A chemical model for the interstellar medium in galaxies

¹ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
e-mail: stefano.bovino@uni-hamburg.de
² Centre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen, Denmark
³ Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
⁴ Departamento de Astronomía, Facultad Ciencias Físicas y Matemáticas, Universidad de Concepción, Av. Esteban Iturra s/n Barrio Universitario, Casilla 160, Concepción, Chile

Received: 19 January 2016
Accepted: 15 February 2016

Abstract

Aims. We present and test chemical models for three-dimensional hydrodynamical simulations of galaxies. We explore the effect of changing key parameters such as metallicity, radiation, and non-equilibrium versus equilibrium metal cooling approximations on the transition between the gas phases in the interstellar medium.

Methods. The microphysics was modelled by employing the public chemistry package KROME, and the chemical networks were tested to work in a wide range of densities and temperatures. We describe a simple H/He network following the formation of H₂ and a more sophisticated network that includes metals. Photochemistry, thermal processes, and different prescriptions for the H₂ catalysis on dust are presented and tested within a one-zone framework. The resulting network is made publicly available on the KROME webpage.

Results. We find that employing an accurate treatment of the dust-related processes induces a faster HI–H₂ transition. In addition, we show when the equilibrium assumption for metal cooling holds and how a non-equilibrium approach affects the thermal evolution of the gas and the HII–HI transition.

Conclusions. These models can be employed in any hydrodynamical code via an interface to KROME and can be applied to different problems including isolated galaxies, cosmological simulations of galaxy formation and evolution, supernova explosions in molecular clouds, and the modelling of star-forming regions. The metal network can be used for a comparison with observational data of CII 158 μm emission both for high-redshift and for local galaxies.