2012ApJ...756...76W

A survey toward 674 Planck cold clumps of the Early Cold Core Catalogue (ECC) in the J = 1-0 transitions of ¹²CO, ¹³CO, and C¹⁸O has been carried out using the Purple Mountain Observatory 13.7 m telescope. Six hundred seventy-three clumps were detected with ¹²CO and ¹³CO emission, and 68% of the sample has C¹⁸O emission. Additional velocity components were also identified. A close consistency of the three line peak velocities was revealed for the first time. Kinematic distances are given for all the velocity components, and half of the clumps are located within 0.5 and 1.5 kpc. Excitation temperatures range from 4 to 27 K, slightly larger than those of T_d. Line width analysis shows that the majority of ECC clumps are low-mass clumps. Column densities N_H2 span from 10²⁰ to 4.5x10²²/cm2 with an average value of (4.4 ±3.6)x10²¹/cm2. N_H2 cumulative fraction distribution deviates from the lognormal distribution, which is attributed to optical depth. The average abundance ratio of the ¹³CO to C¹⁸O in these clumps is 7.0±3.8, higher than the terrestrial value. Dust and gas are well coupled in 95% of the clumps. Blue profile asymmetry, red profile asymmetry, and total line asymmetry were found in less than 10% of the clumps, generally indicating that star formation is not yet developed. Ten clumps were mapped. Twelve velocity components and 22 cores were obtained. Their morphologies include extended diffuse, dense, isolated, cometary, and filament, of which the last is the majority. Twenty cores are starless, and only seven cores seem to be in a gravitationally bound state. Planck cold clumps are the most quiescent among the samples of weak red IRAS, infrared dark clouds, UC H II candidates, extended green objects, and methanol maser sources, suggesting that Planck cold clumps have expanded the horizon of cold astronomy.