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Title:

cosmological simulation code GADGET

Description:

We present a novel numerical implementation of radiative transfer in the cosmological smoothed particle hydrodynamics (SPH) simulation code GADGET. It is based on a fast, robust and photon-conserving integration scheme where the radiation transport problem is approximated in terms of moments of the transfer equation and by using a variable Eddin...

We present a novel numerical implementation of radiative transfer in the cosmological smoothed particle hydrodynamics (SPH) simulation code GADGET. It is based on a fast, robust and photon-conserving integration scheme where the radiation transport problem is approximated in terms of moments of the transfer equation and by using a variable Eddington tensor as a closure relation, following the ‘OTVET’-suggestion of Gnedin & Abel. We derive a suitable anisotropic diffusion operator for use in the SPH discretization of the local photon transport, and we combine this with an implicit solver that guarantees robustness and photon conservation. This entails a matrix inversion problem of a huge, sparsely populated matrix that is distributed in memory in our parallel code. We solve this task iteratively with a conjugate gradient scheme. Finally, to model photon sink processes we consider ionisation and recombination processes of hydrogen, which is represented with a chemical network that is evolved with an implicit time integration scheme. We present several tests of our implementation, including single and multiple sources in static uniform density fields with and without temperature evolution, shadowing by a dense clump, and multiple sources in a static cosmological density field. All tests agree quite well with analytical computations or with predictions from other radiative transfer codes, except for shadowing. However, unlike most other radiative transfer codes presently in use for studying reionisation, our new method can be used on-the-fly during dynamical cosmological simulation, allowing simultaneous treatments of galaxy formation and the reionisation process of the Universe. Key words: radiative transfer- methods: numerical Minimize

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The Pennsylvania State University CiteSeerX Archives

Year of Publication:

2012-12-03

Source:

http://arxiv.org/pdf/0812.1801v1.pdf

http://arxiv.org/pdf/0812.1801v1.pdf Minimize

Document Type:

text

Language:

en

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Metadata may be used without restrictions as long as the oai identifier remains attached to it.

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Title:

cosmological simulation code GADGET

Description:

We present a novel numerical implementation of radiative transfer in the cosmological smoothed particle hydrodynamics (SPH) simulation code GADGET. It is based on a fast, robust and photon-conserving integration scheme where the radiation transport problem is approximated in terms of moments of the transfer equation and by using a variable Eddin...

We present a novel numerical implementation of radiative transfer in the cosmological smoothed particle hydrodynamics (SPH) simulation code GADGET. It is based on a fast, robust and photon-conserving integration scheme where the radiation transport problem is approximated in terms of moments of the transfer equation and by using a variable Eddington tensor as a closure relation, following the ‘OTVET’-suggestion of Gnedin & Abel. We derive a suitable anisotropic diffusion operator for use in the SPH discretization of the local photon transport, and we combine this with an implicit solver that guarantees robustness and photon conservation. This entails a matrix inversion problem of a huge, sparsely populated matrix that is distributed in memory in our parallel code. We solve this task iteratively with a conjugate gradient scheme. Finally, to model photon sink processes we consider ionisation and recombination processes of hydrogen, which is represented with a chemical network that is evolved with an implicit time integration scheme. We present several tests of our implementation, including single and multiple sources in static uniform density fields with and without temperature evolution, shadowing by a dense clump, and multiple sources in a static cosmological density field. All tests agree quite well with analytical computations or with predictions from other radiative transfer codes, except for shadowing. However, unlike most other radiative transfer codes presently in use for studying reionisation, our new method can be used on-the-fly during dynamical cosmological simulation, allowing simultaneous treatments of galaxy formation and the reionisation process of the Universe. Key words: radiative transfer- methods: numerical Minimize

Contributors:

The Pennsylvania State University CiteSeerX Archives

Year of Publication:

2012-11-27

Source:

http://arxiv.org/pdf/0812.1801v2.pdf

http://arxiv.org/pdf/0812.1801v2.pdf Minimize

Document Type:

text

Language:

en

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Metadata may be used without restrictions as long as the oai identifier remains attached to it.

