Statistics of the projected angles between the black-hole spin and the host-galaxy rotation axes from NewHorizon

¹ ILANCE, CNRS – University of Tokyo International Research Laboratory Kashiwa Chiba 277-8582, Japan
² Kavli IPMU (WPI), UTIAS, The University of Tokyo Kashiwa Chiba 277-8583, Japan
³ Department of Physics, School of Science, The University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-0033, Japan
⁴ Research Institute, Kochi University of Technology Tosa Yamada Kochi 782-8502, Japan
⁵ Co-creation Organization of Regional Innovation, Kochi University of Technology Tosa Yamada Kochi 782-8502, Japan
⁶ Institut d’Astrophysique de Paris, CNRS and Sorbonne Université, UMR 7095 98 bis Boulevard Arago F-75014 Paris, France
⁷ Institute of Astronomy and Astrophysics, Academia Sinica, No. 1, Section 4 Roosevelt Road Taipei 10617, Taiwan
⁸ Department of Astronomy and Yonsei University Observatory, Yonsei University Seoul 03722, Republic of Korea

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 10 September 2025
Accepted: 4 December 2025

Abstract

Understanding the alignment between active galactic nucleus (AGN) jets and their host galaxies is crucial for interpreting AGN unification models, jet feedback processes, and the coevolution of galaxies and their central black holes (BHs). In this study, we use the high-resolution cosmological zoom-in simulation NEWHORIZON, which self-consistently evolves BH mass and spin, to statistically examine the relationship between AGN jet orientation and host galaxy structure. Building upon our previous work, we extend the analysis of projected (2D) alignment angles to facilitate more direct comparisons with recent observational studies. In our methodology, galaxy orientations are estimated using optical position angles derived from synthetic DESI-LS and Euclid images, while BH spin vectors serve as proxies for AGN jet directions. From a carefully selected sample of 100 BH–galaxy systems at low redshift, we generate a catalog of 5000 mock optical images using a Monte Carlo approach that samples random viewing angles and redshifts. Our results reveal a statistically significant tendency for AGN jets to align with the orientation of their host galaxies, consistent with recent observations combining very long baseline interferometry (VLBI) and optical imaging of nearby AGNs. Furthermore, we find a slightly stronger alignment when using kinematic position angles derived from synthetic MaNGA-like stellar velocity fields. These findings underscore the importance of combining morphological, kinematic, and polarimetric information to disentangle the complex interplay between BH spin evolution, accretion mode, and the galactic environment in shaping the direction of relativistic jets.