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We carried out two-dimensional magnetohydrodynamic simulations of theGalactic gas disk to show that the dense loop-like structures discovered by theGalactic center molecular cloud survey by NANTEN 4 m telescope can be formed bythe buoyant rise of magnetic loops due to the Parker instability. At theinitial state, we assumed a gravitationally stratified disk consisting of thecool 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 theequatorial plane. The gravitational field is approximated by that of a pointmass at the galactic center. The self-gravity, and the effects of the galacticrotation are ignored. Numerical results indicate that the length of themagnetic loops emerging from the disk is determined by the scale height of thehot 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 footpoints are consistent with the NANTEN observations. We also show that the loopsbecome top-heavy when the curvature of the loop is sufficiently small, so thatthe rising loop accumulates the overlying gas faster than sliding it down alongthe loop. This mechanism is similar to that of the formation of solarchromospheric arch filaments. The molecular loops emerge from the lowtemperature layer just like the dark filaments observed in the H$\alpha$ imageof the emerging flux region of the sun.

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