Periodic Reporting for period 4 - CRAGSMAN (The Impact of Cosmic Rays on Galaxy and Cluster Formation)
Okres sprawozdawczy: 2020-04-01 do 2021-03-31
Exploring the impact of cosmic rays on galaxy formation. We have implemented the physics of cosmic rays in the cosmological moving-mesh code Arepo and self-consistently simulated the injection of cosmic rays at supernova shocks, following cosmic-ray propagation in the interstellar medium, in galaxies and in the large-scale structure of the Universe. We simulated the effects of cosmic rays on the formation of Milky Way-mass galaxies in a cosmological context and find that global properties such as stellar mass and star formation rate vary little between simulations with various CR transport physics, whereas structural properties such as disc sizes, circum-galactic medium densities or temperatures can be strongly affected.
Galactic magnetism - formation and dynamical impact on galaxies. High redshift, massive halos are observed to have sustained, high star formation rates, which require that the amount of cold gas in the halo is continuously replenished. Supersonic, cold streams could deliver the required high accretion rates but they should break up due to hydrodynamic instabilities. We find that magnetic fields can allow streams to survive much longer and to reach the inner galaxy.
Formation and evolution of galaxy clusters. We have implemented an improved model for relativistic jets from active galactic nuclei at the centres of galaxy clusters and studied magnetic amplification, cosmic-ray transport and heating of the cooling dense intra-cluster medium. The simulations explain recent observations of the Sunyaev-Zel'dovich effect and turbulently broadened X-ray lines.
Non-thermal signatures of galaxies and clusters. We developed efficient methods to follow cosmic ray electron and proton spectra in three-dimensional simulations of galaxy formation. A first application to the evolution of CR electron spectra in supernova explosions reveals a number of surprising findings on the electron acceleration efficiency and questions our current paradigm of diffusive shock acceleration.
We have implemented the equations for Braginskii magneto-hydrodynamics in the moving-mesh code Arepo and are studying the physics of weakly collisional plasmas in cosmological galaxy cluster simulations. We have developed efficient code for particle-in-cell simulations to study kinetic plasma physics of the cosmic ray streaming instability, which will enable to construct improved closure schemes for our new Alfvén-wave regulated cosmic ray hydrodynamics, which are based on coarse-grained kinetic plasma simulations. Performing global dynamical simulations in the context of the interstellar, circum-galactic, and intra-cluster medium with these novel sub-grid approaches and comparing the results to observations enables us to obtain a direct feedback on how these schemes perform in large-scale simulations and a fast turnaround in case there are discrepancies. If successful, this could pave the road for a new influential approach to computational astrophysics in the context of galaxy and cluster formation.
We have substantiated our original hypothesis that cosmic rays can actively modify the morphologies of galaxies and drive powerful outflows. At the scales of galaxy clusters, we confirmed that cosmic-ray heating can balance the fast radiative cooling at the centres of cooling galaxy clusters, thus mitigate star formation. Thus, cosmic ray feedback could be one of the key processes that regulates and governs galaxy formation. At the same time, this novel implementation enabled us to simulate non-thermal signatures of live galaxy models at radio and gamma-ray energies, thus discovering the cause of two fundamental relations of galaxies, the far-infrared--gamma-ray and far-infrared--radio correlations.