EPoS Contribution
EPoS Contribution
Isolating signatures of cloud-cloud collisions: a possible trigger of massive star formation

Thomas Haworth
IoA, Cambridge, GB
Feedback from massive stars is effective at dispersing gas and quenching star formation. Therefore in order to produce multiple massive stars, they must all form approximately simultaneously. Simulations have shown that collisions between molecular clouds can provide the quite unusual conditions required to do this. Unfortunately clouds are complex, turbulent objects - as are the systems that result from collisions. This coupled with the fact that we effectively only observe one snapshot in time of any given collision means that they are very hard to identify observationally. It is therefore currently very difficult to verify whether collisions that result in massive star formation are really occuring.
Using synthetic observations based on dynamical models, I and my collaborators are working towards a series of signposts of collision. We have already identified a "broad-bridge" feature in position-velocity diagrams, which we have shown should be long lived and resilient to the effects of feedback once stars form. Such a feature has been observed towards M20, which also has some other evidence of collision. We are now working towards further diagnostics, including distinguishing between collisional and radiative heating using line ratios and intermediate-high J CO transitions. We are also developing methods to more robustly distinguish between distinct, but interacting, clouds and single clouds that have merely undergone some other process such as shear. I will review our findings so far, present new unpublished results and hope to discuss other prospective signposts (e.g. using SiO) at the meeting. Once a collection of signposts is established we can re-evaluate candidate sites of collision to more robustly determine whether cloud-cloud collisions that result in star formation, do indeed happen in reality.
Caption: Left) A snapshot from a simulation of a cloud-cloud collision where a smaller cloud, propagating from the left, collided with a larger. Middle) A simulated CO broad bridge feature resulting from a cloud-cloud collision simulation. Right) A real observed CO broad bridge feature towards M20, a candidate collision site.
Y. Fukui, Nagoya U, JP
E. Tasker, Hokkaido U, JP
K. Torii, Nagoya U, JP
J. Dale, ECU Munich, DE
K. Shima, Hokkaido U, JP
A. Habe, Hokkaido U, JP
K. Takahira, Hokkaido U, JP
Key publication

Suggested Session: Massive Star Formation