A statistical study of giant molecular clouds traced by13CO, C18O, CS, and CH3OH in the disk of NGC1068 based on ALMA observations
A statistical study of giant molecular clouds traced by13CO, C18O, CS, and CH3OH in the disk of NGC1068 based on ALMA observations
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基于ALMA观测的NGC1068盘面13CO、C18O、CS、CH3OH巨分子云统计研究
DOI：
10.1093/pasj/psw122
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
Tamura Yoichi
中科院分区：
文献类型：
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作者：
Tosaki Tomoka;Kohno Kotaro;Harada Nanase;Tanaka Kunihiko;Egusa Fumi;Izumi Takuma;Takano Shuro;Nakajima Taku;Taniguchi Akio;Tamura Yoichi
本文报道了14个（98 pc）分辨率的阿尔马（ALMA）观测结果，它们分别是~（13）CO（J= 1 - 0），~（18）C O（J= 1-0），~（18）CS（J= 2-1），和ch 3oh（JK= 2K-1 K）分子转动谱线（4.2 kpc）区域的巨大分子云（GMC）的物理和化学性质，并测试这些GMC-尺度特性与更大尺度的银河系环境有关。使用推导出的13 CO立方体，我们采用CLUMPFIND算法识别了187个高显著性（>8 σ）GMC。根据~（13）CO数据计算出的GMC的分子气体质量范围为1.8 × 10 ~ 4 ~ 4.2 × 107 M ~（13）。本文首次获得了NGC 1068中巨磁物质的质量函数，其分辨率为1000 pc。我们发现质量函数的斜率γ = −1.25 ± 0.07，质量范围为M。这比银河系、M 51和NGC 300的盘区域的GMC要浅。此外，我们还发现，在M51的核棒区，GMC质量函数的高质量截止出现在M51处，这比M51的核棒区大一个数量级，表明更大质量的云在NGC 1068的质量收支中占主导地位。观测到的C18 O（J= 1-0）/13 CO（J= 1-0）强度比在已识别的GMC中相当均匀（0.27 ± 0.05）。相比之下，CH_3OH（JK= 2K-1 K）/~（13）CO（J= 1-0）的比值在整个盘上表现出显著的空间变化，在棒端附近的值最小（<0.03），而沿沿着螺旋臂的比值较大（<0.1-0.2）。我们发现，GMCs与可检测到的甲醇排放往往有系统的更大的速度宽度比那些没有甲醇排放，这表明（相对较弱）的冲击是负责的增强的CH 3OH/13 CO比率的GMCs在NGC 1068的磁盘。
We present 14 (98 pc) resolution ALMA observations of13CO(J= 1–0), C18O(J= 1–0), CS(J= 2–1), and CH3OH(JK= 2K–1K) molecular rotational lines in the central 1΄ (4.2 kpc) diameter region of NGC 1068 to study the physical and chemical properties of giant molecular clouds (GMCs) and to test whether these GMC-scale properties are linked to the larger-scale galactic environment. Using the derived13CO cube, we have identified 187 high-significance (>8 σ) GMCs by employing theCLUMPFINDalgorithm. The molecular gas masses of GMCs (), derived from the13CO data, range from 1.8 × 104M⊙to 4.2 × 107M⊙. A mass function of GMCs in NGC 1068 has been obtained for the first time at ∼100 pc resolution. We find the slope of the mass function γ = −1.25 ± 0.07 for a mass range ofM⊙. This is shallower than the GMCs in the disk regions of the Milky Way, M 51, and NGC 300. Further, we find that the high mass cut-off of the GMC mass function occurs atM⊙, which is an order of magnitude larger than that in the nuclear bar region of M 51, indicating that the more massive clouds dominate the mass budget in NGC 1068. The observed C18O(J= 1–0)/13CO(J= 1–0) intensity ratios are found to be fairly uniform (0.27 ± 0.05) among the identified GMCs. In contrast, the CH3OH(JK= 2K–1K)/13CO(J= 1–0) ratios exhibit striking spatial variation across the disk, with the smallest values around the bar-end (<0.03), and larger ratios along the spiral arms (∼0.1–0.2). We find that GMCs with detectable methanol emission tend to have systematically larger velocity widths than those without methanol emission, suggesting that (relatively weak) shocks are responsible for the enhancement of the CH3OH/13CO ratios of GMCs in the disk of NGC 1068.