Magnetic fields during galaxy mergers

TL;DR

This study uses 3D magneto-hydrodynamical simulations to explore how magnetic fields evolve during galaxy mergers, revealing peaks in magnetic strength linked to geometrical effects and density enhancements.

Contribution

First grid-based 3D MHD simulations of magnetic field evolution during galaxy mergers without stellar feedback or dark matter components.

Findings

Magnetic field strength peaks at 5 and 25 kpc scales during mergers.

Outer region peaks are due to geometrical effects of galaxy overlap.

Central magnetic field enhancement correlates with density increase.

Abstract

Galaxy mergers are expected to play a central role for the evolution of galaxies, and may have a strong impact on their magnetic fields. We present the first grid-based 3D magneto-hydrodynamical simulations investigating the evolution of magnetic fields during merger events. For this purpose, we employ a simplified model considering the merger event of magnetized gaseous disks in the absence of stellar feedback and without a stellar or dark matter component. We show that our model naturally leads to the production of two peaks in the evolution of the average magnetic field strength within 5 kpc, within 25 kpc and on scales in between 5 and 25 kpc. The latter is consistent with the peak in the magnetic field strength reported by Drzazga et al. (2011) in a merger sequence of observed galaxies. We show that the peak on the galactic scale and in the outer regions is likely due to geometrical effects, as the core of one galaxy enters the outskirts of the other one. In addition, there is a physical enhancement of the magnetic field within the central ~5 kpc, reflecting the enhancement in density due to efficient angular momentum transport. We conclude that high-resolution observations of the central regions will be particularly relevant to probe the evolution of magnetic field structures during merger events.