Fully coupled simulation of cosmic reionization. I. numerical methods and tests
Here, we describe an extension of the Enzo code to enable fully coupled radiation hydrodynamical simulation of inhomogeneous reionization in large similar to(100 Mpc)(3) cosmological volumes with thousands to millions of point sources. We solve all dynamical, radiative transfer, thermal, and ionization processes selfconsistently on the same mesh, as opposed to a postprocessing approach which coarsegrains the radiative transfer. But, we employ a simple subgrid model for star formation which we calibrate to observations. The numerical method presented is a modification of an earlier method presented in Reynolds et al. differing principally in the operator splitting algorithm we use to advance the system of equations. Radiation transport is done in the gray fluxlimited diffusion (FLD) approximation, which is solved by implicit time integration split off from the gas energy and ionization equations, which are solved separately. This results in a faster and more robust scheme for cosmological applications compared to the earlier method. The FLD equation is solved using the hypre optimally scalable geometric multigrid solver from LLNL. By treating the ionizing radiation as a grid field as opposed to rays, our method is scalable with respect to the number of ionizing sources, limited only by the parallel scaling propertiesmore »
 Authors:

^{[1]};
^{[2]};
^{[1]};
^{[3]};
^{[4]}
 Univ. of California, San Diego, CA (United States)
 Southern Methodist Univ., Dallas, TX (United States)
 Univ. of California, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
 Georgia Inst. of Technology, Atlanta, GA (United States)
 Publication Date:
 Grant/Contract Number:
 AC0500OR22725; AST0808184; AST1109243
 Type:
 Accepted Manuscript
 Journal Name:
 The Astrophysical Journal. Supplement Series (Online)
 Additional Journal Information:
 Journal Name: The Astrophysical Journal. Supplement Series (Online); Journal Volume: 216; Journal Issue: 1; Journal ID: ISSN 15384365
 Publisher:
 American Astronomical Society/IOP
 Research Org:
 Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
 Sponsoring Org:
 USDOE; National Science Foundation (NSF)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 79 ASTRONOMY AND ASTROPHYSICS; cosmology: theory; methods: numerical; radiative transfer; ADAPTIVE MESH REFINEMENT; COSMOLOGICAL RADIATIVETRANSFER; PROBE WMAP OBSERVATIONS; FLUXLIMITED DIFFUSION; PIECEWISE PARABOLIC METHOD; POPULATIONIII STARS; HYDROGEN REIONIZATION; INTERGALACTIC ME
 OSTI Identifier:
 1286996
Norman, Michael L., Reynolds, Daniel R., So, Geoffrey C., Harkness, Robert P., and Wise, John H.. Fully coupled simulation of cosmic reionization. I. numerical methods and tests. United States: N. p.,
Web. doi:10.1088/00670049/216/1/16.
Norman, Michael L., Reynolds, Daniel R., So, Geoffrey C., Harkness, Robert P., & Wise, John H.. Fully coupled simulation of cosmic reionization. I. numerical methods and tests. United States. doi:10.1088/00670049/216/1/16.
Norman, Michael L., Reynolds, Daniel R., So, Geoffrey C., Harkness, Robert P., and Wise, John H.. 2015.
"Fully coupled simulation of cosmic reionization. I. numerical methods and tests". United States.
doi:10.1088/00670049/216/1/16. https://www.osti.gov/servlets/purl/1286996.
@article{osti_1286996,
title = {Fully coupled simulation of cosmic reionization. I. numerical methods and tests},
author = {Norman, Michael L. and Reynolds, Daniel R. and So, Geoffrey C. and Harkness, Robert P. and Wise, John H.},
abstractNote = {Here, we describe an extension of the Enzo code to enable fully coupled radiation hydrodynamical simulation of inhomogeneous reionization in large similar to(100 Mpc)(3) cosmological volumes with thousands to millions of point sources. We solve all dynamical, radiative transfer, thermal, and ionization processes selfconsistently on the same mesh, as opposed to a postprocessing approach which coarsegrains the radiative transfer. But, we employ a simple subgrid model for star formation which we calibrate to observations. The numerical method presented is a modification of an earlier method presented in Reynolds et al. differing principally in the operator splitting algorithm we use to advance the system of equations. Radiation transport is done in the gray fluxlimited diffusion (FLD) approximation, which is solved by implicit time integration split off from the gas energy and ionization equations, which are solved separately. This results in a faster and more robust scheme for cosmological applications compared to the earlier method. The FLD equation is solved using the hypre optimally scalable geometric multigrid solver from LLNL. By treating the ionizing radiation as a grid field as opposed to rays, our method is scalable with respect to the number of ionizing sources, limited only by the parallel scaling properties of the radiation solver. We test the speed and accuracy of our approach on a number of standard verification and validation tests. We show by direct comparison with Enzo's adaptive ray tracing method Moray that the wellknown inability of FLD to cast a shadow behind opaque clouds has a minor effect on the evolution of ionized volume and mass fractions in a reionization simulation validation test. Finally, we illustrate an application of our method to the problem of inhomogeneous reionization in a 80 Mpc comoving box resolved with 3200(3) Eulerian grid cells and dark matter particles.},
doi = {10.1088/00670049/216/1/16},
journal = {The Astrophysical Journal. Supplement Series (Online)},
number = 1,
volume = 216,
place = {United States},
year = {2015},
month = {1}
}