbert and M. Manera and W. Roster and S. A. Stanford and N. Aghanim and B. Altieri and S. Andreon and N. Auricchio and H. Aussel and C. Baccigalupi and M. Baldi and S. Bardelli and P. Battaglia and A. Biviano and E. Branchini and M. Brescia and J. Brinchmann and S. Camera and G. Cañas-Herrera and V. Capobianco and C. Carbone and V. F. Cardone and J. Carretero and S. Casas and M. Castellano and G. Castignani and S. Cavuoti and K. C. Chambers and A. Cimatti and C. Colodro-Conde and G. Congedo and L. Conversi and Y. Copin and A. Costille and F. Courbin and H. M. Courtois and M. Cropper and H. Degaudenzi and G. De Lucia and H. Dole and C. A. J. Duncan and X. Dupac and S. Dusini and A. Ealet and S. Escoffier and M. Farina and R. Farinelli and S. Farrens and F. Faustini and S. Ferriol and F. Finelli and N. Fourmanoit and M. Frailis and E. Franceschi and M. Fumana and S. Galeotta and K. George and B. Gillis and C. Giocoli and J. Gracia-Carpio and A. Grazian and F. Grupp and S. V. H. Haugan and H. Hoekstra and W. Holmes and F. Hormuth and A. Hornstrup and P. Hudelot and K. Jahnke and M. Jhabvala and B. Joachimi and E. Keihänen and S. Kermiche and A. Kiessling and B. Kubik and M. Kümmel and M. Kunz and H. Kurki-Suonio and R. Laureijs and A. M. C. Le Brun and S. Ligori and P. B. Lilje and V. Lindholm and I. Lloro and G. Mainetti and D. Maino and E. Maiorano and O. Mansutti and S. Marcin and O. Marggraf and M. Martinelli and N. Martinet and F. Marulli and R. J. Massey and E. Medinaceli and S. Mei and Y. Mellier and M. Meneghetti and E. Merlin and G. Meylan and A. Mora and M. Moresco and L. Moscardini and R. Nakajima and C. Neissner and S. -M. Niemi and C. Padilla and F. Pasian and K. Pedersen and V. Pettorino and S. Pires and G. Polenta and M. Poncet and L. A. Popa and L. Pozzetti and F. Raison and A. Renzi and J. Rhodes and G. Riccio and E. Romelli and M. Roncarelli and R. Saglia and Z. Sakr and A. G. Sánchez and D. Sapone and B. Sartoris and P. Schneider and T. Schrabback and A. Secroun and G. Seidel and S. Serrano and P. Simon and C. Sirignano and G. Sirri and L. Stanco and J. Steinwagner and P. Tallada-Crespí and A. N. Taylor and I. Tereno and N. Tessore and S. Toft and R. Toledo-Moreo and F. Torradeflot and I. Tutusaus and J. Valiviita and T. Vassallo and A. Veropalumbo and Y. Wang and J. Weller and G. Zamorani and F. M. Zerbi and I. A. Zinchenko and E. Zucca and J. García-Bellido and J. Martín-Fleitas and V. Scottez and M. Viel and R. Teyssier},
journal= {arXiv preprint arXiv:2601.02005},
year = {2026}
}