SPARCS -- combining radiation hydrodynamics with non-equilibrium metal chemistry in the SWIFT astrophysical code

TL;DR

SPARCS is a new astrophysical simulation tool that combines radiation hydrodynamics with non-equilibrium metal chemistry, enabling detailed on-the-fly modeling of ionization, radiation pressure, and emission in complex interstellar environments.

Contribution

It integrates multi-frequency UV radiative transfer with non-equilibrium metal chemistry in the SWIFT code, validated against analytic solutions and standard photo-ionization codes.

Findings

Non-equilibrium effects can increase low ion fractions by up to an order of magnitude.

SPARCS accurately models ionization fronts in inhomogeneous media.

Simulations produce realistic optical emission line observations.

Abstract

We present SPARCS, which combines the moment-based radiative transfer method SPH-M1RT with the non-equilibrium metal chemistry solver CHIMES in the modern highly-parallel astrophysical code SWIFT. SPARCS enables on-the-fly radiation hydrodynamics simulations, with multi-frequency ultraviolet radiative transfer coupled with all ionisation states of 11 major elements, in the presence of dust, cosmic ray ionization and heating, and self-gravity. Direct radiation pressure on gas and dust is also accounted for. We validate SPARCS against analytic solutions and standard photo-ionization codes such as CLOUDY in idealized tests. As an example application, we simulate an ionization front propagating through an inhomogeneous interstellar medium with solar metallicity. We produce mock optical emission line observations with the level population calculation code HyLight and the diagnostic radiative transfer code RADMC3D. We find that non-equilibrium effects and inhomogeneities can boost the low ion fractions by up to an order of magnitude. Possible applications of SPARCS include studying the dynamical impact of radiation on gas in star-forming regions, and in the interstellar and circumgalactic medium, as well as interpreting line diagnostics in such environments, and galactic or AGN outflows.