Abstract
In ISM simulations, pre-computed tables have typically been used to account for the metal contribution to the total cooling. This has been the preferred method as it is computationally inexpensive, but tables rely on a range of assumptions, such as collisional equilibrium and often zero radiation. In this work, we aim at investigating how an improved metal cooling implementation would affect the results of ISM simulations. To this goal, we run simulations with the radiation hydrodynamical solver kramses-rt, a customized version of ramses-rt where a chemical network generated by krome has been included. Simulations are conducted with three versions of the code, where we implemented different approaches to account for metal cooling: (1) interpolation of a collisional ionization equilibrium table, pre-computed with cloudy in a medium with no radiation (CIE model); (2) the Gnedin & Hollon cooling and heating functions, based on pre-computed tables designed to account for the local radiation field (GH model); (3) an expanded chemical network including CI, CII, SiI, SiII, SiIII, OI and OII, where the metal cooling function is computed on the fly based on local cell properties (CSO model). We conducted one-zone simulations with and without radiation, 1d simulations with different radiation spectra, and 3d simulations of a star at the center of a turbulent molecular medium. In our one zone simulations, we observe (for typical HII region conditions) a decrease in cooling for the GH model compared to the other two implementations. For PDR conditions, we see that the GH and CSO models result in larger total cooling compared to the CIE model. From the dynamical 1d simulations, after 3 Myr, we see that the temperature in the GH model is the largest close to the star (T ≃ 105−6 K), but the temperatures are lower than other models in the rest of the HII region, resulting is a ≃ 10% decrease in HII region radius. The PDR in the GH and CSO models have reduced size compared to the CIE model, with the largest discrepancies being 0.56 × ∆PDR,CIE and 0.58 × ∆PDR,CIE, for initial densities n = 10 cm−3 and n = 1 cm−3 . 3d simulations show that the HII region in the CSO and GH models have volumes 1.15×VHII,CIE and 0.74×VHII,CIE respectively. The PDR volume is smaller for the CSO and GH models compared to the CIE model, being 0.716×VPDR,CIE and 0.487×VPDR,CIE respectively, with the volume VHII+VPDR always the largest for the CIE model. Finally, the Kennicutt-Schmidt relation has been applied to estimate the total star formation rate (SFR) in the box. At t = 3 Myr we found that the CSO and GH models have SFR about 3% larger than the CIE model.
Supervisor:
Professor Sijing Shen, Institute of Theoretical Astrophysics, UiO
Postdoctoral Fellow Davide Decataldo, Institute of Theoretical Astrophysics, UiO
Intern. assessor: Professor Øystein Elgarøy, Institute of Theoretical Astrophysics, UiO
Extern. assessor: Astrophysicist and Science Communicator Peter Laursen, University of Copenhagen