Modeling Photoionized Turbulent Material in the Circumgalactic Medium III: Effects of Co-rotation and Magnetic Fields

TL;DR

This study uses hydrodynamic and MHD simulations to explore how magnetic fields and rotation influence the multiphase, turbulent circumgalactic medium around Milky Way-like galaxies over billions of years.

Contribution

It provides new insights into the effects of magnetic fields and rotation on the thermal structure and angular momentum distribution in the CGM through detailed simulations.

Findings

Magnetic fields lead to a hotter CGM with central cool gas dominated by magnetic pressure.

Non-MHD runs produce more cold clouds and low angular momentum filaments.

Similar ion ratios are found in both MHD and non-MHD simulations, differing from equilibrium predictions.

Abstract

Absorption-line measurements of the circumgalactic medium (CGM) display a highly non-uniform distribution of lower ionization state species accompanied by more widespread higher ionization state material. This suggests that the CGM is a dynamic, multiphase medium, such as arises in the presence of turbulence. To better understand this evolution, we perform hydrodynamic and magneto-hydrodynamic (MHD) simulations of the CGM surrounding Milky Way-like galaxies. In both cases, the CGM is initially in hydrostatic balance in a $10^{12}$ solar masses dark matter gravitational potential, and the simulations include rotation in the inner halo and turbulence that decreases radially. They also track ionizations, recombinations, and species-by-species radiative cooling in the presence of the redshift-zero UV background, employing the MAIHEM non-equilibrium chemistry package. We find that after 9 Gyrs of evolution, the presence of a magnetic field leads to an overall hotter CGM, with cool gas in the center where magnetic pressure dominates. While the non-MHD run produces more cold clouds overall, we find similar Si IV/O VI and N V/O VI ratios between the MHD and non-MHD runs, which are both very different from their equilibrium values. The non-MHD halo develops cool, low angular momentum filaments above the central disk, in comparison to the MHD run that has more efficient angular momentum transport, especially for the cold gas which forms a more ordered and extended disk late into its evolution.