Metadata may be used without restrictions as long as the oai identifier remains attached to it. Minimize

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Title:

Numerical Radiative Transfer and the Hydrogen Reionization of the Universe

Publisher:

Ludwig-Maximilians-Universität München

Year of Publication:

2011-03-18

Document Type:

Dissertation ; NonPeerReviewed

Subjects:

Fakultät für Physik

Fakultät für Physik Minimize

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http://edoc.ub.uni-muenchen.de/12898/

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Title:

An implementation of radiative transfer in the cosmological simulation code GADGET

Author:

Description:

We present a novel numerical implementation of radiative transfer in the cosmological smoothed particle hydrodynamics (SPH) simulation code <scp>gadget</scp>. It is based on a fast, robust and photon–conserving integration scheme where the radiation transport problem is approximated in terms of moments of the transfer equation and by using a var...

We present a novel numerical implementation of radiative transfer in the cosmological smoothed particle hydrodynamics (SPH) simulation code <scp>gadget</scp>. It is based on a fast, robust and photon–conserving integration scheme where the radiation transport problem is approximated in terms of moments of the transfer equation and by using a variable Eddington tensor as a closure relation, following the Optically Thin Variable Eddington Tensor suggestion of Gnedin & Abel. We derive a suitable anisotropic diffusion operator for use in the SPH discretization of the local photon transport, and we combine this with an implicit solver that guarantees robustness and photon conservation. This entails a matrix inversion problem of a huge, sparsely populated matrix that is distributed in memory in our parallel code. We solve this task iteratively with a conjugate gradient scheme. Finally, to model photon sink processes we consider ionization and recombination processes of hydrogen, which is represented with a chemical network that is evolved with an implicit time integration scheme. We present several tests of our implementation, including single and multiple sources in static uniform density fields with and without temperature evolution, shadowing by a dense clump and multiple sources in a static cosmological density field. All tests agree quite well with analytical computations or with predictions from other radiative transfer codes, except for shadowing. However, unlike most other radiative transfer codes presently in use for studying re–ionization, our new method can be used on–the–fly during dynamical cosmological simulation, allowing simultaneous treatments of galaxy formation and the re–ionization process of the Universe. Minimize

Publisher:

Oxford University Press

Year of Publication:

2009-07-01 00:00:00.0

Document Type:

TEXT

Language:

en

Subjects:

Papers

Papers Minimize

DDC:

520 Astronomy & allied sciences *(computed)*

Rights:

Copyright (C) 2009, Oxford University Press

Copyright (C) 2009, Oxford University Press Minimize

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Title:

Radiative feedback and cosmic molecular gas: numerical method

Description:

We present the results from self-consistent numerical simulations of cosmic structure formation with a multifrequency radiative transfer scheme and non-equilibrium molecular chemistry of 13 primordial species (e−, H, H+, H−, He, He+, He++, H 2 , H<f> </f>, D, D+, HD and HeH+), performed using the simulation code <scp>gadget</scp>. We describe ou...

We present the results from self-consistent numerical simulations of cosmic structure formation with a multifrequency radiative transfer scheme and non-equilibrium molecular chemistry of 13 primordial species (e−, H, H+, H−, He, He+, He++, H 2 , H<f> </f>, D, D+, HD and HeH+), performed using the simulation code <scp>gadget</scp>. We describe our implementation and we show tests for ionized sphere expansion in a static and dynamic density field around a central radiative source, and for cosmological abundance evolution coupled with the cosmic microwave background radiation. As a demonstrative application of radiative feedback on molecular gas, we also run cosmological simulations of early structure formation in a ∼1-Mpc sized box. Our tests agree well with analytical and numerical expectations. Consistent with other works, we find that ionization fronts from central sources can boost H 2 fractions in shock-compressed gas. The tight dependence on H 2 also leads to a corresponding boost of HD fractions. We see a strong lowering of the typical molecular abundances up to several orders of magnitude, which partially hinders further gas collapse of pristine neutral gas. This clearly suggests the need for reionized gas or metal cooling in the formation of the following generation of structures. Minimize

Publisher:

Oxford University Press

Year of Publication:

2012-06-01 00:00:00.0

Document Type:

TEXT

Language:

en

Subjects:

Papers

Papers Minimize

DDC:

520 Astronomy & allied sciences *(computed)*

Rights:

Copyright (C) 2012, Oxford University Press

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Title:

A novel approach for accurate radiative transfer in cosmological hydrodynamic simulations

Author:

Description:

We present a numerical implementation of radiative transfer based on an explicitly photon-conserving advection scheme, where radiative fluxes over the cell interfaces of a structured or unstructured mesh are calculated with a second-order reconstruction of the intensity field. The approach employs a direct discretisation of the radiative transfe...

