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R. Shah (University of Illinois at Urbana-Champaign), J. McMullin, A. Wootten (NRAO)
We present a high resolution (~10\arcsec) study to identify cold gas condensations in the northwest region of the Serpens Molecular Cloud with observations from the Berkeley--Illinois--Maryland Association (BIMA) array of the deuterated molecule {\rm DCO+}. Cold gas clumps are particularly interesting in light of recent results on the dark cloud L1544 and the clustered star forming regions NGC1333 IRAS4 and L1251A. These studies suggest that ambipolar diffusion models are insufficient to explain the large size scales of observed CS and {\rm HCO+} collapse line profiles. Deuterated molecules and molecular fractionation ratios, in particular {\rm DCO+/HCO+}, trace cold, dense, quiescent gas associated with the evolution of pre-protostellar cores. In such regions, previous single--aperture studies of the {\rm DCO+/HCO+} column density ratio indicate that it is elevated to values between 0.1-10%. Chemical models have been used by these same studies to estimate upper limits on the electron fraction in molecular clouds: Xe^-=ne^-/n\rm H_2, typically observed to be 10-8 . These values of Xe^- are consistent with theoretical requirements of ambipolar diffusion models of protostellar evolution. Studies of the {\rm DCO+/HCO+} distribution in more complex, clustered, star forming regions requires high resolution imaging to separate regions influenced by energetic processes (e.g. outflows) from any cold gas condensations. We present full-synthesis maps of the {\rm DCO+}~J=1arrow 0 transition and a deuterium fractionation study towards S68~FIRS1. Our observations identify a number of features without dust continuum counterparts alongside known Class 0 protostars. We will discuss correlations with several other tracers of mass and energy content.
Funding for this work is through NRAO and BIMA. The National Radio Astronomy Observatory is operated by Associated Universities Inc., under cooperative agreement with the National Science Foundation. The BIMA Array is operated under contract with the National Science Foundation.