Chemulator: Fast, accurate thermochemistry for dynamical models through emulation

Springer Link (Chiba Institute of Technology)

Abstract

Context. Chemical modelling serves two purposes in dynamical models: accounting for the effect of microphysics on the dynamics and providing observable signatures. Ideally, the former must be done as part of the hydrodynamic simulation but this comes with a prohibitive computational cost that leads to many simplifications being used in practice.\n\n\n\nAims. We aim to produce a statistical emulator that replicates a full chemical model capable of solving the temperature and abundances of a gas through time. This emulator should suffer only a minor loss of accuracy when compared to a full chemical solver and would have a fraction of the computational cost allowing it to be included in a dynamical model.\n\n\n\nMethods. The gas-grain chemical code UCLCHEM was updated to include heating and cooling processes, and a large dataset of model outputs from possible starting conditions was produced. A neural network was then trained to map directly from inputs to outputs.\n\n\n\nResults. Chemulator replicates the outputs of UCLCHEM with an overall mean squared error (MSE) of 1.7 × 10−4 for a single time step of 1000 yr, and it is shown to be stable over 1000 iterations with an MSE of 3 × 10−3 on the log-scaled temperature after one timzze step and 6 × 10−3 after 1000 time steps. Chemulator was found to be approximately 50 000 times faster than the time-dependent model it emulates but can introduce a significant error to some models.

Authors 4

1. Jonathan Holdship Aachen Leiden Observatory

   Leiden University · Leiden Observatory · University College London

   Affiliation as printed

   Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, UK

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

2. S. Viti Aachen Leiden Observatory

   Leiden University · Leiden Observatory · University College London

   Affiliation as printed

   Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, UK

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

3. Thomas J. Haworth

   Queen Mary University of London

   Affiliation as printed

   Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK

4. John D. Ilee

   University of Leeds

   Affiliation as printed

   School of Physics & Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK