A Detailed Observational Study of Molecular Loops 1 and 2 in the Galactic Center
Fukui et al. (2006) discovered two molecular loops in the Galactic center that are likely created by the magnetic flotation due to the Parker instability with an estimated field strength of ∼150 µG. Following the discovery, we present here a detailed study of the two loops based on NANTEN 12 CO(J=1–0) and 13 CO(J=1–0) datasets. The two loops are located in l = 355 ◦ – 359 ◦ and b = 0 ◦ – 2 ◦ at a velocity range of -20 – -180 km s −1 . They have a projected total length of ∼ 600 pc and heights of ∼250 – 300 pc from the Galactic disk at a distance of 8.5 kpc. They have loop-like filamentary distributions of 30 pc width and show bright foot points in the 12 CO emission in the edges of the loops at b ∼ 0.8 ◦ – 1.0 ◦ . These foot points are characterized by velocity dispersions of 50 – 100 km s −1 , much larger than those in the Galactic disk, supporting that the loops are located in the Galactic center within ∼1 kpc of Sgr A*. The loops also show large-scale velocity gradients of ∼30 – 50 km s −1 per ∼100 pc. We present an attempt to determine geometrical parameters and velocities of the loops by assuming that the loops having the same size are expanding and rotating at a constant radius R. The analysis yields that the loops are rotating at 50 km s −1 and expanding at 150 km s −1 at a radius of 670 pc from the center.