3D-PDR: A new three-dimensional astrochemistry code for treating Photodissociation Regions

TL;DR

3D-PDR is a novel three-dimensional astrochemistry code that models photodissociation regions with arbitrary density distributions, improving upon previous one-dimensional models by self-consistently solving chemistry and thermal balance.

Contribution

The paper introduces 3D-PDR, a new 3D code for PDRs that handles complex geometries and radiation fields, advancing beyond traditional 1D models.

Findings

Code accurately reproduces benchmark results of 1D codes.

3D treatment can yield different results than 1D models in some cases.

Demonstrates applicability to various astrophysical cloud scenarios.

Abstract

Photodissociation regions (PDRs) define the transition zone between an ionized and a dark molecular region. They consist of neutral gas which interacts with far-ultraviolet radiation and are characterized by strong infrared line emission. Various numerical codes treating one-dimensional PDRs have been developed in the past, simulating the complexity of chemical reactions occurring and providing a better understanding of the structure of a PDR. In this paper we present the three-dimensional code, 3D-PDR, which can treat PDRs of arbitrary density distribution. The code solves the chemistry and the thermal balance self-consistently within a given three-dimensional cloud. It calculates the total heating and cooling functions at any point in a given PDR by adopting an escape probability method. It uses a HEALPix-based ray-tracing scheme to evaluate the attenuation of the far-ultraviolet radiation in the PDR and the propagation of the far-infrared/submm line emission out of the PDR. We present benchmarking results and apply 3D-PDR to i) a uniform-density spherical cloud interacting with a plane-parallel external radiation field, ii) a uniform-density spherical cloud interacting with a two-component external radiation field, and iii) a cometary globule interacting with a plane-parallel external radiation field. We find that the code is able to reproduce the benchmarking results of various other one-dimensional numerical codes treating PDRs. We also find that the accurate treatment of the radiation field in the fully three-dimensional treatment of PDRs can in some cases leads to different results when compared to a standard one-dimensional treatment.