Testing the effect of resolution on gravitational fragmentation with Lagrangian hydrodynamic schemes

Yamamoto, Yasuyoshi; Okamoto, Takashi; Saitoh, Takayuki R.

doi:10.1093/mnras/stab1095

Cited by 4 publications

(1 citation statement)

References 26 publications

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“…Mac Low et al 1998;Meru & Bate 2011;Joos et al 2013;Bate et al 2014;Hosokawa et al 2016;Haugbølle et al 2018;Meyer et al 2018;Hennebelle 2018), and a few have shown that convergence has been reached (e.g. Commerc ¸on et al 2008;Meru & Bate 2012;Lee & Hennebelle 2018a,b;Yamamoto et al 2021) 1 . Although convergence studies are required to produce robust conclusions, this is not always possible.…”

Section: Introductionmentioning

confidence: 99%

On the origin of magnetic fields in stars – II. The effect of numerical resolution

Wurster

Bate

Price

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Are the kG-strength magnetic fields observed in young stars a fossil field left over from their formation or are they generated by a dynamo? Our previous numerical study concluded that magnetic fields must originate by a dynamo process. Here, we continue that investigation by performing even higher numerical resolution calculations of the gravitational collapse of a 1 M⊙ rotating, magnetised molecular cloud core through the first and second collapse phases until stellar densities are reached. Each model includes Ohmic resistivity, ambipolar diffusion, and the Hall effect. We test six numerical resolutions, using between 105 and 3 × 107 particles to model the cloud. At all but the lowest resolutions, magnetic walls form in the outer parts of the first hydrostatic core, with the maximum magnetic field strength located within the wall rather than at the centre of the core. At high resolution, this magnetic wall is disrupted by the Hall effect, producing a magnetic field with a spiral-shaped distribution of intensity. As the second collapse occurs, this field is dragged inward and grows in strength, with the maximum field strength increasing with resolution. As the second core forms, the maximum field strength exceeds 1 kG in our highest resolution simulations, and the stellar core field strength exceeds this threshold at the highest resolution. Our resolution study suggests that kG-strength magnetic fields may be implanted in low-mass stars during their formation, and may persist over long timescales given that the diffusion timescale for the magnetic field exceeds the age of the Universe.

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Section: Introductionmentioning

confidence: 99%

On the origin of magnetic fields in stars – II. The effect of numerical resolution

Wurster

Bate

Price

et al. 2022

Monthly Notices of the Royal Astronomical Society

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The impact of cosmic rays on dynamical balance and disc–halo interaction in L⋆ disc galaxies

Chan¹,

Kereš²,

Gurvich³

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Cosmic rays (CRs) are an important component in the interstellar medium (ISM), but their effect on the dynamics of the disk-halo interface (< 10 kpc from the disk) is still unclear. We study the influence of CRs on the gas above the disk with high-resolution FIRE-2 cosmological simulations of late-type L⋆ galaxies at redshift z ∼ 0. We compare runs with and without CR feedback (with constant anisotropic diffusion κ∥ ∼ 3 × 1029cm2/s and streaming). Our simulations capture the relevant disk halo interactions, including outflows, inflows, and galactic fountains. Extra-planar gas in all of the runs satisfies dynamical balance, where total pressure balances the weight of the overlying gas. While the kinetic pressure from non-uniform motion (≳ 1 kpc scale) dominates in the midplane, thermal and bulk pressures (or CR pressure if included) take over at large heights. We find that with CR feedback, (1) the warm (∼104 K) gas is slowly accelerated by CRs; (2) the hot (>5 × 105 K) gas scale height is suppressed; (3) the warm-hot (2 × 104 − 5 × 105 K) medium becomes the most volume-filling phase in the disk-halo interface. We develop a novel conceptual model of the near-disk gas dynamics in low-redshift L⋆ galaxies: with CRs, the disk-halo interface is filled with CR-driven warm winds and hot super-bubbles that are propagating into the CGM with a small fraction falling back to the disk. Without CRs, most outflows from hot superbubbles are trapped by the existing hot halo and gravity, so typically they form galactic fountains.

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Resolution criteria to avoid artificial clumping in Lagrangian hydrodynamic simulations with a multiphase interstellar medium

Ploeckinger,

Nobels,

Schaller

et al. 2023

Monthly Notices of the Royal Astronomical Society

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Large-scale cosmological galaxy formation simulations typically prevent gas in the interstellar medium (ISM) from cooling below ≈104 K. This has been motivated by the inability to resolve the Jeans mass in molecular gas (≪105 M⊙) which would result in undesired artificial clumping. We show that the classical Jeans criteria derived for Newtonian gravity are not applicable in the simulated ISM if the spacing of resolution elements representing the dense ISM is below the gravitational force softening length and gravity is therefore softened and not Newtonian. We re-derive the Jeans criteria for softened gravity in Lagrangian codes and use them to analyse gravitational instabilities at and below the hydrodynamical resolution limit for simulations with adaptive and constant gravitational softening lengths. In addition, we define criteria for which a numerical runaway collapse of dense gas clumps can occur caused by over-smoothing of the hydrodynamical properties relative to the gravitational force resolution. This effect is illustrated using simulations of isolated disk galaxies with the smoothed particle hydrodynamics code Swift. We also demonstrate how to avoid the formation of artificial clumps in gas and stars by adjusting the gravitational and hydrodynamical force resolutions.

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Testing the effect of resolution on gravitational fragmentation with Lagrangian hydrodynamic schemes

Cited by 4 publications

References 26 publications

On the origin of magnetic fields in stars – II. The effect of numerical resolution

On the origin of magnetic fields in stars – II. The effect of numerical resolution

The impact of cosmic rays on dynamical balance and disc–halo interaction in L⋆ disc galaxies

Resolution criteria to avoid artificial clumping in Lagrangian hydrodynamic simulations with a multiphase interstellar medium

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