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

Pakmor, R ORCID: 0000-0003-3308-2420, Bieri, R ORCID: 0000-0002-4554-4488, Fragkoudi, F ORCID: 0000-0002-0897-3013, Gómez, FA ORCID: 0000-0003-4232-8584, Grand, RJJ ORCID: 0000-0001-9667-1340, Simpson, CM ORCID: 0000-0001-9985-1814, Talbot, RY ORCID: 0000-0001-9393-7879, Van de Voort, F ORCID: 0000-0002-6301-638X and Werhahn, M ORCID: 0000-0003-4984-4389 (2025) Quantifying the intrinsic variability due to randomness of the Auriga galaxy formation model. Monthly Notices of the Royal Astronomical Society, 543 (2). pp. 1761-1774. ISSN 0035-8711

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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, i.e. how much the results change with numerical noise or inherent stochasticity of the physics model. We present a set of seven realizations of high-resolution cosmological zoom-in simulations of a Milky Way-like galaxy with the Auriga galaxy formation model. All realizations 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 disc change by less than 10per cent between the different realizations, 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 2, 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 the first pericentre 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
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press (OUP)
Date of acceptance:	10 September 2025
Date of first compliant Open Access:	6 January 2026
Date Deposited:	06 Jan 2026 15:47
Last Modified:	06 Jan 2026 15:47
DOI or ID number:	10.1093/mnras/staf1542
URI:	https://researchonline.ljmu.ac.uk/id/eprint/27822

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