Various radio observations have shown that the hot atmospheres of galaxy clusters are magnetized. However, our understanding of the origin of these magnetic fields, their implications on structure formation and their interplay with the dynamics of the cluster atmosphere, especially in the centres of galaxy clusters, is still very limited. In preparation for the upcoming new generation of radio telescopes (like Expanded Very Large Array, Low Wavelength Array, Low Frequency Array and Square Kilometer Array), a huge effort is being made to learn more about cosmological magnetic fields from the observational perspective. Here we present the implementation of magnetohydrodynamics (MHD) in the cosmological smoothed particle hydrodynamics (SPH) code gadget. We discuss the details of the implementation and various schemes to suppress numerical instabilities as well as regularization schemes, in the context of cosmological simulations. The performance of the SPH–MHD code is demonstrated in various one‐ and two‐dimensional test problems, which we performed with a fully, three‐dimensional set‐up to test the code under realistic circumstances. Comparing solutions obtained using athena, we find excellent agreement with our SPH–MHD implementation. Finally, we apply our SPH–MHD implementation to galaxy cluster formation within a large, cosmological box. Performing a resolution study we demonstrate the robustness of the predicted shape of the magnetic field profiles in galaxy clusters, which is in good agreement with previous studies.

Magnetic fields in the intra‐cluster medium (ICM) of galaxy clusters have been studied in the past through different methods. So far, our understanding of the origin of these magnetic fields, as well as their role in the process of structure formation and their interplay with the other constituents of the ICM, is still limited. In the coming years, the up‐coming generation of radio telescopes is going to provide new data that will have the potential of setting constraints on the properties of magnetic fields in galaxy clusters. Here, we present zoomed‐in simulations for a set of massive galaxy clusters (Mv ≥ 1015 h−1 M⊙). This is an ideal sample to study the evolution of the magnetic field during the process of structure formation in detail. Turbulent motions of the gas within the ICM will manifest themselves in a macroscopic magnetic resistivity ηm, which has to be taken explicitly into account, especially at scales below the resolution limit. We have adapted the magnetohydrodynamic (MHD) gadget code by Dolag & Stasyszyn to include the treatment of the magnetic resistivity, and for the first time we have included non‐ideal MHD equations to better follow the evolution of the magnetic field within the galaxy clusters. We investigate which value of the magnetic resistivity ηm is required to match the magnetic field profile derived from radio observations. We find that a value of ηm∼ 6 × 1027 cm2 s−1 is necessary to recover the shape of the magnetic field profile inferred from radio observations of the Coma cluster. This value agrees well with the expected level of turbulent motions within the ICM at our resolution limit. The magnetic field profiles of the simulated clusters can be fitted by a β‐model‐like profile, with small dispersion of the parameters. We also find that the temperature, density and entropy profiles of the clusters depend on the magnetic resistivity constant, having flatter profiles in the inner regions when the magnetic resistivity increases.

We study the alignments between the angular momentum of individual objects and the largescale structure in cosmological numerical simulations and real data from the Sloan Digital Sky Survey, Data Release 6 (SDSS-DR6). To this end, we measure anisotropies in the two point cross-correlation function around simulated haloes and observed galaxies, studying separately the one-and two-halo regimes. The alignment of the angular momentum of dark-matter haloes in cold dark matter ( CDM) simulations is found to be dependent on scale and halo mass. At large distances (two-halo regime), the spins of high-mass haloes are preferentially oriented in the direction perpendicular to the distribution of matter; lower mass systems show a weaker trend that may even reverse to show an angular momentum in the plane of the matter distribution. In the one-halo term regime, the angular momentum is aligned in the direction perpendicular to the matter distribution; the effect is stronger than for the one-halo term and increases for higher mass systems.On the observational side, we focus our study on galaxies in the SDSS-DR6 with elongated apparent shapes, and study alignments with respect to the major semi-axis. We study five samples of edge-on galaxies; the full SDSS-DR6 edge-on sample, bright galaxies, faint galaxies, red galaxies and blue galaxies (the latter two consisting mainly of ellipticals and spirals, respectively). Using the two-halo term of the projected correlation function, we find an excess of structure in the direction of the major semi-axis for all samples; the red sample shows the highest alignment (2.7 ± 0.8 per cent) and indicates that the angular momentum of flattened spheroidals tends to be perpendicular to the large-scale structure. These results are in qualitative agreement with the numerical simulation results indicating that the angular momentum of galaxies could be built up as in the Tidal Torque scenario. The one-halo term only shows a significant alignment for blue spirals (1.0 ± 0.4 per cent), consistent with the one-halo results from the simulation but with a lower amplitude. This could indicate that even though the structure traced by galaxies is adequate to study large-scale structure alignments, this would not be the case for the inner structure of low-mass haloes, M ≤ 10 13 h −1 M , an effect apparently more important around red g − r > 0.7 galaxies.