THE INITIAL CONDITIONS OF CLUSTERED STAR FORMATION. II. N2H+ OBSERVATIONS OF THE OPHIUCHUS B CORE
THE INITIAL CONDITIONS OF CLUSTERED STAR FORMATION. II. N2H+ OBSERVATIONS OF THE OPHIUCHUS B CORE
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DOI：
10.1088/0004-637x/708/2/1002
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发表时间：
2009-11
期刊：
影响因子：
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通讯作者：
R. Friesen;R. Friesen;R. Friesen;J. D. Francesco;J. D. Francesco;Y. Shimajiri;S. Takakuwa
中科院分区：
文献类型：
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作者：
R. Friesen;R. Friesen;R. Friesen;J. D. Francesco;J. D. Francesco;Y. Shimajiri;S. Takakuwa
我们给出了一张Nobeama 45米射电望远镜地图和澳大利亚望远镜紧凑型阵列，将N2H+1-0发射的观测指向蛇夫座分子云中聚集的、低质量恒星形成的Oph B核心。我们将这些数据与OphB的高分辨率NH3(1，1)和(2，2)观测结果进行了比较。我们使用3D Clumpfind识别单盘N2H+图中的发射特征，发现N2H+“团”与以前在NH3(1，1)发射中识别的相似特征很好地匹配，但经常与850μm连续谱中以类似分辨率识别的团块相抵消。OphB2亚核的宽线宽表明，非热运动占核心运动学的主导地位，并在密度为n∼3×10 5 cm−3时保持跨音速，散射较大，与N(H2)没有趋势。相比之下，OphB1和B3的非热运动是亚音速的，变化很小，但也没有随H2柱密度变化的趋势。在所有的Oph B中，非热N2H+的线宽比NH3所跟踪的线宽要窄得多，这使得NH3和N2H+不太可能跟踪相同的物质，但两个物种的vLSR都很一致。我们发现了来自周围环境气体的OphB1吸积的证据。NH3/N2H+丰度比对于无恒星的OphB1比对于原恒星的OphB2更大，类似于最近在其他恒星形成区域的观测结果。干涉仪观测揭示了N2H+1-0发射中的小尺度结构，这再次与连续谱发射相抵消。没有发现干涉N2H+发射峰与连续谱团重合。特别是，∼1M☉B2-MM8团块与N2H+发射极小值有关，并被一个破碎的环状N2H+发射结构所包围，暗示着N2H+的耗尽。我们发现了一个很强的总体趋势，即随着OphB中N(H2)的增加，N2H+丰度降低，这与对NH3的发现相一致。
We present a Nobeyama 45 m Radio Telescope map and Australia Telescope Compact Array pointed observations of N2H+ 1-0 emission toward the clustered, low-mass star-forming Oph B Core within the Ophiuchus molecular cloud. We compare these data with previously published results of high-resolution NH3 (1,1) and (2,2) observations in Oph B. We use 3D clumpfind to identify emission features in the single-dish N2H+ map, and find that the N2H+ “clumps” match well similar features previously identified in NH3 (1,1) emission, but are frequently offset to clumps identified at similar resolution in 850 μm continuum emission. Wide line widths in the Oph B2 sub-Core indicate that non-thermal motions dominate the Core kinematics, and remain transonic at densities n ∼ 3 × 105 cm−3 with large scatter and no trend with N(H2). In contrast, non-thermal motions in Oph B1 and B3 are subsonic with little variation, but also show no trend with H2 column density. Over all of Oph B, non-thermal N2H+ line widths are substantially narrower than those traced by NH3, making it unlikely NH3 and N2H+ trace the same material, but the vLSR of both species agree well. We find evidence for accretion in Oph B1 from the surrounding ambient gas. The NH3/N2H+ abundance ratio is larger toward starless Oph B1 than toward protostellar Oph B2, similar to recent observational results in other star-forming regions. The interferometer observations reveal small-scale structure in N2H+ 1-0 emission, which are again offset from continuum emission. No interferometric N2H+ emission peaks were found to be coincident with continuum clumps. In particular, the ∼1 M☉ B2-MM8 clump is associated with an N2H+ emission minimum and surrounded by a broken ring-like N2H+ emission structure, suggestive of N2H+ depletion. We find a strong general trend of decreasing N2H+ abundance with increasing N(H2) in Oph B which matches that found for NH3.