KMS of Xinjiang Astronomical Observatory, CAS
| 具有下落运动的大质量分子云团块的搜寻与统计研究 | |
| Alternative Title | Searching and Studying Infall Motionsin Massive Star-Forming Regions |
何玉新
| |
| Subtype | 博士 |
| Thesis Advisor | 加尔肯·叶生别克 ; 周建军 |
| 2016 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 天体物理 |
| Keyword | 恒星形成 运动学与动力学 星际分子 |
| Abstract | 具有下落运动的大质量恒星形成区是研究大质量恒星形成动力学过程很好的样本。通过对这些区域的研究，可以为大质量恒星形成的动力学过程提出更准确的限制，促进对大质量恒星形成的理解。但是至今这样的样本仍然很少。因此我们在大质量分子云团块中搜寻下落运动，以获得一个大样本的下落候选体，并进一步对这些源的物理性质进行统计研究。 首先，我们从ATLASGAL巡天和MALT90第一、 二年巡天重叠区域中选取405个致密团块作为研究样本。而且样本源落在Spitzer GLIMPSE/MIPSGAL中红外巡天范围。我们使用中红外分类方法把样本源分为三类：无星核、原恒星核和超致密电离氢区。通过研究样本源质量和线尺度的关系，得出0.05gcm-2是大质量恒星形成团块尺度面密度下限。然后我们使用光学厚分子谱线HCO+(1-0)、HNC(1-0) 和光学薄分子谱线N2H+(1-0)在样本源中搜寻下落运动。 通过分析光学厚分子HCO+(1-0)、 HNC(1-0)谱线的不对称性和HCO+(1-0)分子谱线轮廓在成图区域的分布，最终确定了131个比较可靠的下落运动候选体。HCO+(1-0)分子谱线相对于HNC(1-0)更易表现出蓝不对称性，表明HCO+(1-0)更适合示踪团块的下落运动。下落运动在无星核、原恒星核和超致密电离氢区阶段的探测率分别为0.345、0.3861和0.2152。在超致密电离氢区阶段，团块下落运动的探测率依旧很高，表明团块仍然在有效的聚集物质。统计结果表明团块的870微米连续辐射的峰值流量和质量随演化增加，而团块的质量下落速率随演化减小。 然后，我们从所有剩余的MALT90巡天数据中选取327个新的样本源，并使用上述方法确定了100 个新的下落候选体。现在共有732个团块，其中的231个为下落候选体，501 个为没有探测到下落运动的团块。我们沿用文献[67]中对MALT90巡天数据的分类，把样本源分为无星核、 原恒星核、 电离氢区和光子离解区阶段。相应的每个阶段下落候选体探测率分别为41.2%、36.6%、30.6% 和12.7%。统计结果表明下落候选体相对没有下落运动的团块具有更高的柱密度和体密度。对于下落候选体，质量下落速率在无星核、原恒星核、电离氢区和光子离解区阶段分布的中位数分别为2.6×10−3、7.0×10−3、6.5×10-3和5.5×10−3 M⊙ yr−1。这些值表明下落候选体在比较晚的演化阶段仍然很有效的聚集物质。另外下落候选体和无下落运动团块的质量都表现为从无星核阶段到原恒星核阶段，然后到电离氢区阶段增加。通过拟合得到下落候选体和无下 落运动团块的质量函数，指数分别为2.04±0.16和2.17±0.31。指数与恒星的初始质量函数的指数（2.35）和Planck冷核的初始质量函数的指数（2.0）接近。 |
| Other Abstract | Massive star-forming regions with observed infall motions are good sites for s-tudying the birth of massive stars. However, there are still few high-mass infall candi-dates. Further observations are needed to constrain better the physical properties of the infall, including its spatial distribution, mass infall rate and chemical effect, and to un-derstand its relation with respect to other dynamical processes, including outflow, disc accretion and core fragmentation. HCO+(1-0), HNC(1-0) and N2H+(1-0) lines were used to search infall candidates in massive star-forming regions. We then performed statistical analysis on properties of infall candidates. First, in this paper, we extracted 405 compact sources from the APEX Tele-scope Large Area Survey of the Galaxy (ATLASGAL) compact sources that also have been observed in the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey during Years 1 and 2.These observations are complemented with Spitzer GLIMPSE/MIPSGAL mid-IR survey data to help classify the elected star-forming clumps into three evolutionary stages: pre-stellar, proto-stellar and UCHII regions. The results suggest that 0.05 g cm−2 is a reliable empirical lower bound for the clump surface densities required for massive-star formation to occur. The optically thick HCO+(1-0) and HNC(1-0) lines, as well as the optically thin N2H+(1-0) line were used to search for infall motions toward these sources. By analyzing the asymmetries of the optically thick HCO+(1-0) and HNC(1-0) lines and the mapping observation-s of HCO+(1-0), a total of 131 reliable infall candidates have been identified. The HCO+(1-0) line shows the highest occurrence of obvious asymmetric features, suggesting that it may be a better infall motion tracer than other lines such as HNC(1-0).The detection rates of infall candidates toward pre-stellar, proto-stellar and UCHII clumps are 0.3452, 0.3861 and 0.2152, respectively. The relatively high detection rate of infall candidates toward UCHII clumps indicates that many UCHII regions are still accreting matter. The peak column densities and masses of the infall candidates, in general, display a increasing trend with progressing evolutionary stages. However, the rough estimates of the mass infall rate show no obvious variation with evolutionary stage. Next, we aim to characterise high-mass clumps with infall motions. We selected 327 clumps from the Millimetre Astronomy Legacy Team 90-GHz (MALT90) survey, and identified 100 infall candidates. Combined with the results of [67], we obtained a sample of 732 high-mass clumps, including 231 massive infall candidates and 501 clumps where infall is not detected. Objects in our sample were classified as pre-stellar, proto-stellar, HII or photo-dissociation region (PDR). The detection rates of the infall candidates in the pre-stellar, proto-stellar, HII and PDR stages are 41.2%, 36.6%, 30.6% and 12.7%, respectively. The infall candidates have a higher H2 column density and volume density compared with the clumps where infall is not detected at every stage. For the infall candidates, the median values of the infall rates at the pre-stellar, proto-stellar, HII and PDR stages are 2.6×10−3, 7.0×10−3, 6.5×10−3 and 5.5×10−3 M⊙ yr−1, respectively. These values indicate that infall candidates at later evolutionary stages are still accumulating material efficiently. It is interesting to find that both infall candidates and clumps where infall is not detected show a clear trend of increasing mass from the pre-stellar to proto-stellar, and to the HII stages. The power indices of the clump mass function (ClMF) are 2.04±0.16 and 2.17±0.31 for the infall candidates and clumps where infall is not detected, respectively, which agree well with the power index of the stellar initial mass function (2.35) and the cold Planck cores (2.0). |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/1715 |
| Collection | 研究生学位论文 射电天文研究室 |
| Affiliation | 中国科学院新疆天文台 |
| Recommended Citation GB/T 7714 | 何玉新. 具有下落运动的大质量分子云团块的搜寻与统计研究[D]. 北京. 中国科学院大学,2016. |
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| File Name/Size | DocType | Version | Access | License | ||
| 何玉新-学位论文.pdf（50612KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
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