33.8 GHz CCS survey of molecular cores in dark clouds

We have conducted a survey of the CCS J_N = 3₂-2₁ line toward 11 dark clouds and star-forming regions at 30″ spatial resolution and 0.054 km s^-1 velocity resolution. CCS was detected only in quiescent clouds, not in active star-forming regions. The CCS distribution shows remarkable clumpy structure, and 25 clumps are identified in seven clouds. Seven clumps with extremely narrow nonthermal line widths (<0.1 km s^-1) are among the most quiescent clumps ever found. The CCS clumps tend to exist around the higher density regions traced by NH₃ emission or submillimeter continuum sources, and the distribution is not spherically symmetric. Variation of the CCS abundance was suggested as an indicator of the evolutionary status of star formation. However, we can only find a weak correlation between N(CCS) and n_H2,vir. The velocity distributions of CCS clouds reveal that a systematic velocity pattern generally exists. The most striking feature in our data is a ring structure in the position-velocity diagram of L1544 with an well-resolved inner hole of 0.04 pc x 0.13 km s_-1 and an outer boundary of 0.16 pc x 0.55 km s_-1. This position-velocity structure clearly indicates an edge-on disk or ring geometry, and it can be interpreted as a collapsing disk with an infall velocity ≳0.1 km s_-1 and a rotational velocity less than our velocity resolution. Nonthermal line width distribution is generally coherent in CCS clouds, which could be evidence for the termination of Larson's Law at small scales, ∼0.1 pc.