Massive star formation in the Carina nebula complex and Gum 31. I. the Carina nebula complex

Herein, we present results from observations of the ¹²CO (J = 1-0), ¹³CO (J = 1-0), and ¹²CO (J = 2-1) emission lines toward the Carina nebula complex (CNC) obtained with the Mopra and NANTEN2 telescopes. We focused on massive-star-forming regions associated with the CNC including the three star clusters Tr 14, Tr 15, and Tr 16, and the isolated WR-star HD 92740. We found that the molecular clouds in the CNC are separated into mainly four clouds at velocities -27, -20, -14, and -8 km s^-1. Their masses are 0.7 × 10⁴ M_⊙, 5.0 × 10⁴ M_⊙, 1.6 × 10⁴ M_⊙, and 0.7 × 10⁴ M_⊙, respectively. Most are likely associated with the star clusters, because of their high ¹²CO (J = 2-1)/¹²CO (J = 1-0) intensity ratios and their correspondence to the Spitzer 8 μm distributions. In addition, these clouds show the observational signatures of cloud-cloud collisions. In particular, there is a V-shaped structure in the position-velocity diagram and a complementary spatial distribution between the -20 km s^-1 cloud and the -14 km s^-1 cloud. Furthermore, we found that SiO emission, which is a tracer of a shocked molecular gas, is enhanced between the colliding clouds by using ALMA archive data. Based on these observational signatures, we propose a scenario wherein the formation of massive stars in the clusters was triggered by a collision between the two clouds. By using the path length of the collision and the assumed velocity separation, we estimate the timescale of the collision to be ∼1 Myr. This is comparable to the ages of the clusters estimated in previous studies.