SIMBAD references

Using a large sample of 9617 molecular clouds (MCs) from the Milky Way Imaging Scroll Painting survey, we mainly measure one-dimensional cloud-to-cloud velocity dispersions across a 450 deg² segment of the Local Arm in the Galactic second quadrant. We define the cloud-to-cloud velocity dispersion using two metrics: the standard deviation (σ_bin) and flux-weighted rms value (σ_bin,w) of the centroid velocities of ¹²CO-detected MCs within spatial bins. The typical values of σ_bin and σ_bin,w are 7.5 ± 0.5 km s^–1 and 6.2 ± 0.5 km s^–1, respectively. After categorizing clouds by sizes into three types: Type S (0.15-1.2 pc), Type M (1.2-4.8 pc), and Type L (≳4.8 pc), we find that the spatial distribution of Type S and M MCs projected onto the Galactic longitude-latitude (l-b) plane is generally uniform. Additionally, the cloud-to-cloud velocity dispersion among Type S clouds (∼7.6 and 7.4 km s^–1 for σ_bin and σ_bin,w, respectively) is systematically greater than that among Type M clouds (∼6.7 and 6.0 km s^–1 for σ_bin and σ_bin,w, respectively), with differences of 0.9-1.4 km s^–1. From these measurements, we estimate merger timescales between MCs to be approximately 0.3-0.9 Myr, which is shorter than their internal crossing timescales (∼1 Myr for Type S, ∼2 Myr for Type M, and ≳5 Myr for Type L). This disparity, particularly pronounced for larger Type L clouds, suggests that MCs are dynamically transient structures, with their gas content changing due to frequent interactions with neighboring clouds.