torus-3dpdr: a self-consistent code treating three-dimensional photoionization and photodissociation regions

Abstract

The interaction of ionizing and far-ultraviolet radiation with the interstellar medium is of great importance. It results in the formation of regions in which the gas is ionized, beyond which are photodissociation regions (PDRs) in which the gas transitions to its atomic and molecular form. Several numerical codes have been implemented to study these two main phases of the interstellar medium either dynamically or chemically. In this paper we present TORUS-3DPDR, a new self-consistent code for treating the chemistry of three-dimensional photoionization and photodissociation regions. It is an integrated code coupling the two codes TORUS, a hydrodynamics and Monte Carlo radiation transport code, and 3D-PDR, a photodissociation regions code. The new code uses a Monte Carlo radiative transfer scheme to account for the propagation of the ionizing radiation including the diffusive component as well as a ray-tracing scheme based on the HEALPIX package in order to account for the escape probability and column density calculations. Here, we present the numerical techniques we followed and we show the capabilities of the new code in modelling three-dimensional objects including single or multiple sources. We discuss the effects introduced by the diffusive component of the UV field in determining the thermal balance of PDRs as well as the effects introduced by a multiple sources treatment of the radiation field. We find that diffuse radiation can positively contribute to the formation of CO. With this new code, three-dimensional synthetic observations for the major cooling lines are possible, for making feasible a detailed comparison between hydrodynamical simulations and observations.

ALMA Detects CO(3–2) within a Super Star Cluster in NGC 5253

“…Tielens 1999; Bisbas et al 2015). At a density of n crit = 30, 000 cm −3 (for T=300K), the minimum cloud column corresponds to a distance of 0.04 pc = 8000 AU, for a Galactic A V /(N H + 2N H2 ) ratio.…”

The first multidimensional view of mass loss from externally FUV irradiated protoplanetary discs

“…We use the photochemical-hydrodynamics code torus-3dpdr Bisbas et al (2015b) to run the models in this paper. In its most general form this is a coupling of the gridbased Monte Carlo radiative transfer and hydrodynamics code torus (Harries 2000;Haworth & Harries 2012;Haworth et al 2015;Harries 2015;Ali et al 2018) with the 3D photodissociation region modelling code 3d-pdr (Bisbas et al 2012) 1 .…”

“…The PDR aspect of our calculations require solving a chemical network iteratively with thermal balance (for full details see Bisbas et al 2012Bisbas et al , 2015b. The fact that the PDR calculations in 3d-pdr take place in 3D for arbitrary geometries is crucial for our models of externally photoevaporating protoplanetary discs.…”

“…The code was also validated against a series of dynamical and radiation hydrodynamic tests in Haworth & Harries (2012), Harries (2015) and Bisbas et al (2015a). The PDR components have also been checked against the Röllig et al (2007) benchmarks in Bisbas et al (2015b) The healpix scheme used by torus-3dpdr is known to work in 3D applications, however it has been modified for this work to utilize the cylindrical symmetry of our simulation grid when propagating through 3D space. To check this modified scheme we computed the UV field impinging upon a sphere embedded in a low density medium using both the 3D and 2D cylindrical scheme, ensuring that the same UV field in the sphere resulted.…”

Where can a Trappist-1 planetary system be produced?

“…It iteratively solves for the composition and temperature structure until convergence, using the approach detailed by Bisbas et al (2012Bisbas et al ( , 2015. The 33 species in the reduced network are presented in , but broadly includes atoms/ions/molecules comprised of H, He, C, O and Mg, as well as electrons, cosmic rays, PAHs and dust.…”