C2-ray: A new method for photon-conserving transport of ionizing radiation

By G. Mellema, Ilian Iliev, M. Alvarez, P. R. S. Astron, Dwingeloo, The Netherlands., L. Observatory, Cita, Toronto, Canada. and 3 more. 2005

181 citations recorded by the source corpus.

Abstract We present a new numerical method for calculating the transfer of ionizing radiation, called C2-ray (conservative, causal ray-tracing method). The transfer of ionizing radiation in diffuse gas presents a special challenge to most numerical methods which involve time- and spatial-differencing. Standard approaches to radiative transport require that grid cells must be small enough to be optically-thin while time steps are small enough that ionization fronts do not cross a cell in a single time step. This quickly becomes prohibitively expensive. We have developed an algorithm which overcomes these limitations and is, therefore, orders of magnitude more efficient. The method is explicitly photon-conserving, so the depletion of ionizing photons by bound-free opacity is guaranteed to equal the photoionizations these photons caused. As a result, grid cells can be large and very optically-thick without loss of accuracy. The method also uses an analytical relaxation solution for the ionization rate equations for each time step which can accommodate time steps which greatly exceed the characteristic ionization and ionization front crossing times. Together, these features make it possible to integrate the equation of transfer along a ray with many fewer cells and time steps than previous methods. For multi-dimensional calculations, the code utilizes short-characteristics ray tracing. The method scales as the product of the number of grid cells and the number of sources. C2-ray is well-suited for coupling radiative transfer to gas and N-body dynamics methods, on both fixed and adaptive grids, without imposing additional limitations on the time step and grid spacing. We present several tests of the code involving propagation of ionization fronts in one and three dimensions, in both homogeneous and inhomogeneous density fields. We compare to analytical solutions for the ionization front position and velocity, some of which we derive here for the first time. As an illustration, we apply C2-ray to simulate cosmic reionization in three-dimensional inhomogeneous cosmological density field. We also apply it to the problem of I-front trapping in a dense clump, using both a fixed and an adaptive grid.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

COSMIC MICROWAVE BACKGROUND CONSTRAINTS ON THE DURATION AND TIMING OF REIONIZATION FROM THE SOUTH POLE TELESCOPE (2011, background): “D radiative transfer codes (e.g., Gnedin 2000; Sokasian et al. 2001; Razoumov et al. 2002; Ciardi et al. 2003; Mellema et al. 2006; McQuinn et al. 2007b; Semelin et al. 2007; Trac & Cen 2007a; Altay et al. 2008; Aubert & Teyssier 2008; Finlator et al. 2009; Petkova & Springel 2009).”
Simulations and Analytic Calculations of Bubble Growth during Hydrogen Reionization (2006, background): “…(see e.g. Gnedin 2000; Razoumov et al. 2002; Ciardi et al. 2003; Sokasian et al. 2002; Sokasian et al. 2001; Furlanetto et al. 2004b,a; Kohler et al. 2005; Iliev et al. 2005; Mellema et al. 2006) is, however, required to constrain the topology of reionization from current and future observations.”
Simulating cosmic reionization at large scales – II. The 21-cm emission features and statistical signals (2006, methodology): “The code has been tested in detail against available ana ytical solutions (Mellema et al. 2006) and in comparison with ot er radiative transfer codes (Iliev et al. 2006).”
LOFAR: The LOw-Frequency ARray (2013, background): “…that we may expect an evolving complex patch work of neutral (HI) and ionized hydrogen (HII) regions (Gnedin & Abel 2001; Ciardi et al. 2003; Whalen & Norman 2006; Mellema et al. 2006; Zahn et al. 2007; Mesinger & Furlanetto 2007; Thomas et al. 2009; Thomas & Zaroubi 2011; Ciardi et al. 2012).”
Self-regulated reionization (2006, methodology): “Attempts to simulate reionization in a CDM universe this way include Ciardi et al. (2000); Nakamoto et al. (2001); Razoumovet al. (2002); Ciardi et al. (2003b); Sokasian et al. (2003); Ilievet al. (2006b); Mellema et al. (2006b).”
Lyα Emitting Galaxies as a Probe of Reionisation (2014, background): “A number of groups have developed codes that can perform these calculations in 3D (e.g. Gnedin 2000; Sokasian, Abel, & Hernquist 2001; Ciardi, Stoehr, & White 2003; Mellema et al. 2006; Trac & Cen 2007; Pawlik & Schaye 2008; Finlator, Özel, & Davé 2009).”
ramses-rt: radiation hydrodynamics in the cosmological context (2013, methodology): “A few others that have been used for published astrophysical (ionizing) RHD simulations but without a co-evolving cosmology are Mellema et al. (2006), Susa (2006), Whalen & Norman (2006) and Baek et al. (2009).”
Cosmological radiative transfer codes comparison project – I. The static density field tests (2006, unknown): “The code is currently used for large-scale simulations of cosmic reionization and its observability (Iliev et al. 2006b; Mellema et al. 2006b) on grid sizes up to 4063 and up to more than 105 ionizing sources.”
Simulating Cosmic Reionization at Large Scales I: the Geometry of Reionization (2005, methodology): “The patchiness of reionization results in a significant increase of both the neutral- and ionized-gas density fluctuations, with important implications for statistical observations of reionization at, e.g., the 21-cm line of neutral hydrogen (Mellema et al. 2006b) and small-scale CMB anisotropies.”
Comparison of reionization models: radiative transfer simulations and approximate, seminumeric models (2010, background): “D radiative transfer (RT) codes (e.g. Gnedin 2000; Razoumov et al. 2002; Ciardi et al. 2003; Sokasian et al. 2001; Mellema et al. 2006; McQuinn et al. 2007b; Semelin et al. 2007; Trac & Cen 2007; Altay et al. 2008; Aubert & Teyssier 2008; Finlator et al. 2009; Petkova & Springel 2009; see the…”
ENZO: AN ADAPTIVE MESH REFINEMENT CODE FOR ASTROPHYSICS (2013, background): “We equate the photo-ionization rate to the absorption rate, resulting in photon conservation (Abel et al. 1999; Mellema et al. 2006).”