Messenger Monte Carlo MAPPINGS V (M3)-A Self-consistent, Three-dimensional Photoionization Code

The Messenger Interface Monte Carlo Mappings V (M³) is a photoionization code adopting the fully self-consistent Monte Carlo radiative transfer (MCRT) technique, which presents a major advance over previous photoionization models with simple geometries. M³ is designed for modeling nebulae in arbitrary three-dimensional geometries. In this paper, we describe the MCRT technique and the microphysics implemented in M³, including photoionization, collisional ionization, free-free and free-bound recombination, and two-photon radiation. We put M³ through the Lexington/Meudon benchmarks to test the reliability of the new code. We apply M³ to three H II region models with fiducial geometries, demonstrating that M³ is capable of dealing with nebulae with complex geometries. M³ is a promising tool for understanding emission-line behavior in the era of SDSS-V/LVM and James Webb Space Telescope, which will provide high-quality data of spatially resolved nearby H II regions and highly turbulent local and high-redshift H II regions.