Euclid preparation. Testing analytic models of galaxy intrinsic alignments in the Euclid Flagship simulation
Abstract
We model intrinsic alignments (IA) in Euclid's Flagship simulation to investigate its impact on Euclid's weak lensing signal. Our IA implementation in the Flagship simulation takes into account photometric properties of galaxies as well as their dark matter host halos. We compare simulations against theory predictions, determining the parameters of two of the most widely used IA models: the Non Linear Alignment (NLA) and the Tidal Alignment and Tidal Torquing (TATT) models. We measure the amplitude of the simulated IA signal as a function of galaxy magnitude and colour in the redshift range . We find that both NLA and TATT can accurately describe the IA signal in the simulation down to scales of -Mpc. We measure alignment amplitudes for red galaxies comparable to those of the observations, with samples not used in the calibration procedure. For blue galaxies, our constraints are consistent with zero alignments in our first redshift bin , but we detect a non-negligible signal at higher redshift, which is, however, consistent with the upper limits set by observational constraints. Additionally, several hydrodynamical simulations predict alignment for spiral galaxies, in agreement with our findings. Finally, the evolution of alignment with redshift is realistic and comparable to that determined in the observations. However, we find that the commonly adopted redshift power-law for IA fails to reproduce the simulation alignments above . A significantly better agreement is obtained when a luminosity dependence is included, capturing the intrinsic luminosity evolution with redshift in magnitude-limited surveys. We conclude that the Flagship IA simulation is a useful tool for translating current IA constraints into predictions for IA contamination of Euclid-like samples.
Cite
@article{arxiv.2601.07784,
title = {Euclid preparation. Testing analytic models of galaxy intrinsic alignments in the Euclid Flagship simulation},
author = {Euclid Collaboration and R. Paviot and B. Joachimi and K. Hoffmann and S. Codis and I. Tutusaus and D. Navarro-Gironés and J. Blazek and F. Hervas-Peters and B. Altieri and S. Andreon and N. Auricchio and C. Baccigalupi and M. Baldi and S. Bardelli and A. Biviano and E. Branchini and M. Brescia and S. Camera and G. Cañas-Herrera and V. Capobianco and C. Carbone and V. F. Cardone and J. Carretero and S. Casas and F. J. Castander 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 F. Courbin and H. M. Courtois and A. Da Silva and H. Degaudenzi and S. de la Torre and G. De Lucia and H. Dole and F. Dubath and C. A. J. Duncan and X. Dupac and S. Dusini and S. Escoffier and M. Farina and R. Farinelli and S. Farrens and S. Ferriol and F. Finelli and P. Fosalba and M. Frailis and E. Franceschi 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 K. Jahnke and M. Jhabvala and E. Keihänen and S. Kermiche and A. Kiessling and M. Kilbinger and B. Kubik and M. Kümmel and M. Kunz and H. Kurki-Suonio 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 S. Maurogordato 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 C. Neissner and S. -M. Niemi and C. Padilla and S. Paltani 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 R. Rebolo 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 E. Sefusatti and G. Seidel and S. Serrano and P. Simon and C. Sirignano and G. Sirri and A. Spurio Mancini 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 L. Valenziano and J. Valiviita and T. Vassallo and G. Verdoes Kleijn and A. Veropalumbo and Y. Wang and J. Weller and A. Zacchei and G. Zamorani and F. M. Zerbi and E. Zucca and E. Bozzo and C. Burigana and R. Cabanac and M. Calabrese and J. A. Escartin Vigo and L. Gabarra and W. G. Hartley and S. Matthew and M. Maturi and N. Mauri and R. B. Metcalf and A. Pezzotta and M. Pöntinen and C. Porciani and I. Risso and V. Scottez and M. Sereno and M. Tenti and M. Viel and M. Wiesmann and Y. Akrami and I. T. Andika and S. Anselmi and M. Archidiacono and F. Atrio-Barandela and D. Bertacca and M. Bethermin and A. Blanchard and L. Blot and H. Böhringer and M. Bonici and S. Borgani and M. L. Brown and S. Bruton and A. Calabro and B. Camacho Quevedo and F. Caro and C. S. Carvalho and T. Castro and F. Cogato and S. Conseil and A. R. Cooray and O. Cucciati and S. Davini and F. De Paolis and G. Desprez and A. Díaz-Sánchez and J. J. Diaz and S. Di Domizio and J. M. Diego and P. Dimauro and M. Y. Elkhashab and A. Enia and Y. Fang and A. G. Ferrari and A. Finoguenov and A. Fontana and A. Franco and K. Ganga and J. García-Bellido and T. Gasparetto and V. Gautard and R. Gavazzi and E. Gaztanaga and F. Giacomini and F. Gianotti and G. Gozaliasl and M. Guidi and C. M. Gutierrez and A. Hall and S. Hemmati and H. Hildebrandt and J. Hjorth and S. Joudaki and J. J. E. Kajava and Y. Kang and V. Kansal and D. Karagiannis and K. Kiiveri and J. Kim and C. C. Kirkpatrick and S. Kruk and J. Le Graet and L. Legrand and M. Lembo and F. Lepori and G. Leroy and G. F. Lesci and J. Lesgourgues and T. I. Liaudat and A. Loureiro and J. Macias-Perez and G. Maggio and M. Magliocchetti and F. Mannucci and R. Maoli and C. J. A. P. Martins and L. Maurin and M. Miluzio and P. Monaco and C. Moretti and G. Morgante and S. Nadathur and K. Naidoo and P. Natoli and A. Navarro-Alsina and S. Nesseris and L. Pagano and D. Paoletti and F. Passalacqua and K. Paterson and L. Patrizii and A. Pisani and D. Potter and S. Quai and M. Radovich and S. Sacquegna and M. Sahlén and D. B. Sanders and E. Sarpa and A. Schneider and M. Schultheis and D. Sciotti and E. Sellentin and L. C. Smith and J. G. Sorce and K. Tanidis and C. Tao and G. Testera and R. Teyssier and S. Tosi and A. Troja and M. Tucci and C. Valieri and A. Venhola and D. Vergani and F. Vernizzi and G. Verza and P. Vielzeuf and N. A. Walton},
journal= {arXiv preprint arXiv:2601.07784},
year = {2026}
}