<i>SPITZER</i>MAPPING OF MOLECULAR HYDROGEN PURE ROTATIONAL LINES IN NGC 1333: A DETAILED STUDY OF FEEDBACK IN STAR FORMATION

Abstract

We present mid-infrared spectral maps of the NGC 1333 star forming region,\nobtained with the the Infrared Spectrometer on board the Spitzer Space\nTelescope. Eight pure H2 rotational lines, from S (0) to S (7), are detected\nand mapped. The H2 emission appears to be associated with the warm gas shocked\nby the multiple outflows present in the region. A comparison between the\nobserved intensities and the predictions of detailed shock models indicates\nthat the emission arises in both slow (12 - 24 km/s) and fast (36 - 53 km/s)\nC-type shocks with an initial ortho-to-para ratio of ~ 1. The present H2\northo-to-para ratio exhibits a large degree of spatial variations. In the\npost-shocked gas, it is usually about 2, i.e. close to the equilibrium value (~\n3). However, around at least two outflows, we observe a region with a much\nlower (~ 0.5) ortho-to-para ratio. This region probably corresponds to gas\nwhich has been heated-up recently by the passage of a shock front, but whose\northo-to-para has not reached equilibrium yet. This, together with the low\ninitial ortho-to-para ratio needed to reproduce the observed emission, provide\nstrong evidence that H2 is mostly in para form in cold molecular clouds. The H2\nlines are found to contribute to 25 - 50% of the total outflow luminosity, and\nthus can be used to ascertain the importance of star formation feedback on the\nnatal cloud. From these lines, we determine the outflow mass loss rate and,\nindirectly, the stellar infall rate, the outflow momentum and the kinetic\nenergy injected into the cloud over the embedded phase. The latter is found to\nexceed the binding energy of individual cores, suggesting that outflows could\nbe the main mechanism for core disruption.\n