ART2: a 3D parallel multiwavelength radiative transfer code for continuum and atomic and molecular lines

Abstract

ABSTRACT ART2 is a 3D multiwavelength Monte Carlo radiative transfer (RT) code that couples continuum and emission lines to track the propagation of photons and their interactions with the interstellar medium (ISM). The original ART2 has been extensively applied to hydrodynamics simulations to study panchromatic properties of galaxies and ISM. Here, we describe new implementations of non-local thermodynamic equilibrium RT of molecular and atomic fine structure emission lines, and the parallelization of the code using a number of novel methods. The new ART2 can efficiently and self-consistently produce a full spectrum that includes both continuum and lines such as [C ii], [N ii], [O iii], Ly α, and CO. These essential features, together with the multiphase ISM model and the adaptive grid, make ART2 a multipurpose code to study multiwavelength properties of a wide range of astrophysical systems from planetary discs to large-scale structures. To demonstrate the capability of the new ART2, we applied it to two hydrodynamics simulations: the zoom-in Milky Way Simulation to obtain panchromatic properties of individual galaxies, and the large-scale IllustrisTNG100 Simulation to obtain global properties such as the line intensity mappings. These products are vital for a broad array of studies. By enabling direct comparison between numerical simulations and multiband observations, ART2 provides a crucial theoretical framework for the understanding of existing and future surveys, and the synergy between multiband galaxy surveys and line intensity mappings. Therefore, ART2 is a powerful and versatile tool to bridge the gap between theories and observations of cosmic structures.