MHD Simulation in Galactic Center Region with Radiative Cooling and Heating

TL;DR

This study uses 3D MHD simulations to explore how magnetic fields influence gas dynamics in the galactic bulge, highlighting the effects of radiative cooling and heating on magnetic field amplification and structure formation.

Contribution

It demonstrates that radiative cooling and heating lead to magnetically dominated regions and affect the vertical gas distribution, providing new insights into magnetic influence in galactic bulge dynamics.

Findings

Magnetic fields reach several hundred microGauss locally.

Magnetically dominated mid-latitude regions form due to radiative effects.

Vertical thickness of gas regions matches observed neutral atomic gas distribution.

Abstract

We investigate the role of magnetic field on the gas dynamics in a galactic bulge region by three dimensional simulations with radiative cooling and heating. While high-temperature corona with $T>10^6\ {\rm K}$ is formed in the halo regions, the temperature near the mid-plane is $\lesssim 10^4\ {\rm K}$ following the thermal equilibrium curve determined by the radiative cooling and heating. Although the thermal energy of the interstellar gas is lost by radiative cooling, the saturation level of the magnetic field strength does not significantly depend on the radiative cooling and heating. The magnetic field strength is amplified to $10\ {\rm \mu G}$ on average, and reaches several hundred ${\rm \mu G}$ locally. We find the formation of magnetically dominated regions at mid-latitudes in the case with the radiative cooling and heating, which is not seen in the case without radiative effect. The vertical thickness of the mid-latitude regions is $50-150\ {\rm pc}$ at the radial location of $0.4-0.8\ {\rm kpc}$ from the galactic center, which is comparable to the observed vertical distribution of neutral atomic gas. When we take the average of different components of energy density integrated over the galactic bulge region, the magnetic energy is comparable to the thermal energy. We conclude that the magnetic field plays a substantial role in controlling the dynamical and thermal properties of the galactic bulge region.