We present a numerical implementation of radiative transfer based on an explicitly photon-conserving advection scheme, where radiative fluxes over the cell interfaces of a structured or unstructured mesh are calculated with a second-order reconstruction of the intensity field. The approach employs a direct discretisation of the radiative transfer equation in Boltzmann form with adjustable angular resolution that in principle works equally well in the optically thin and optically thick regimes. In our most general formulation of the scheme, the local radiation field is decomposed into a linear sum of directional bins of equal solid-angle, tessellating the unit sphere. Each of these "cone-fields" is transported independently, with constant intensity as a function of direction within the cone. Photons propagate at the speed of light (or optionally using a reduced speed of light approximation to allow larger timesteps), yielding a fully time-dependent solution of the radiative transfer equation that can naturally cope with an arbitrary number of sources, as well as with scattering. The method casts sharp shadows, subject to the limitations induced by the adopted angular resolution. If the number of point sources is small and scattering is unimportant, our implementation can alternatively treat each source exactly in angular space, producing shadows whose sharpness is only limited by the grid resolution. A third hybrid alternative is to treat only a small number of the locally most luminous point sources explicitly, with the rest of the radiation intensity followed in a radiative diffusion approximation. We have implemented the method in the moving-mesh code {\small AREPO}, where it is coupled to the hydrodynamics in an operator splitting approach that subcycles the radiative transfer alternatingly with the hydrodynamical evolution steps. ; Comment: 20 pages, 23 figures, submitted to MNRAS Minimize

Year of Publication:

2010-12-05

Document Type:

text

Subjects:

Astrophysics - Cosmology and Extragalactic Astrophysics

Astrophysics - Cosmology and Extragalactic Astrophysics Minimize

DDC:

535 Light & infrared & ultraviolet phenomena *(computed)*

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Title:

Radiative feedback and cosmic molecular gas: numerical method

Description:

We present results from self-consistent 3D numerical simulations of cosmic structure formation with a multi-frequency radiative transfer scheme and non-equilibrium molecular chemistry of 13 primordial species (e-, H, H+, H-, He, He+, He++, H2, H2+, D, D+, HD, HeH+), performed by using the simulation code GADGET. We describe our implementation an...

We present results from self-consistent 3D numerical simulations of cosmic structure formation with a multi-frequency radiative transfer scheme and non-equilibrium molecular chemistry of 13 primordial species (e-, H, H+, H-, He, He+, He++, H2, H2+, D, D+, HD, HeH+), performed by using the simulation code GADGET. We describe our implementation and show tests for ionized sphere expansion in a static and dynamic density field around a central radiative source, and for cosmological abundance evolution coupled with the cosmic microwave background radiation. As a demonstrative application of radiative feedback on molecular gas, we run also cosmological simulations of early structure formation in a ~1Mpc size box. Our tests agree well with analytical and numerical expectations. Consistently with other works, we find that ionization fronts from central sources can boost H2 fractions in shock-compressed gas. The tight dependence on H2 lead to a corresponding boost of HD fractions, as well. We see a strong lowering of the the typical molecular abundances up to several orders of magnitudes which partially hinders further gas collapse of pristine neutral gas, and clearly suggests the need of re-ionized gas or metal cooling for the formation of the following generation of structures. ; Comment: 16 pages, 9 figures; title changed; discussion extended; in press on MNRAS Minimize

Year of Publication:

2011-10-03

Document Type:

text

Subjects:

Astrophysics - Cosmology and Extragalactic Astrophysics ; Mathematical Physics ; Physics - Computational Physics

Astrophysics - Cosmology and Extragalactic Astrophysics ; Mathematical Physics ; Physics - Computational Physics Minimize

DDC:

520 Astronomy & allied sciences *(computed)*

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Title:

Simulations of galaxy formation with radiative transfer: Hydrogen reionization and radiative feedback

Author:

Description:

We carry out hydrodynamical simulations of galaxy formation that simultaneously follow radiative transfer of hydrogen-ionizing photons, based on the optically-thin variable Eddington tensor approximation as implemented in the {\small GADGET} code. We consider only star-forming galaxies as sources and examine to what extent they can yield a reaso...

