Chemistry

Feedback mechanisms such as supernova feedback transfer metals to the nearby gas particles. There is no mass exchange (mass advection) in SPH methods, as in grid-based or moving-mesh hydrodynamics solvers. As a result, the metals received by the gas particles are locked in these particles. Grid or moving-mesh codes have mass advection and often implement passive scalar advection of metals to model metal mixing. GEAR implements different methods to model metal mixing.

Smoothed metallicity

The smoothed metallicity scheme consists in using the SPH to smooth the metallicity of each particle over the neighbors. It is worth to point the fact that we are not exchanging any metals but only smoothing it. The parameter GEARChemistry:initial_metallicity set the (non smoothed) initial mass fraction of each element for all the particles and GEARChemistry:scale_initial_metallicity use the feedback table to scale the initial metallicity of each element according the Sun’s composition. If GEARChemistry:initial_metallicity is negative, then the metallicities are read from the initial conditions.

For this chemistry scheme the parameters are:

GEARChemistry:
 initial_metallicity: 1         # Initial metallicity of the gas (mass fraction)
 scale_initial_metallicity: 1   # Should we scale the initial metallicity with the solar one?