NANTEN Observations of the Pipe Nebula; A Filamentary Massive Dark Cloud with Very Low Star-Formation Activity

We present molecular line observations toward the “Pipe Nebula” in the J = 1−0 lines of 12CO, 13CO, and C18O by using “NANTEN” telescope. An area of ∼ 27 deg2 was covered at a 4′ grid spacing with a 2′.7 beam in 12CO. The 12CO velocity-integrated intensity map and channel maps show a filamentary distribution. The total mass of the 12CO- and 13CO-emitting gas is estimated to be ∼ 10000 M⊙ and ∼ 3000 M⊙ , respectively. We have identified 14 C18O cores whose mass is typically ∼ 30 M⊙ . Star formation is active only in the B 59 region. This activity is best demonstrated by a newly detected CO outflow toward the center of B 59. We suggest that the dynamical effects of tau Sco may be responsible for triggering star formation only in the B 59 region. The C18O column density toward B 59 is extremely high compared with the rest of the cloud. This confirms that high C18O column density is a necessary condition of star formation as previously suggested. Although the star-formation efficiency is estimated to be quite low, ≲ 0.1%, except for B 59, the existence of the C18O cores suggests that there is molecular gas that is massive and dense enough to form stars, and that star formation is likely to occur in the near future.