We carry out hydrodynamical simulations of galaxy formation that simultaneously follow radiative transfer of hydrogen-ionizing photons, based on the optically-thin variable Eddington tensor approximation as implemented in the {\small GADGET} code. We consider only star-forming galaxies as sources and examine to what extent they can yield a reasonable reionization history and thermal state of the intergalactic medium at redshifts around $z\sim 3$. This serves as an important benchmark for our self-consistent methodology to simulate galaxy formation and reionization, and for future improvements through accounting of other sources and other wavelength ranges. We find that star formation alone is sufficient for reionizing the Universe by redshift $z\sim6$. For a suitable choice of the escape fraction and the heating efficiency, our models are approximately able to account at the same time for the one-point function and the power spectrum of the Lyman-$\alpha$ forest. The radiation field has an important impact on the star formation rate density in our simulations and significantly lowers the gaseous and stellar fractions in low-mass dark matter halos. Our results thus directly demonstrate the importance of radiative feedback for galaxy formation. The spatial and temporal importance of this effect can be studied accurately with the modelling technique explored here, allowing more faithful simulations of galaxy formation. ; Comment: 14 pages, 17 figures, published in MNRAS Minimize

Year of Publication:

2010-08-26

Document Type:

text

Subjects:

Astrophysics - Cosmology and Extragalactic Astrophysics

Astrophysics - Cosmology and Extragalactic Astrophysics Minimize

DDC:

520 Astronomy & allied sciences *(computed)*

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Title:

GLAMER Part I: A Code for Gravitational Lensing Simulations with Adaptive Mesh Refinement

Author:

Description:

A computer code is described for the simulation of gravitational lensing data. The code incorporates adaptive mesh refinement in choosing which rays to shoot based on the requirements of the source size, location and surface brightness distribution or to find critical curves/caustics. A variety of source surface brightness models are implemented...

A computer code is described for the simulation of gravitational lensing data. The code incorporates adaptive mesh refinement in choosing which rays to shoot based on the requirements of the source size, location and surface brightness distribution or to find critical curves/caustics. A variety of source surface brightness models are implemented to represent galaxies and quasar emission regions. The lensing mass can be represented by point masses (stars), smoothed simulation particles, analytic halo models, pixelized mass maps or any combination of these. The deflection and beam distortions (convergence and shear) are calculated by modified tree algorithm when halos, point masses or particles are used and by FFT when mass maps are used. The combination of these methods allow for a very large dynamical range to be represented in a single simulation. Individual images of galaxies can be represented in a simulation that covers many square degrees. For an individual strongly lensed quasar, source sizes from the size of the quasar's host galaxy (~ 100 kpc) down to microlensing scales (~ 10^-4 pc) can be probed in a self consistent simulation. Descriptions of various tests of the code's accuracy are given. ; Comment: 13 pages, 9 figures, submitted to MNRAS, corrected some typos, replaced figure 9 after problem with numerical precision was discovered Minimize

Year of Publication:

2013-12-04

Document Type:

text

Subjects:

Astrophysics - Cosmology and Extragalactic Astrophysics

Astrophysics - Cosmology and Extragalactic Astrophysics Minimize

DDC:

520 Astronomy & allied sciences *(computed)*

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Title:

GLAMER Part II: Multiple Plane Gravitational Lensing

Author:

Description:

We present an extension to multiple planes of the gravitational lensing code {\small GLAMER}. The method entails projecting the mass in the observed light-cone onto a discrete number of lens planes and inverse ray-shooting from the image to the source plane. The mass on each plane can be represented as halos, simulation particles, a projected ma...

We present an extension to multiple planes of the gravitational lensing code {\small GLAMER}. The method entails projecting the mass in the observed light-cone onto a discrete number of lens planes and inverse ray-shooting from the image to the source plane. The mass on each plane can be represented as halos, simulation particles, a projected mass map extracted form a numerical simulation or any combination of these. The image finding is done in a source oriented fashion, where only regions of interest are iteratively refined on an initially coarse image plane grid. The calculations are performed in parallel on shared memory machines. The code is able to handle different types of analytic halos (NFW, NSIE, power-law, etc.), haloes extracted from numerical simulations and clusters constructed from semi-analytic models ({\small MOKA}). Likewise, there are several different options for modeling the source(s) which can be distributed throughout the light-cone. The distribution of matter in the light-cone can be either taken from a pre-existing N-body numerical simulations, from halo catalogs, or are generated from an analytic mass function. We present several tests of the code and demonstrate some of its applications such as generating mock images of galaxy and galaxy cluster lenses. ; Comment: 14 pages, 10 figures, submitted to MNRAS Minimize

Year of Publication:

2013-12-05

Document Type:

text

Subjects:

Astrophysics - Cosmology and Extragalactic Astrophysics

Astrophysics - Cosmology and Extragalactic Astrophysics Minimize

DDC:

520 Astronomy & allied sciences *(computed)*

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