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.

Submitted to ApJ

References in corpus (3)

• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• Effects of Baryons and Dissipation on the Matter Power Spectrum
• Cosmic Reionization On Computers I. Design and Calibration of Simulations

Cited by in corpus (10)

• 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
• 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
• Lyman-alpha opacities at z=4-6 require low mass, radiatively-suppressed galaxies to drive cosmic reionization
• SPICE: the connection between cosmic reionisation and stellar feedback in the first galaxies
• A finite volume method for two-moment cosmic-ray hydrodynamics on a moving mesh
• 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
• The THESAN project: Lyman-alpha emitter luminosity function calibration
• On the accuracy of common moment-based radiative transfer methods for simulating reionization