PIERNIK (Hanasz et al. 2010a, 2010b, 2012a, 2012b) is a grid-based multi-fluid magneto-hydrodynamical (MHD) code, using conservative numerical schemes, and developped in Torun, Poland. It includes thermal gas with cooling and heating, N-body particles for stars and dark matter, Adaptive Mesh Refinement (AMR), as well as a star formation and feedback module based on sink particles. Furthermore, PIERNIK allows Cosmic Rays to be modeled as a separate fluid, with different modules evolving protons, moment-dependent propagation of electrons, as well as secondary cosmic rays. More details can be found on the PIERNIK webpage.
During my time in Poland, as well as for my project on Milky Way nuclear winds in Italy, I developed several key modules and aspects of the PIERNIK code needed for my simulations:
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The N-body particle module, based on the particle-Mesh method and projecting particles onto the grid using the Triangular Shaped Clouds, while evolving them with the leapfrog time-integration scheme. This was necessary to model live stars and dark matter components of galaxies in my models, and to evolve sink particles required for the star formation module.
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The cooling part of the thermal module, using an exact integration scheme (Townsend 2009). This was necessary to model thermal gas in my simulations, and thermal supernova feedback.
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The star formation and feedback module. Sink particles accrete star forming gas, until they reach a maximum mass threshold (typically 100 solar masses), after which they trigger supernova explosions, releasing energy into the neighboring cells. The feedback is physically motivated, following Kim & Ostriker (2017), with a combination of thermal and kinetic energy being injected depending on whether the Sedov phase is resolved.
- The Galactic Center setup. Using a state-of the art rotating Galactic gravitational potential fine-tuned for the Galactic Center (Hunter et al. 2024), AMR to reach a resolution of 3 pc in the central part, and accurate photo-electric heating from UV sources and cosmic rays, I managed to re-create a fully self-consistent model of the Milky Way Central Molecular Zone.