Star Formation Triggered by Snr Impact into Magnetized Neutral Clouds

Present day star formation (SF) takes place in giant molecular clouds (GMCs). These contain a wealth of structures on all length-scales with highly supersonic motions and it is believed that these supersonic motions induce the observed density inhomogeneities in the gas that drive star formation. Suggested candidates for driving supersonic motions and SF include supernova shocks. Considering the physical conditions that are relevant for triggering star formation in interactions involving SN shocks and neutral clouds, we have built diagrams of the SNR radius versus the cloud density in which the conditions above constrain a shaded zone where star formation induced by SN shock front-cloud interactions is allowed. The diagrams are also tested with fully 3-D MHD radiative cooling simulations involving a SNR and a self-gravitating cloud and we find that the numerical analysis is consistent with the results predicted by the diagrams. While the inclusion of a homogeneous magnetic field approximately perpendicular to the impact velocity of the SNR with an intensity ∼ 1 μG within the cloud results only a small shrinking of the star formation zone in the diagrams, a larger magnetic field (∼ 10 μG) causes a significant shrinking, as expected. Applications of our results to real star formation regions in our own galaxy have revealed that their formation could have been triggered by a shock wave produced by a SN explosion under specific values of the initial cloud density and the SNR radius. Finally, we have evaluated the effective global star formation efficiency of this sort of interactions and found that it is smaller than the observed values in our own Galaxy (SFE ∼ 0.01-0.3). This result is consistent with previous work in the literature and also suggests that the mechanism presently investigated, though very powerful to drive structure formation, supersonic turbulence and eventually, local star formation, does not seem to be sufficient to drive global star formation in normal star forming galaxies, nor even when the magnetic field in the neutral clouds is neglected.