| Abstract | We have detected bright HC₇N J=21-20 emission towards multiple locations in the Serpens South cluster-forming region using the K-Band Focal Plane Array at the Robert C. Byrd Green Bank Telescope. HC7N is seen primarily towards cold filamentary structures that have yet to form stars, largely avoiding the dense gas associated with small protostellar groups and the main central cluster of Serpens South. Where detected, the HC₇N abundances are similar to those found in other nearby star-forming regions. Towards some HC₇N 'clumps', we find consistent variations in the line centroids relative to NH₃(1,1) emission, as well as systematic increases in the HC₇N non-thermal line widths, which we argue reveal infall motions on to dense filaments within Serpens South with minimum mass accretion rates of M ~2-5M⊙ Myr⁻¹. The relative abundance of NH₃ to HC₇N suggests that the HC₇N is tracing gas that has been at densities n ~10₇ cm⁻³ for time-scales t ≲ 1-2 × 10⁵yr. Since HC₇N emission peaks are rarely co-located with those of either NH₃ or continuum, it is likely that Serpens South is not particularly remarkable in its abundance of HC₇ N, but instead the serendipitous mapping of HC₇N simultaneously with NH₃ has allowed us to detect HC₇N at low abundances in regions where it otherwise may not have been looked for. This result extends the known star-forming regions containing significant HC₇N emission from typically quiescent regions, like the Taurus molecular cloud, to more complex, active environments. |
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