Similarity between the Molecular Loops in the Galactic Center and the Solar Chromospheric Arch Filaments

TL;DR

This study uses magnetohydrodynamic simulations to demonstrate that magnetic loops formed by Parker instability can explain the dense molecular loops observed in the Galactic center, showing similarities to solar chromospheric arch filaments.

Contribution

It presents a novel simulation model linking Parker instability to molecular loop formation in the Galactic center, drawing parallels with solar chromospheric structures.

Findings

Magnetic loops' length is set by the hot layer scale height (~100 pc).

Simulated velocity gradients match observations.

Loops become top-heavy with small curvature, similar to solar filaments.

Abstract

We carried out two-dimensional magnetohydrodynamic simulations of the Galactic gas disk to show that the dense loop-like structures discovered by the Galactic center molecular cloud survey by NANTEN 4 m telescope can be formed by the buoyant rise of magnetic loops due to the Parker instability. At the initial state, we assumed a gravitationally stratified disk consisting of the cool layer ($T \sim 10^3$ K), warm layer ($T \sim 10^4$ K), and hot layer ($T \sim 10^5$ K). Simulation box is a local part of the disk containing the equatorial plane. The gravitational field is approximated by that of a point mass at the galactic center. The self-gravity, and the effects of the galactic rotation are ignored. Numerical results indicate that the length of the magnetic loops emerging from the disk is determined by the scale height of the hot layer ($\sim$ 100 pc at 1 kpc from the Galactic center). The loop length, velocity gradient along the loops and large velocity dispersions at their foot points are consistent with the NANTEN observations. We also show that the loops become top-heavy when the curvature of the loop is sufficiently small, so that the rising loop accumulates the overlying gas faster than sliding it down along the loop. This mechanism is similar to that of the formation of solar chromospheric arch filaments. The molecular loops emerge from the low temperature layer just like the dark filaments observed in the H$\alpha$ image of the emerging flux region of the sun.