Molecular Clouds Toward RCW49 and Westerlund 2: Evidence for Cluster Formation Triggered by Cloud-Cloud Collision
Abstract
We have made CO(J = 2-1) observations toward the H II region RCW 49 and its ionizing source, the rich stellar cluster Westerlund 2, with the NANTEN2 submillimeter telescope. These observations have revealed that two molecular clouds in velocity ranges of -11 to +9 km s-1 and 11 to 21 km s-1, respectively, show remarkably good spatial correlations with the Spitzer IRAC mid-infrared image of RCW 49, as well a velocity structures indicative of localized expansion around the bright central regions and stellar cluster. This strongly suggests that the two clouds are physically associated with RCW 49. We obtain a new kinematic distance estimate to RCW 49 and Wd2 of 5.4+1.1 -1.4 kpc, based on the mean velocity and velocity spread of the associated gas. We argue that the acceleration of the gas by stellar winds from Westerlund 2 is insufficient to explain the entire observed velocity dispersion of the molecular gas, and suggest a scenario in which a collision between the two clouds ~4 Myr ago may have triggered the formation of the stellar cluster.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2009
- DOI:
- 10.1088/0004-637X/696/2/L115
- arXiv:
- arXiv:0904.0286
- Bibcode:
- 2009ApJ...696L.115F
- Keywords:
-
- H II regions;
- ISM: clouds;
- ISM: individual: RCW 49;
- open clusters and associations: individual: Westerlund 2;
- Astrophysics - Galaxy Astrophysics
- E-Print:
- A version with higher resolution figures is available from http://www.a.phys.nagoya-u.ac.jp/~naoko/research/apjl2009/fur09_rev_highreso.pdf