On the Spatial Distribution of 13CO Structures within 12CO Molecular Clouds

Abstract

We look into the 2851 ^12 CO molecular clouds harboring ^13 CO structures to reveal the distribution of the projected angular separations and radial velocity separations between their internal ^13 CO structures. The projected angular separations are determined using the minimal spanning tree algorithm. We find that ∼50% of the angular separations fall in a narrow range of ∼3′–7′ with a median of ∼5′, and the corresponding radial velocity separations mainly range from ∼0.3 to 2.5 km s ^−1 . The mean and standard deviation of the angular separations of the internal ^13 CO structures within ^12 CO clouds appear to be universal, independent of the ^12 CO cloud angular areas and the counts of their internal ^13 CO structures. We also reveal a scaling relation between the ^12 CO cloud angular area and its harbored ^13 CO structure count. These results suggest there is a preferred angular separation between ^13 CO structures in these ^12 CO clouds, considering the distance effects. According to that, we propose an alternative picture for the assembly and destruction of molecular clouds: there is a fundamental separation for the internal structures of molecular clouds, the build-up and destruction of molecular clouds proceeds under this fundamental unit.

Keywords

• Interstellar medium
• Interstellar molecules
• Molecular clouds