Abundant Cyanopolyynes as a Probe of Infall in the Serpens South Cluster-Forming Region
Abundant Cyanopolyynes as a Probe of Infall in the Serpens South Cluster-Forming Region
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DOI：
10.1093/mnras/stt1671
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发表时间：
2013-09
影响因子：
4.8
通讯作者：
R. Friesen;L. Medeiros;S. Schnee;T. Bourke;J. Francesco;R. Gutermuth;P. Myers
中科院分区：
文献类型：
--
作者：
R. Friesen;L. Medeiros;S. Schnee;T. Bourke;J. Francesco;R. Gutermuth;P. Myers
我们利用Robert C. Byrd Green Bank望远镜的k波段焦平面阵列探测到在蛇蛇南星团形成区多个位置的明亮HC7N J = 21 20发射。HC7N主要朝向尚未形成恒星的冷丝状结构，在很大程度上避开了与小型原恒星群和中央大蛇南星团相关的致密气体。在探测到的地方，HC7N的丰度与附近其他恒星形成区域的丰度相似。对于一些HC7N“团块”，我们发现线质心相对于NH3（1,1）发射的一致变化，以及HC7N非热线宽度的系统增加，我们认为这揭示了在蛇形南内密集细丝的落入运动，其最小质量吸积率为M - 2.5 M⊙Myr−1。NH3与HC7N的相对丰度表明，HC7N正在追踪密度为n - 10 - 4 cm−3的时间尺度为t的气体。由于HC7N的发射峰很少与NH3或连续体的峰同时出现，因此Serpens South的HC7N的丰度可能并不特别显著，但HC7N与NH3同时出现的偶然映射使我们能够在可能没有寻找到HC7N的地区检测到低丰度的HC7N。这一结果将已知的含有大量HC7N辐射的恒星形成区域从典型的静止区域（如金牛座分子云）扩展到更复杂、更活跃的环境。
We have detected bright HC7N J = 21 20 emission toward 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 toward 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 starforming regions. Toward 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 onto dense filaments within Serpens South with minimum mass accretion rates of M � 2 5 M⊙ Myr −1 . The relative abundance of NH3 to HC7N suggests that the HC7N is tracing gas that has been at densities n � 10 4 cm −3 for timescales t . 1 2 × 10 5 yr. 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 HC7N, 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.