Discovery of the Pigtail Molecular Cloud in the Galactic Center

The Astrophysical Journal (Impact Factor: 5.99). 09/2012; 756(1):87. DOI: 10.1088/0004-637X/756/1/87
Source: arXiv


This paper reports the discovery of a helical molecular cloud in the central
molecular zone (CMZ) of our Galaxy. This "pigtail" molecular cloud appears at
(l, b, V_LSR) ~ (-0.7deg, +0.0deg, -70 to -30 km/s), with a spatial size of ~
(20 pc)^2 and a mass of (2-6) 10^5 solar masses. This is the third helical
gaseous nebula found in the Galactic center region to date. Line intensity
ratios indicate that the pigtail molecular cloud has slightly higher
temperature and/or density than the other normal clouds in the CMZ. We also
found a high-velocity wing emission near the footpoint of this cloud. We
propose a formation model of the pigtail molecular cloud. It might be
associated with a magnetic tube that is twisted and coiled because of the
interaction between clouds in the innermost x_1 orbit and ones in the outermost
x_2 orbit.

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Available from: Tetsuo Hasegawa,
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    ABSTRACT: We report the results of millimeter-wave molecular line observations of the Tornado Nebula (G357.7--0.1), which is a bright radio source behind the Galactic Center region. A 15'x15' area was mapped in the J=1--0 lines of CO, 13CO, and HCO+ with the Nobeyama Radio Observatory 45-m telescope. The VLA archival data of OH at 1720 MHz were also reanalyzed. We found two molecular clouds with separate velocities, V_LSR=-14 km/s and +5 km/s. These clouds show rough spatial anti-correlation. Both clouds are associated with OH 1720 MHz emissions in the area overlapping with the Tornado Nebula. The spatial and velocity coincidence indicates violent interaction between the clouds and the Tornado nebula. Modestly excited gas prefers the position of the Tornado "head" in the -14 km/s cloud, also suggesting the interaction. Virial analysis shows that the +5 km/s cloud is more tightly bound by self-gravity than the -14 km/s cloud. We propose a formation scenario for the Tornado Nebula; the +5 km/s cloud collided into the -14 km/s cloud, generating a high-density layer behind the shock front, which activates a putative compact object by Bondi-Hoyle-Lyttleton accretion to eject a pair of bipolar jets.
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