Light-Cone Effect of Radiation Fields in Cosmological Radiative Transfer Simulations

TL;DR

This paper introduces an efficient method to incorporate the light-cone effect in cosmological radiative transfer simulations, improving accuracy in modeling radiation propagation from sources like the first stars.

Contribution

The authors develop a FFT-based approach to calculate retarded-time radiation fields, enabling accurate and computationally feasible light-cone effect inclusion in simulations.

Findings

Method accurately models time-delayed radiation fields.

Efficient FFT-based convolution simplifies implementation.

Applicable to high-redshift astrophysics and Lyman-Werner photons.

Abstract

We present a novel method to implement time-delayed propagation of radiation fields in cosmological radiative transfer simulations. Time-delayed propagation of radiation fields requires construction of retarded-time fields by tracking the location and lifetime of radiation sources along the corresponding light-cones. Cosmological radiative transfer simulations have, until now, ignored this "light-cone effect" or implemented ray-tracing methods that are computationally demanding. We show that radiative transfer calculation of the time-delayed fields can be easily achieved in numerical simulations when periodic boundary conditions are used, by calculating the time-discretized retarded-time Green's function using the Fast Fourier Transform (FFT) method and convolving it with the source distribution. We also present a direct application of this method to the long-range radiation field of Lyman-Werner band photons, which is important in the high-redshift astrophysics with first stars.