Combining HI data from the Canadian Galactic Plane Survey ( CGPS ) and CO data from the Milky Way Imaging Scroll Painting ( MWISP ) project , we have identified a new segment of a spiral arm between Galactocentric radii of 15 and 19 kpc that apparently lies beyond the Outer Arm in the second Galactic quadrant .
Over most of its length , the arm is 400-600 pc thick in z .
The new arm appears to be the extension of the distant arm recently discovered by Dame & Thaddeus ( 9 ) as well as the Scutum - Centaurus Arm into the outer second quadrant .
Our current survey identified a total of 72 molecular clouds with masses on the order of 10 ^ { 2 } -10 ^ { 4 } M _ { \sun } that probably lie in the new arm .
When all of the available data from the CO molecular clouds are fit , the best - fitting spiral model gives a pitch angle of 9.3 ^ { \circ } \pm 0.7 ^ { \circ } .