Quantifying the intrinsic variability due to randomness of the Auriga galaxy formation model

Pakmor, Rüdiger, Bieri, Rebekka, Fragkoudi, Francesca, Gómez, Facundo A, Grand, Robert J J, Simpson, Christine M, Talbot, Rosie Y, van de Voort, Freeke ORCID: https://orcid.org/0000-0002-6301-638X and Werhahn, Maria 2025. Quantifying the intrinsic variability due to randomness of the Auriga galaxy formation model. Monthly Notices of the Royal Astronomical Society , staf1542. 10.1093/mnras/staf1542

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Abstract

Numerical simulations have become an indispensable tool in astrophysics. To interpret their results, it is critical to understand their intrinsic variability, that is, how much the results change with numerical noise or inherent stochasticity of the physics model. We present a set of seven realisations of high-resolution cosmological zoom-in simulations of a Milky Way-like galaxy with the Auriga galaxy formation model. All realisations share the same initial conditions and code parameters, but draw different random numbers for the inherently stochastic parts of the model. We show that global galaxy properties at z = 0, including stellar mass, star formation history, masses of stellar bulge and stellar disc, the radius and height of the stellar disk change by less than 10% between the different realisations, and that magnetic field structures in the disc and the halo are very similar. In contrast, the star formation rate today can vary by a factor of two and the internal morphological structure of the stellar disc can change. The time and orbit of satellite galaxies and their galaxy properties when falling into the main halo are again very similar, but their orbits start to deviate after first pericenter passage. Finally, we show that changing the mass resolution of all matter components by a factor of 8 in the Auriga model changes galaxy properties significantly more than the intrinsic variability of the model, and that these changes are systematic. This limits detailed comparisons between simulations at different numerical resolutions.

Item Type:	Article
Date Type:	Published Online
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	License information from Publisher: LICENSE 1: URL: https://creativecommons.org/licenses/by/4.0/, Start Date: 2025-09-13
Publisher:	Oxford University Press
ISSN:	0035-8711
Last Modified:	29 Sep 2025 12:00
URI:	https://orca.cardiff.ac.uk/id/eprint/181388

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