Nobeyama 45 m Local Spur CO survey. I. Giant molecular filaments and cluster formation in the Vulpecula OB association

Abstract: We have performed new large-scale $^{12}$CO, $^{13}$CO, and C$^{18}$O $J=$1-0 observations toward the Vulpecula OB association ($l \sim 60^\circ$) as part of the Nobeyama 45 m Local Spur CO survey project. Molecular clouds are distributed over $\sim 100$ pc, with local peaks at the Sh 2-86, Sh 2-87, and Sh 2-88 high-mass star-forming regions in the Vulpecula complex. The molecular gas is associated with the Local Spur, which corresponds to the nearest inter-arm region located between the Local Arm and the Sagittarius Arm. We discovered new giant molecular filaments (GMFs) in Sh 2-86, with a length of $\sim 30$ pc, width of $\sim 5$ pc, and molecular mass of $\sim 4\times 10^4\ M_{\odot}$. We also found that Sh 2-86 contains the three velocity components at 22, 27, and 33 km s$^{-1}$. These clouds and GMFs are likely to be physically associated with Sh 2-86 because they have high $^{12}$CO $J =$ 2-1 to $J =$ 1-0 intensity ratios and coincide with the infrared dust emission. The open cluster NGC 6823 exists at the common intersection of these clouds. We argue that the multiple cloud interaction scenario, including GMFs, can explain cluster formation in the Vulpecula OB association.