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We present mid-infrared spectral maps of the NGC 1333 star forming region,obtained with the the Infrared Spectrometer on board the Spitzer SpaceTelescope. Eight pure H2 rotational lines, from S (0) to S (7), are detectedand mapped. The H2 emission appears to be associated with the warm gas shockedby the multiple outflows present in the region. A comparison between theobserved intensities and the predictions of detailed shock models indicatesthat 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 of ~ 1. The present H2ortho-to-para ratio exhibits a large degree of spatial variations. In thepost-shocked 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 muchlower (~ 0.5) ortho-to-para ratio. This region probably corresponds to gaswhich has been heated-up recently by the passage of a shock front, but whoseortho-to-para has not reached equilibrium yet. This, together with the lowinitial ortho-to-para ratio needed to reproduce the observed emission, providestrong evidence that H2 is mostly in para form in cold molecular clouds. The H2lines are found to contribute to 25 - 50% of the total outflow luminosity, andthus can be used to ascertain the importance of star formation feedback on thenatal cloud. From these lines, we determine the outflow mass loss rate and,indirectly, the stellar infall rate, the outflow momentum and the kineticenergy injected into the cloud over the embedded phase. The latter is found toexceed the binding energy of individual cores, suggesting that outflows couldbe the main mechanism for core disruption.

Spitzer mapping of molecular hydrogen pure rotational lines in NGC 1333: A detailed study of feedback in star formation