Arepo public version

AREPO is a massively parallel code for gravitational n-body systems and hydrodynamics, both on Newtonian as well as cosmological background. It is a flexible code that can be applied to a variety of different types of simulations, offering a number of sophisticated simulation algorithms. An description of the numerical algorithms employed by the code is given in the original code papers (Springel 2010, MNRAS, 401, 791; Pakmor et al. 2011, MNRAS, 418, 1392; Pakmor and Springel 2013, MNRAS, 432, 176; Pakmor et al. 2016, MNRAS,455,1134) and the release paper of this version (Weinberger et al. 2019).

A user guide can be found under /documentation, which also includes a 'getting started' section, which is recommended for new users. An html version of the user guide can be created using sphinx (https://www.sphinx-doc.org) by typing

cd ./documentation/
make html

and displayed by opening ./documentation/build/html/index.html.

A full version of the user guide is also available on the Arepo homepage.

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This EOS2 Version (Master's Thesis 2024)

This version of AREPO includes experimental features developed as part of a master's thesis. These features aim to extend AREPO's capabilities for modeling thermal evolution in cosmological volume simulations but require further testing and refinement to achieve a fully working implementation.

1. Experimental Thermal Evolution Models:

   • Introduced a model for effective internal energy, allowing simulation of thermal evolution with options for density-dependent (in this version for now only as a power-law threshold to keep gas from collapsing in halos in high-density regions) and time-dependent behaviors.
   • Added a new InternalEnergyOption enum:
     • NO: Default behavior.
     • CONSTANT: Fixed internal energy.
     • LINEAR: Internal energy evolves linearly with time.
     • POLYNOMIAL_PIECEWISE: A polynomial fit for time-dependent internal energy evolution.
   • Included a toggle (threshold_density) for density-dependent evolution based on CAMELS CV0 simulations.

2. Limitations and Future Work:

   • This implementation is a preliminary attempt and may not produce stable or physically accurate results.
   • Further development and validation are necessary to refine the thermal evolution models.

3. Configuration Notes:

   • This version is designed to operate with gamma close to 1 e.g., GAMMA = 1.001 (for quasi-isothermal behavior - we reset the total energy after each timestep to ensure the specific internal energy or sound speed) and non-radiative simulations pre-settings. Ensure that the configuration file (Config.sh) is updated accordingly. Then you pick your InternalEnergyOption in /src/main/allvars.c. You can change the concrete prescriptions of the model in eff_internal_energy.c. The one implemented in the code were derived from simulation outputs of CAMELS CV0 simulations https://users.flatironinstitute.org/~camels/Sims/IllustrisTNG/CV/

4. Files Added/Modified:

   • eff_internal_energy.c and eff_internal_energy.h for internal energy calculations.
   • Modifications to update_primitive_variables to integrate the experimental thermal evolution models.

For further details, refer to the thesis documentation. Users are advised to treat this version as a testing ground for experimental features.