Modeling gravitational wave sources in the MillenniumTNG simulations

¹ Dipartimento di Fisica e Astronomia “Augusto Righi”, Università di Bologna Via Piero Gobetti 93/2 I-40129 Bologna, Italy
² INAF, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna Via Piero Gobetti 93/3 I-40129 Bologna, Italy
³ INFN, Sezione di Bologna Viale Berti Pichat 6/2 I-40127 Bologna, Italy
⁴ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB) c. Martí i Franquès 1 08028 Barcelona, Spain
⁵ Universidad Andres Bello, Facultad de Ciencias Exactas, Departamento de Fisica y Astronomia, Instituto de Astrofisica Fernandez Concha 700 Las Condes Santiago RM, Chile
⁶ Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik Albert Ueberle Str. 2 D-69120 Heidelberg, Germany
⁷ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen D-69120 Heidelberg, Germany
⁸ Max-Planck-Institut für Astrophysik Karl-Schwarzschild-Strasse 1 D-85748 Garching, Germany
⁹ Institute for Computational Cosmology, Department of Physics, Durham University South Road Durham DH13LE, UK
¹⁰ Center for Astrophysics | Harvard & Smithsonian 60 Garden St Cambridge MA 02138, USA

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Received: 6 October 2025
Accepted: 9 January 2026

Abstract

We introduce a flexible framework for building gravitational wave (GW) event catalogs in hydrodynamic simulations of galaxy formation. Our framework couples the state-of-the-art binary population synthesis code SEVN with AREPO-GW – a module fully integrated into the moving-mesh code AREPO – to assign merger events of binary compact objects to stellar particles in simulations by stochastically sampling merger tables generated with SEVN. AREPO-GW supports both on-the-fly operation, producing event catalogs during simulations, and post-processing, using snapshots from existing runs. The algorithm is fully parallel and can be readily adapted to outputs from simulation codes beyond AREPO. To demonstrate the capabilities of our new framework, we applied AREPO-GW in post-processing to simulations from the MillenniumTNG suite, including its flagship box – one of the largest full-physics cosmological simulations to date. We investigate key properties of the resulting GW event catalog, built on SEVN predictions, focusing on comoving merger rates, formation efficiencies, delay-time distributions, and progenitor mass and metallicity distributions. We also examine how these properties vary with simulated volume. We find that GW progenitor rates closely track simulated star formation histories and are generally consistent with current observational constraints at low redshift, aside from an excess – by a factor of ∼4.5 – in binary black hole mergers, in line with trends reported in the literature. Moreover, our binary black hole merger rates decline more slowly with redshift than current observational estimates for z ≲ 1. Finally, the analysis of progenitor mass functions across different formation channels reveals only mild redshift evolution, in agreement with earlier studies, while the binary black hole mass function displays features compatible with current observational determinations. These findings highlight the potential of our novel framework to enable detailed predictions for upcoming GW surveys within a full cosmological context.