A Necessary Condition for Individual Time Steps in SPH Simulations

Saitoh, Takayuki R.; Makino, Junichiro

doi:10.1088/0004-637x/697/2/l99

Cited by 183 publications

(234 citation statements)

References 13 publications

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“…The individual and adaptive timesteps scheme now precisely follows the algorithm proposed by Durier & Dalla Vecchia (2012), which extends the timestep limiter of Saitoh & Makino (2009). The algorithm can be summarised as:…”

Section: Individual and Adaptive Timestepsmentioning

confidence: 99%

Computational issues in chemo-dynamical modelling of the formation and evolution of galaxies

Revaz

Arnaudon

Nichols

et al. 2016

A&A

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Chemo-dynamical N-body simulations are an essential tool for understanding the formation and evolution of galaxies. As the number of observationally determined stellar abundances continues to climb, these simulations are able to provide new constraints on the early star formaton history and chemical evolution inside both the Milky Way and Local Group dwarf galaxies. Here, we aim to reproduce the low α-element scatter observed in metal-poor stars. We first demonstrate that as stellar particles inside simulations drop below a mass threshold, increases in the resolution produce an unacceptably large scatter as one particle is no longer a good approximation of an entire stellar population. This threshold occurs at around 10 3 M , a mass limit easily reached in current (and future) simulations. By simulating the Sextans and Fornax dwarf spheroidal galaxies we show that this increase in scatter at high resolutions arises from stochastic supernovae explosions. In order to reduce this scatter down to the observed value, we show the necessity of introducing a metal mixing scheme into particle-based simulations. The impact of the method used to inject the metals into the surrounding gas is also discussed. We finally summarise the best approach for accurately reproducing the scatter in simulations of both Local Group dwarf galaxies and in the Milky Way.

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Section: Individual and Adaptive Timestepsmentioning

confidence: 99%

Computational issues in chemo-dynamical modelling of the formation and evolution of galaxies

Revaz

Arnaudon

Nichols

et al. 2016

A&A

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“…We use the more recent "pressure-entropy" formulation of SPH which resolves mixing issues when compared with standard "density-entropy" SPH algorithms (see Hopkins 2013;Saitoh & Makino 2013, for further details). Our code additionally implements the time-step limiter of Saitoh & Makino (2009), Durier & Dalla Vecchia (2012 which improves the accuracy of the time integration scheme in situations where there are sudden changes to a particle's internal energy. To prevent artificial fragmentation (Robertson & Kravtsov 2008;Schaye & Dalla Vecchia 2008), we prohibit gas particles from cooling below their effective Jeans temperature which ensures that we are always resolving at least one Jeans mass within a particle's smoothing length.…”

Section: Sph Simulationsmentioning

confidence: 99%

SIMULATOR OF GALAXY MILLIMETER/SUBMILLIMETER EMISSION (SÍGAME): THE [C ii]–SFR RELATIONSHIP OF MASSIVEz= 2 MAIN SEQUENCE GALAXIES

Olsen

Greve

Narayanan

et al. 2015

ApJ

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We present SÍGAME simulations of the C II [ ] 157.7 μm fine structure line emission from cosmological smoothed particle hydrodynamics simulations of seven main sequence galaxies at z=2. Using sub-grid physics prescriptions the gas in our simulations is modeled as a multi-phased interstellar medium comprised of molecular gas residing in giant molecular clouds, an atomic gas phase associated with photo-dissociation regions (PDRs) at the cloud surfaces, and a diffuse, ionized gas phase. Adopting logotropic cloud density profiles and accounting for heating by the local FUV radiation field and cosmic rays by scaling both with local star formation rate (SFR) volume density, we calculate the C II [ ]emission using a photon escape probability formalism. The C II [ ] emission peaks in the central 1 kpc of our galaxies as do the SFR radial profiles, with most C II [ ] (70%) originating in the molecular gas phase, whereas further out (2 kpc), the atomic/PDR gas dominates (90%) the C II [ ] emission, no longer tracing ongoing star formation. Throughout, the ionized gas contribution is negligible (3%). The C II [ ] luminosity versus SFR ( C II [ ]-SFR) relationship, integrated as well as spatially resolved (on scales of 1 kpc), delineated by our simulated galaxies is in good agreement with the corresponding relations observed locally and at high redshifts. In our simulations, the molecular gas dominates the2 ), while atomic/PDR gas takes over at lower SFRs, suggesting a picture in which C II [ ] predominantly traces the molecular gas in high-density/pressure regions where star formation is ongoing, and otherwise reveals the atomic/PDR gas phase.

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“…SPH was also found by Okamoto et al (2003) to cause spurious angular momentum transfer between hot-and cold-phase gas. Special treatments have been proposed by Okamoto et al (2003); Marri & White (2003) and Scannapieco et al (2006) to circumvent the spurious angular momentum transportation by decoupling hot-and cold-phases and by Read et al (2010); Saitoh & Makino (2013) and Hopkins (2013) to prevent this numerical artifact by using density independent formulation of SPH.…”

Section: Introductionmentioning

confidence: 99%

The Formation of a Milky Way-Sized Disk Galaxy. I. A Comparison of Numerical Methods

Zhu

2016

ApJ

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The long-standing challenge of creating a Milky Way-like disk galaxy from cosmological simulations has motivated significant developments in both numerical methods and physical models. We investigate these two fundamental aspects in a new comparison project using a set of cosmological hydrodynamic simulations of a Milky Way-size galaxy. In this study, we focus on the comparison of two particle-based hydrodynamics methods: an improved smoothed particle hydrodynamics (SPH) code Gadget, and a Lagrangian Meshless Finite-Mass (MFM) code Gizmo. All the simulations in this paper use the same initial conditions and physical models, which include star formation, "energy-driven" outflows, metaldependent cooling, stellar evolution and metal enrichment. We find that both numerical schemes produce a late-type galaxy with extended gaseous and stellar disks. However, notable differences are present in a wide range of galaxy properties and their evolution, including star formation history, gas content, disk structure and kinematics. Compared to Gizmo, Gadget simulation produced a larger fraction of cold, dense gas at high redshift which fuels rapid star formation and results in a higher stellar mass by 20% and a lower gas fraction by 10% at z = 0, and the resulting gas disk is smoother and more coherent in rotation due to damping of turbulent motion by the numerical viscosity in SPH, in contrast to the Gizmo simulation which shows more prominent spiral structure. Given its better convergence properties and lower computational cost, we argue that MFM method is a promising alternative to SPH in cosmological hydrodynamic simulations.

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A Necessary Condition for Individual Time Steps in SPH Simulations

Cited by 183 publications

References 13 publications

Computational issues in chemo-dynamical modelling of the formation and evolution of galaxies

Computational issues in chemo-dynamical modelling of the formation and evolution of galaxies

SIMULATOR OF GALAXY MILLIMETER/SUBMILLIMETER EMISSION (SÍGAME): THE [C ii]–SFR RELATIONSHIP OF MASSIVEz= 2 MAIN SEQUENCE GALAXIES

The Formation of a Milky Way-Sized Disk Galaxy. I. A Comparison of Numerical Methods

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