| Summary: | According to the structures traced by ^13 CO spectral lines within ^12 CO molecular clouds (MCs), we investigate the contributions of their internal gas motions and relative motions to the total velocity dispersions of ^12 CO MCs. Our samples of 2851 ^12 CO MCs harbor a total of 9556 individual ^13 CO structures, among which 1848 MCs (∼65%) have one individual ^13 CO structure and the other 1003 MCs (∼35%) have multiple ^13 CO structures. We find that the contribution of the relative motion between ^13 CO structures ( ${\sigma }_{{}^{13}\mathrm{CO},\mathrm{re}}$ ) is larger than that from their internal gas motion ( ${\sigma }_{{}^{13}\mathrm{CO},\mathrm{in}}$ ) in ∼62% of 1003 MCs in the “Multiple” regime. In addition, we find that ${\sigma }_{{}^{13}\mathrm{CO},\mathrm{re}}$ tends to increase with the total velocity dispersion ( ${\sigma }_{{}^{12}\mathrm{CO},\mathrm{tot}}$ ) in our samples, especially for MCs with multiple ^13 CO structures. This result provides a manifestation of macroturbulence within MCs, which gradually becomes the dominant way of storing kinetic energy along with the development of MC scales.
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