Discovery of Molecular Loop 3 in the Galactic Center: Evidence for a
  Positive-Velocity Magnetically Floated Loop towards $L=355^\circ-359^\circ$
  We have discovered a molecular dome-like feature towards $355^{\circ} \leq l
\leq 359^{\circ}$ and $0^{\circ} \leq b \leq 2^{\circ}$. The large velocity
dispersions of 50--100 km s$^{-1}$ of this feature are much larger than those
in the Galactic disk and indicate that the feature is located in the Galactic
center, probably within $\sim1$ kpc of Sgr A$^{*}$. The distribution has a
projected length of $\sim600$ pc and height of $\sim300$ pc from the Galactic
disk and shows a large-scale monotonic velocity gradient of $\sim130$ km s
$^{-1}$ per $\sim600$ pc. The feature is also associated with HI gas having a
more continuous spatial and velocity distribution than that of $^{12}$CO. We
interpret the feature as a magnetically floated loop similar to loops 1 and 2
and name it "loop 3". Loop 3 is similar to loops 1 and 2 in its height and
length but is different from loops 1 and 2 in that the inner part of loop 3 is
filled with molecular emission. We have identified two foot points at the both
ends of loop 3. HI, $^{12}$CO and $^{13}$CO datasets were used to estimate the
total mass and kinetic energy of loop 3 to be $\sim3.0 \times 10^{6} \Mo$ and
$\sim1.7 \times 10^{52}$ ergs. The huge size, velocity dispersions and energy
are consistent with the magnetic origin the Parker instability as in case of
loops 1 and 2 but is difficult to be explained by multiple stellar explosions.
We argue that loop 3 is in an earlier evolutionary phase than loops 1 and 2
based on the inner-filled morphology and the relative weakness of the foot
points. This discovery indicates that the western part of the nuclear gas disk
of $\sim1$ kpc radius is dominated by the three well-developed magnetically
floated loops and suggests that the dynamics of the nuclear gas disk is
strongly affected by the magnetic instabilities.
