2009ApJ...698.1244M

We present mid-infrared spectral maps of the NGC 1333 star-forming region, obtained with the infrared spectrometer on board the Spitzer Space Telescope. Eight pure H₂ rotational lines, from S(0) to S(7), are detected and mapped. The H₂ emission appears to be associated with the warm gas shocked by the multiple outflows present in the region. A comparison between the observed intensities and the predictions of detailed shock models indicates that the emission arises in both slow (12-24 km/s) and fast (36-53 km/s) C-type shocks with an initial ortho-to-para ratio (opr) ≲1. The present H₂ opr exhibits a large degree of spatial variations. In the postshocked gas, it is usually about 2, i.e., close to the equilibrium value (∼3). However, around at least two outflows, we observe a region with a much lower (∼0.5) opr. This region probably corresponds to gas which has been heated up recently by the passage of a shock front, but whose ortho-to-para has not reached equilibrium yet. This, together with the low initial opr needed to reproduce the observed emission, provide strong evidence that H₂ is mostly in para form in cold molecular clouds. The H₂ lines are found to contribute to 25%-50% of the total outflow luminosity, and thus can be used to ascertain the importance of star formation feedback on the natal cloud. From these lines, we determine the outflow mass loss rate and, indirectly, the stellar infall rate, the outflow momentum and the kinetic energy injected into the cloud over the embedded phase. The latter is found to exceed the binding energy of individual cores, suggesting that outflows could be the main mechanism for core disruption.