Recently, the Milky Way Imaging  Scroll Painting (MWISP) survey group members of Purple Mountain  Observatory of CAS, using the Delingha 13.7m millimeter wave telescope,  first revealed the relatively complete molecular structure of the Outer  Arm in the second galactic quadrant. The result is shown in Fig. 1. This  work will soon be published in The Astrophysical Journal Supplement  Series. 

  Outer arm is a major spiral  arm of the Milky Way. At the second galactic quadrant, its distance to  us is about 5-7 kpc, namely about 16,000-23,000 light year. Because of  its further distance, the molecular emissions of the arm are so weak  that the past survey could only detect a few bright ones. But today,  using the Delingha 13.7m millimeter wave telescope, the MWISP group have  detected 457 Outer arm molecular clouds in the region of galactic  longitude from 100° to 150° and galactic latitude from -3° to 5°.  Among them, 332 (about 69%) are newly detected. The total mass of the  detected Outer arm clouds is more than 3,000,000 solar mass. 

  The on-going MWISP project is  the world’s highest sensitivity large scale no-bias CO molecular  spectral line survey. This project has helped us achieving many progress  about the Milky Way structure, such as the discovery of the new spiral  arm reported in 2015 (Sun et al. 2015). As the survey carrying on, more  secrets about the Milky Way structure will be gradually revealed. 

By DU Xinyu

   Fig.1. The Milky Way plan view. The red circles  are the Outer arm molecular clouds. The red dashed curve indicates the  fitting result of the Outer arm. And the red solid curve indicates the  translationally moved result by taking the fitting result from Reid et  al.           (2014) into account.

  The article link：http://arxiv.org/abs/1602.08229