An Outer Arm in the Second Galactic Quadrant: Structure
  The lack of arm tracers, especially the remote tracers, is one of the most
difficult problems preventing us from studying the structure of the Milky Way.
Fortunately, with its high-sensitivity CO survey, the Milky Way Imaging Scroll
Painting (MWISP) project offers such an opportunity. Since completing about
one-third of its mission, an area of l=[100,150] deg, b=[-3,5] deg has nearly
been covered. The Outer arm of the Milky Way first clearly revealed its shape
in the second galactic quadrant in the form of molecular gas --- this is the
first time that the Outer arm has been reported in such a large-scale mapping
of molecular gas. Using the 115 GHz 12CO(1-0) data of MWISP at the LSR velocity
~= [-100,-60] km s^-1 and in the area mentioned above, we have detected 481
molecular clouds in total, and among them 332 (about 69\%) are newly detected
and 457 probably belong to the Outer arm. The total mass of the detected Outer
arm clouds is ~ 3.1*10^6 M_sun. Assuming that the spiral arm is a logarithmic
spiral, the pitch angle is fitted as ~ 13.1 deg. Besides combining both the CO
data from MWISP and the 21 cm HI data from the Canadian Galactic Plane Survey
(CGPS), the gas distribution, warp, and thickness of the Outer arm are also
studied.
