Hydrodynamical structure formation in Milgromian cosmology
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We present the first hydrodynamical cosmological simulations in the νHDM framework based on Milgromian dynamics (MOND) with light (11 eV) sterile neutrinos. νHDM can explain the expansion history, CMB anisotropies, and galaxy cluster dynamics similarly to standard cosmology while preserving MOND’s successes on galaxy scales, making this the most conservative Milgromian framework. We generate initial conditions including sterile neutrinos using CAMB and MUSIC and modify the publicly available code PHANTOM OF RAMSES to run νHDM models. The simulations start at redshift ze = 199, when the gravitational fields are stronger than a0 provided this does not vary. We analyse the growth of structure and investigate the impact of resolution and box size, which is at most 600 comoving Mpc. Large density contrasts arise at late times, which may explain the KBC void and Hubble tension. We quantify the mass function of formed structures at different redshifts. We show that the sterile neutrino mass fraction in these structures is similar to the cosmic fraction at high masses (consistent with MOND dynamical analyses) but approaches zero at lower masses, as expected for galaxies. We also identify structures with a low peculiar velocity comparable to the Local Group, but these are rare. The onset of group/cluster-scale structure formation at ze ≈ 4 appears to be in tension with observations of high redshift galaxies, which we discuss in comparison to prior analytical work in a MONDian framework. The formation of a cosmic web of filaments and voids demonstrates that this is not unique to standard Einstein/Newton-based cosmology.
Wittenburg , N , Kroupa , P , Banik , I , Candlish , G & Samaras , N 2023 , ' Hydrodynamical structure formation in Milgromian cosmology ' , Monthly Notices of the Royal Astronomical Society , vol. 523 , no. 1 , pp. 453–473 . https://doi.org/10.1093/mnras/stad1371
Monthly Notices of the Royal Astronomical Society
Copyright © 2023 The Author(s). Published by Oxford University Press on behalf of the Royal Society. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the final published version of the work, which was originally published at https://doi.org/10.1093/mnras/stad1371.
DescriptionIB is supported by Science and Technology Facilities Council grant ST/V000861/1. He acknowledges support from a “Pathways to Research” fellowship from the University of Bonn in 2021 after an Alexander von Humboldt Foundation postdoctoral research fellowship (2018 − 2020). We thank the Deutscher Akademischer Austauschdienst-Eastern European exchange program at the University of Bonn for supporting the Bonn-Prague exchange. We acknowledge financial support through the transdisciplinary research area TRA-Matter at the University of Bonn.
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