DEPENDENCE OF THE TURBULENT VELOCITY FIELD ON GAS DENSITY IN L1551
DEPENDENCE OF THE TURBULENT VELOCITY FIELD ON GAS DENSITY IN L1551
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DOI：
10.1088/0004-637x/718/2/1019
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发表时间：
2010-08
期刊：
影响因子：
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通讯作者：
A. Yoshida;Y. Kitamura;Y. Shimajiri;R. Kawabe
中科院分区：
文献类型：
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作者：
A. Yoshida;Y. Kitamura;Y. Shimajiri;R. Kawabe
利用Nobeyama 45 m射电望远镜在12CO（1-0）线上以22″的高效分辨率（160 pc的有效分辨率为0.017 pc）对大小约为2pc × 2pc的L1551整个分子云进行了映射观测，并将12CO数据与Nobeyama射电天文台数据库中的13CO（1-0）和C18O（1-0）数据进行了分析。在校正了光深和视距积分的影响后，推导出了新的非热谱线宽度-尺寸关系σNT∝L γ。为了研究固有湍流的特性，排除了射流的影响。12CO、13CO和C18O谱线的关系分别为(σNT/km s−1)=(0.18±0.010)(L/pc)0.45±0.095、（0.20±0.020）（L/pc）0.48±0.091和（0.22±0.050）（L/pc）0.54±0.21，表明湍流的谱线宽度-尺寸关系对我们观测到的分子谱线的依赖非常弱，即在102 ~ 103和103 ~ 104 cm−3的密度范围内，谱线宽度-尺寸关系没有变化。此外，关系式表明L1551在小于0.6 pc的尺度上不可压缩湍流占主导地位。然而，由关系式转换而来的功率谱指数似乎比不可压缩流的柯尔莫哥洛夫谱的功率谱指数要大。这种差异可以用L1551湍流速度场的各向异性来解释，正如MHD湍流所期望的那样。实际上，质心速度波动的自相关函数在整个金牛座云的磁场方向上显示出较大的相关性，这与不可压缩MHD流的数值模拟结果一致。
We have carried out mapping observations of the entire L1551 molecular cloud with about 2 pc × 2 pc size in the 12CO(1–0) line with the Nobeyama 45 m radio telescope at the high effective resolution of 22″ (corresponding to 0.017 pc at the distance of 160 pc), and analyzed the 12CO data together with the 13CO(1–0) and C18O(1–0) data from the Nobeyama Radio Observatory database. We derived the new non-thermal line width–size relations, σNT ∝ L γ, for the three molecular lines, corrected for the effect of optical depth and the line-of-sight integration. To investigate the characteristic of the intrinsic turbulence, the effects of the outflows were removed. The derived relations are (σNT/km s−1) = (0.18 ± 0.010)(L/pc)0.45 ± 0.095, (0.20 ± 0.020)(L/pc)0.48 ± 0.091, and (0.22 ± 0.050) (L/pc)0.54 ± 0.21 for the 12CO, 13CO, and C18O lines, respectively, suggesting that the line width–size relation of the turbulence very weakly depends on our observed molecular lines, i.e., the relation does not change between the density ranges of 102–103 and 103–104 cm−3. In addition, the relations indicate that incompressible turbulence is dominant at the scales smaller than 0.6 pc in L1551. The power spectrum indices converted from the relations, however, seem to be larger than that of the Kolmogorov spectrum for incompressible flow. The disagreement could be explained by the anisotropy in the turbulent velocity field in L1551, as expected in MHD turbulence. Actually, the autocorrelation functions of the centroid velocity fluctuations show larger correlation along the direction of the magnetic field measured for the whole Taurus cloud, which is consistent with the results of numerical simulations for incompressible MHD flow.