On the Proper Use of the Reduced Speed of Light Approximation

Abstract

I show that the Reduced Speed of Light (RSL) approximation, when used properly (i.e. as originally designed - only for the local sources but not for the cosmic background), remains a highly accurate numerical method for modeling cosmic reionization. Simulated ionization and star formation histories from the "Cosmic Reionization On Computers" (CROC) project are insensitive to the adopted value of the reduced speed of light for as long as that value does not fall below about 10% of the true speed of light. A recent claim of the failure of the RSL approximation in the Illustris reionization model appears to be due to the effective speed of light being reduced in the equation for the cosmic background too, and, hence, illustrates the importance of maintaining the correct speed of light in modeling the cosmic background.

arXiv commentSubmitted to ApJ

References in corpus (10)

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• The SPHINX Cosmological Simulations of the First Billion Years: the Impact of Binary Stars on Reionization
• The THESAN project: properties of the intergalactic medium and its connection to Reionization-era galaxies
• The THESAN project: Lyman-alpha emission and transmission during the Epoch of Reionization
• Heating of the Intergalactic Medium by Hydrogen Reionization
• The short ionizing photon mean free path at z=6 in Cosmic Dawn III, a new fully-coupled radiation-hydrodynamical simulation of the Epoch of Reionization
• Galactic ionising photon budget during the Epoch of Reionisation in the Cosmic Dawn II simulation
• Lyman-alpha opacities at z=4-6 require low mass, radiatively-suppressed galaxies to drive cosmic reionization
• Impact of the reduced speed of light approximation on ionization front velocities in cosmological simulations of the epoch of reionization
• A deep learning model to emulate simulations of cosmic reionization
• Dusty Cloud Acceleration by Radiation Pressure in Rapidly Star-Forming Galaxies
• Impact of the reduced speed of light approximation on the post-overlap neutral hydrogen fraction in numerical simulations of the epoch of reionization
• A finite volume method for two-moment cosmic-ray hydrodynamics on a moving mesh
• SPICE: the connection between cosmic reionisation and stellar feedback in the first galaxies
• Population III star formation in an X-ray background: III. Periodic radiative feedback and luminosity induced by elliptical orbits
• DUSTiER (DUST in the Epoch of Reionization): dusty galaxies in cosmological radiation-hydrodynamical simulations of the Epoch of Reionization with RAMSES-CUDATON
• On the accuracy of common moment-based radiative transfer methods for simulating reionization
• The THESAN project: Lyman-alpha emitter luminosity function calibration