2002ApJ...565.1050S

Extensive strip-scan observations of three high-latitude clouds– MBM 32, MBM 54, and MBM 55–were carried out in ¹²CO J=1-0 emission with an angular resolution of 15", or 0.0072 pc (1500 AU) at 100 pc. We resolved clumps with sizes from ∼0.2 pc down to ∼0.02 pc. Most of them have low gas density (≲10² cm^–3) and sizes significantly smaller than their corresponding Jeans lengths. Some of them are well-isolated from the rest of the molecular components, suggesting their (quasi-) stable dynamical state. They provide a clear case for structure formation not caused by gravitational contraction and are most likely formed through thermal instability in interstellar shocks.

We unexpectedly discovered in the position-velocity diagrams a number of localized velocity shifts. Their typical size is 0.05 pc, and some of them exhibit a velocity gradient of ∼40 km.s^–1 pc^–1, which is among the largest ever observed in non-star-forming clouds. None of them have young stellar objects in their vicinity. Contraction of shock-compressed gas may produce rapidly rotating/contracting, but apparently unbound, clumps. These features may provide more evidence for structure formation through thermal instability of shocked gas.