No abstract

Using the PMO-13.7m millimeter telescope at Delingha in China, we have conducted a large-scale simultaneous survey of 12 CO, 13 CO, and C 18 O J=1-0 emission toward the Rosette molecular cloud (RMC) region with a sky coverage of 3.5 • × 2.5 • . The majority of the emission in the region comes from the RMC complex with velocities lying in the range from -2 km s −1 to 20.5 km s −1 . Beyond this velocity range, 73 molecular clumps are identified with kinematic distances from 2.4 kpc to 11 kpc. Based on the spatial and velocity distribution, nine individual clouds, C1-C9, have been identified for the RMC complex. It appears that the C3 cloud is different from other clouds in the RMC complex in view of its characteristic velocity, excitation temperature, and velocity dispersion. Most of the young stellar clusters in the region are located in positions of both high column density and high excitation temperature. Seven new molecular filaments are discovered in the RMC complex. Evidence for cloud-cloud collision is found in the region of young stellar clusters REFL9 and PouF, showing that these young stellar clusters probably result from a cloud-cloud collision. The abundance ratios of 13 CO to C 18 O in the region have a mean value of 13.7 which is 2.5 times larger than the solar system value, showing that UV photons from the nearby OB clusters have strong influence on the chemistry of clouds in the RMC complex.

We have conducted a large-field simultaneous survey of 12 CO, 13 CO, and C 18 O J = 1 − 0 emission toward the Orion A giant molecular cloud (GMC) with a sky coverage of ∼ 4.4 deg 2 using the PMO-13.7 m millimeter-wavelength telescope. We use the probability distribution function of the column density (N-PDF) to investigate the distribution of molecular hydrogen in the Orion A GMC. The H 2 column density, derived from the 13 CO emission, of the GMC is dominated by log-normal distribution in the range from ∼4×10 21 to ∼1.5×10 23 cm −2 with excesses both at the low-density and high-density ends. The excess of the low-density end is possibly caused by an extended and low-temperature (∼10 K) component with velocities in the range of 5−8 km s −1 . Compared with the northern sub-regions, the southern sub-regions of the Orion A GMC contain less gas with column density in N H2 > 1.25 × 10 22 cm −2 . The dispersions of the N-PDFs of the sub-regions are found to correlate with the evolutionary stages of the clouds across the Orion A GMC. The structure hierarchy of Orion A GMC is explored with the DENDROGRAM algorithm, and it is found that the GMC is composed of two branches. All structures except one in the tree have virial parameters less than 2, indicating self-gravity is important on the spatial scales from ∼0.3 to ∼4 pc. Although power-laws and departures from log-normal distributions are found at the high-density end of N-PDFs of active star-forming regions, the N-PDFs of structures in the Orion A GMC are predominantly log-normal on scales from R∼0.4 to 4 pc.