Field-level modeling of halo and galaxy alignments
Abstract
We develop an effective field theory (EFT) of intrinsic alignments at the level of spin-2 field fluctuations of large-scale structure tracers, such as the shapes of galaxies and dark matter halos. Our perturbative model includes the non-linear treatment of the Zel'dovich displacement, and contains all necessary shape operators through the third order. We apply our field-level model to the full 3D distribution of galaxy shapes, whose sky projections are a known contaminant of cosmic shear measurements. Our field-level EFT model achieves a better description of the helicity fields of dark matter halo shapes than the standard non-linear alignment (NLA) and tidal torquing + tidal alignment (TATT) models in the literature, as evidenced by improved correlations with the simulations' initial conditions. We perform precision measurements of field-level bias parameters by means of a generalized least-squares problem, for which we derive an optimal estimator and analytic covariance matrices. We measure the full set of linear, quadratic, and cubic shape bias coefficients as a function of halo mass in the Quijote N-body simulations. We then study the intrinsic alignments of galaxies in the FLAMINGO hydrodynamical simulation, focusing on observationally relevant samples: spirals, ellipticals, luminous red galaxies (LRG) and emission-line galaxies (ELG). We detect linear and nonlinear alignment coefficients at high significance for LRG, spiral and elliptical galaxies. We also find evidence for non-zero density-weighted tidal bias coefficient of the simulated ELG. This work supports the notion that EFT-based models of alignments will be paramount in optimally extracting constraints from future shape correlations, and lays the foundation for the development of simulation-based priors for future galaxy shape samples.
Related
- Constraints on the magnetic field in the hadronic scenario for the origin of the radio halo in the A1795 galaxy cluster
- LMC-induced Perturbations in the Milky Way Halo II: Bridging Field-level Inference and Summary-level Simulation-Based Inference
- Inductive Biases in Field-Level Cosmological Inference from Galaxy Catalogs
- Model-Independent Assessments of Tidal Alignment and Density-Weighting Dependence in Galaxy Intrinsic Alignments
- Inductive Biases in Field-level Cosmological Inference from Galaxy Catalogs
BibTeX
@misc{kokron2026fieldlevel,
title = {{Field-level modeling of halo and galaxy alignments}},
author = {Nickolas Kokron and Mikhail M. Ivanov and James M. Sullivan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.36027},
eprint = {2610.36027},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.36027},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Field-level modeling of halo and galaxy alignments
AU - Nickolas Kokron
AU - Mikhail M. Ivanov
AU - James M. Sullivan
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.36027
UR - https://arxiv.org/abs/2610.36027
AB - We develop an effective field theory (EFT) of intrinsic alignments at the level of spin-2 field fluctuations of large-scale structure tracers, such as the shapes of galaxies and dark matter halos. Our perturbative model includes the non-linear treatment of the Zel'dovich displacement, and contains all necessary shape operators through the third order. We apply our field-level model to the full 3D distribution of galaxy shapes, whose sky projections are a known contaminant of cosmic shear measurements. Our field-level EFT model achieves a better description of the helicity fields of dark matter halo shapes than the standard non-linear alignment (NLA) and tidal torquing + tidal alignment (TATT) models in the literature, as evidenced by improved correlations with the simulations' initial conditions. We perform precision measurements of field-level bias parameters by means of a generalized least-squares problem, for which we derive an optimal estimator and analytic covariance matrices. We measure the full set of linear, quadratic, and cubic shape bias coefficients as a function of halo mass in the Quijote N-body simulations. We then study the intrinsic alignments of galaxies in the FLAMINGO hydrodynamical simulation, focusing on observationally relevant samples: spirals, ellipticals, luminous red galaxies (LRG) and emission-line galaxies (ELG). We detect linear and nonlinear alignment coefficients at high significance for LRG, spiral and elliptical galaxies. We also find evidence for non-zero density-weighted tidal bias coefficient of the simulated ELG. This work supports the notion that EFT-based models of alignments will be paramount in optimally extracting constraints from future shape correlations, and lays the foundation for the development of simulation-based priors for future galaxy shape samples.
ER -