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Numerical convergence of hydrodynamical simulations of galaxy formation: the abundance and internal structure of galaxies and their cold dark matter haloes

Ludlow, Aaron D; Schaye, Joop; Schaller, Matthieu; Bower, Richard

Numerical convergence of hydrodynamical simulations of galaxy formation: the abundance and internal structure of galaxies and their cold dark matter haloes Thumbnail


Authors

Aaron D Ludlow

Joop Schaye

Matthieu Schaller

Richard Bower



Abstract

We address the issue of numerical convergence in cosmological smoothed particle hydrodynamics simulations using a suite of runs drawn from the EAGLE project. Our simulations adopt subgrid models that produce realistic galaxy populations at a fiducial mass and force resolution, but systematically vary the latter in order to study their impact on galaxy properties. We provide several analytic criteria that help guide the selection of gravitational softening for hydrodynamical simulations, and present results from runs that both adhere to and deviate from them. Unlike dark matter-only simulations, hydrodynamical simulations exhibit a strong sensitivity to gravitational softening, and care must be taken when selecting numerical parameters. Our results–which focus mainly on star formation histories, galaxy stellar mass functions and sizes–illuminate three main considerations. First, softening imposes a minimum resolved escape speed, vε, due to the binding energy between gas particles. Runs that adopt such small softening lengths that vϵ≳10kms−1 (the sound speed in ionised ∼104 K gas) suffer from reduced effects of photo-heating. Second, feedback from stars or active galactic nuclei may suffer from numerical over-cooling if the gravitational softening length is chosen below a critical value, εeFB. Third, we note that small softening lengths exacerbate the segregation of stars and dark matter particles in halo centres, often leading to the counter-intuitive result that galaxy sizes increase as softening is reduced. The structure of dark matter haloes in hydrodynamical runs respond to softening in a way that reflects the sensitivity of their galaxy populations to numerical parameters.

Citation

Ludlow, A. D., Schaye, J., Schaller, M., & Bower, R. (2020). Numerical convergence of hydrodynamical simulations of galaxy formation: the abundance and internal structure of galaxies and their cold dark matter haloes. Monthly Notices of the Royal Astronomical Society, 493(2), 2926-2951. https://doi.org/10.1093/mnras/staa316

Journal Article Type Article
Acceptance Date Jan 29, 2020
Online Publication Date Feb 6, 2020
Publication Date Apr 30, 2020
Deposit Date Feb 6, 2020
Publicly Available Date Mar 10, 2020
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 493
Issue 2
Pages 2926-2951
DOI https://doi.org/10.1093/mnras/staa316

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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.






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