Reconciling the magnetic field in central disc galaxies with the dynamical mass using the cosmological simulations

TL;DR

This study uses high-resolution cosmological simulations to explore how magnetic fields in disc galaxies relate to their mass, velocity, and star formation, revealing correlations and effects of black hole feedback.

Contribution

It demonstrates the correlation between magnetic fields and galaxy properties in simulations, including the impact of black hole feedback, and compares these results with observations.

Findings

Magnetic field correlates linearly with galaxy circular velocity.

Magnetic field scales with total mass as B ~ M^{0.2}.

Black hole feedback disrupts the magnetic field-mass relation.

Abstract

The Universe is pervaded by magnetic fields in different scales, although for simplicity, they are ignored in most cosmological simulations. In this paper, we use the TNG50, which is a large cosmological galaxy formation simulation that incorporates magnetic fields with an unprecedented resolution. We study the correlation of the magnetic field with various galaxy properties such as the total, stellar and gaseous mass, circular velocity, size and star formation rate. We find a linear correlation between the average magnetic field pervading the disc of galaxies in relative isolation and their circular velocities. In addition we observed that in this sample the average magnetic field in the disc is correlated with the total mass as $\overline{B}\sim M_{\mathrm{tot,\,R_{\star}}}^{0.2}$. We also find that the massive galaxies with active wind-driven black hole feedback, do not follow this trend, as their magnetic field is substantially affected by this feedback mode in the TNG50 simulation. We show that the correlation of the magnetic field with the star formation rate is a little weaker than the circular velocity. Moreover, we compare the magnetic field components of the above sample with a compiled observational sample of non-cluster non-interacting nearby galaxies. Similar to the observation, we find a coupling between the ordered magnetic field and the circular velocity of the flat part of the rotation curve in the simulation, although contrary to the observation, the ordered component is dominant in the simulation.