Dense cores in dark clouds.: XIV.: N2H+ (1-0) maps of dense cloud cores
Dense cores in dark clouds.: XIV.: N2H+ (1-0) maps of dense cloud cores
复制标题
DOI：
10.1086/340195
复制
发表时间：
2002-06-10
影响因子：
4.9
通讯作者：
Tafalla, M
中科院分区：
文献类型：
--
作者：
Caselli, P;Benson, PJ;Tafalla, M
我们目前的N2 H+（1-0）在大约60个低质量云核已经映射在NH3（1，1）反转过渡线广泛的映射调查的结果。该调查是在FCRAO天线上进行的，角分辨率为54”，比以前在Haystack望远镜上进行的氨观测精细约1.5倍。N2 H+和NH3图之间的比较显示了两种分子物种在大小和形态上的强烈相似性，这表明它们正在追踪相同的物质，特别是在无星核中。有恒星的核心通常有N2 H+比NH3小2倍的地图大小，表明与无恒星的核心相比，存在更密集和更集中的气体。平均长宽比近似于2。NH3和N2 H+柱密度和激发温度之间的显着相关性被发现在无星的核心，但不是在有星的核心，这表明不同的化学演化的两个物种。无星核的质量（M vir hi 3 M）比有星核的质量（M vir hi 9 M）小。速度梯度在0.5 ~ 6 km s（-1）pc（-1）之间，与NH3数据所发现的相似，旋转动能与引力能的比值β在10（-4）~ 0.07之间，表明旋转在支撑地核的能量上并不占主导地位。局部速度梯度在大小和方向上都有显著变化，表明存在复杂的运动，不能解释为简单的固体旋转。无星核的积分强度剖面呈现中心扁平，符合球对称密度定律n与r（-α）成正比，其中当r < r（break）时α = 1.2，当r > r（break）时α = 2，r（break）近似于0.03 pc。与观测到的亚毫米波连续辐射一致，用α大于或等于2的单密度幂律来模拟有恒星的核是更好的。线的宽度在整个核心变化，但我们没有发现一个总的趋势：有显着的积极和消极的线性相关性之间的D v和影响参数B的核心。线宽的偏差与平均线宽相关，表明视线包含10个相干长度。相应的相干长度值约为0.01pc，与MHD波的预期截止波长相近。这种相似性可以解释在小尺度上线宽的增加的一致性。尽管有更好的角分辨率，但大多数N2 H+和NH3图显示出类似的简单结构，具有单峰且没有伸长。
We present results of an extensive mapping survey of N2H+ (1-0) in about 60 low-mass cloud cores already mapped in the NH3 ( 1, 1) inversion transition line. The survey has been carried out at the FCRAO antenna with an angular resolution of 54", about 1.5 times finer than the previous ammonia observations made at the Haystack telescope. The comparison between N2H+ and NH3 maps shows strong similarities in the size and morphology of the two molecular species, indicating that they are tracing the same material, especially in starless cores. Cores with stars typically have map sizes about a factor of 2 smaller for N2H+ than for NH3, indicating the presence of denser and more centrally concentrated gas compared to starless cores. The mean aspect ratio is similar to2. Significant correlations are found between NH3 and N2H+ column densities and excitation temperatures in starless cores, but not in cores with stars, suggesting a different chemical evolution of the two species. Starless cores are less massive ( M vir hi 3 M) than cores with stars ( M vir hi 9 M). Velocity gradients range between 0.5 and 6 km s(-1) pc(-1), similar to what has been found with NH3 data, and the ratio beta of rotational kinetic energy to gravitational energy has magnitudes between similar to10(-4) and 0.07, indicating that rotation is not energetically dominant in the support of the cores. Local velocity gradients show significant variation in both magnitude and direction, suggesting the presence of complex motions not interpretable as simple solid-body rotation. Integrated intensity profiles of starless cores present a central flattening and are consistent with a spherically symmetric density law n proportional to r(-alpha), where alpha = 1.2 for r < r(break) and alpha = 2 for r > r(break), with r(break) similar to0.03 pc. Cores with stars are better modeled with single density power laws with alpha greater than or equal to2, in agreement with observations of submillimeter continuum emission. Line widths change across the core, but we did not find a general trend: there are cores with significant positive as well as negative linear correlations between D v and the impact parameter b. The deviation in line width correlates with the mean line width, suggesting that the line of sight contains 10 coherence lengths. The corresponding value of the coherence length, similar to0.01 pc, is similar to the expected cutoff wavelength for MHD waves. This similarity may account for the increased coherence of line widths on small scales. Despite finer angular resolution, the majority of N2H+ and NH3 maps show a similar simple structure, with single peaks and no elongation.