Molecular Environments of 51 Planck Cold Clumps in the Orion Complex

A mapping survey of 51 Planck cold clumps projected on the Orion complex was performed with J = 1-0 lines of ¹²CO and ¹³CO with the 13.7 m telescope at the Purple Mountain Observatory. The mean column densities of the Planck gas clumps range from 0.5 to 9.5 × 10²¹ cm^-2, with an average value of (2.9 ± 1.9) × 10²¹ cm^-2. The mean excitation temperatures of these clumps range from 7.4 to 21.1 K, with an average value of 12.1 ± 3.0 K and the average three-dimensional velocity dispersion σ_3D in these molecular clumps is 0.66 ± 0.24 km s^-1. Most of the clumps have σ_NT larger than or comparable to σ_Therm. The H₂ column density of the molecular clumps calculated from molecular lines correlates with the aperture flux at 857 GHz of the dust emission. By analyzing the distributions of the physical parameters, we suggest that turbulent flows can shape the clump structure and dominate their density distribution on large scales, but not function on small scales due to local fluctuations. Eighty-two dense cores are identified in the molecular clumps. The dense cores have an average radius and local thermal equilibrium (LTE) mass of 0.34 ± 0.14 pc and 38⁺⁵ _{- 30} M_⊙, respectively. The structures of low column density cores are more affected by turbulence, while the structures of high column density cores are more affected by other factors, especially by gravity. The correlation of velocity dispersion versus core size is very weak for the dense cores. The dense cores are found to be most likely gravitationally bounded rather than pressure confined. The relationship between M _vir and M _LTE can be well fitted with a power law. The core mass function here is much flatter than the stellar initial mass function. The lognormal behavior of the core mass distribution is most likely determined by internal turbulence.