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.
Cosmological hydrodynamical simulations of clustering dark energy with Nefertiti
The University of Tokyo（东京大学）；Observatoire de Paris, Université PSL, Sorbonne Université, CNRS（巴黎天文台，PSL大学，索邦大学，法国国家科学研究中心）；Université Paris-Cité（巴黎西岱大学）；Max–Planck–Institut für Astrophysik（马克斯·普朗克天体物理研究所）；École Polytechnique（巴黎综合理工学院）
Calibrating cosmological radiative transfer simulations with Lyman alpha forest data: Evidence for large spatial UV background fluctuations at z ~ 5.6 - 5.8 due to rare bright sources
Redshift Space Distortion of 21cm line at 1<z<5 with Cosmological Hydrodynamic Simulations
在k>1h/Mpc的标度下，测量了红移1<z3的中性氢气21 cm谱线的标度依赖性和红移依赖性<5 using full cosmological hydrodynamic simulations by taking the ratios between the power spectra of HI- dark matter cross correlation and dark matter auto-correlation. The neutral hydrogen distribution is computed in full cosmological hydrodynamic simulations including star formation and supernova feedback under a uniform ultra-violet background radiation. We find a significant scale dependence of HI bias at z>，但在较低的红移z<3时，它基本不变.在相同的红移范围内，HI偏置的红移演化相对慢于类星体。我们还测量了HI气体的红移空间畸变（RSD），以探索HI团簇的性质。拟合广泛应用的理论预测，我们发现，恒定的偏差是一致的，直接从实空间功率谱测量，和速度色散是轻微一…
Interpreting Cosmological Information from Neural Networks in the Hydrodynamic Universe
Foundation for Research and Technology—Hellas（希腊研究与技术基金会）；Department of Physics, University of Crete（克里特大学物理系）；Department of Astrophysical Sciences, Princeton University（普林斯顿大学天体物理学系）；Center for Computational Astrophysics, Flatiron Institute（平托研究所计算天体物理中心）
