Dense Cores and Star-Formation Activities in the Chamaeleon Dark-Cloud Complex

We carried out a C¹⁸O (J = 1−0) survey for dense molecular cores in the Chamaeleon (Cha) I, II, and III dark clouds with the NANTEN millimeter-wave telescope. The present survey covered ∼ 93% of the area where the molecular column density is greater than ∼ 4 × 10²¹ cm^-2, estimated from preceding ¹³CO(J = 1−0) observations. We identified 23 C¹⁸O cores, whose typical mass, radius, peak column density, line width are 22 M⊙, 0.22 pc, 9.7 × 10²¹ cm^-2, and 0.82 km s^-1, respectively. The surface density of classical T Tauri stars abruptly increases for the area whose column density is greater than 10²² cm^-2, suggesting that this value gives a certain threshold value for star formation. The star-formation efficiency varies over a wide range among the three clouds: 13%, 1%, and 0% in Cha I, II, and III, respectively. The C¹⁸O cores in Cha I are characterized by (1) a high column density, (2) being almost in virial equilibrium, and (3) a high Mcore /Mcloud ratio. The cores in Cha III show the opposite trend, and those in Cha II are in between. Such trends suggest that Cha I is a well-evolved or well gravitationally relaxed cloud-core system, which is probably related to the very high star-formation activity in the cloud.