A Possible Extension of the Scutum-Centaurus Arm into the Outer Second Quadrant--Purple Mountain Observatory

A Possible Extension of the Scutum-Centaurus Arm into the Outer Second Quadrant

The Milky Way Imaging Scroll Painting (MWISP) group of Purple Mountain Observatory (PMO) identified a new segment of a spiral arm in the second Galactic quadrant~(Figure 1). This arm with Galactocentric radii of 15 and 19 kpc that apparently lies beyond the Outer Arm, is the outermost arm so far. Over most of its length, the arm is 400-600 pc thick in Z. Using the 13.7-m telescope of the PMO in Delingha, China, the MWISP group conducted CO observation.

By with SUN Yan

Fig. 1 Latitude–velocity diagrams of CO (image) and Hi (contours)integrated in l from 127 to 132. The dashed box indicates the approximate boundaries of the outermost feature. The contour levels are 35, 75, 100, 150, and 200 K. The Outer Arm and the outermost feature are clearly seen as strong,separate features.

The current survey identified a total of 72 molecular clouds with masses on the order of 100-10000 solar mass that probably lie in the new arm. Researchers of Harvard-Smithsonian Center for Astrophysics (CfA) identified a new segment of aspiral arm that appears to be the extension of the Scutum-Centaurus Arm in the first Galactic quadrant. This newly identified arm might be the extension of the distant arm recently discovered by Dame & Thaddeus (2011) as well as the Scutum-Centaurus Arm into the outer second quadrant. This paper has been accepted for publication in the Astrophysical Journal Letters.