大質量恆星的形成，不像它的低質量的兄弟姐妹，仍然不理解它的環境，形成機理和演化序列的條款。紅外暗雲（IRDCs），密集與黑暗的剪影對明亮的銀河背景，被認為是大質量恆星和集群的形成，是寒冷，密集，大規模足夠懷有巨大的原恆星在某些時候他們的生活的搖籃。然而，由於這些對象的遙遠和不透明性，高角分辨率無線電和紅外觀測需要解決的IRDC芯，其中所述恆星形成發生。以往的研究表明IRDCs的巨大差異，從茂密的靜態風雲恆星形成的邊緣相對發展地區，大量嵌入原恆星駕駛流出並形成HII區。IRDC演變的各種示踪劑已經提出，旨在建立IRDC多樣性和進化序列的連貫的畫面。嵌入式原恆星加熱的環境的存在可以從IRDC測量溫度來推斷核心，具有光度追踪其演化階段。我們提出的進化示踪劑的分析九相對靜止紅外烏雲密布，同時使用單天線觀測和可用紅外數據。我們發現下降趨勢N2H+與從氨的氣體溫度，灰塵溫度，N2H+線寬和熱光度的氘分離。我們的研究結果表明最早的大質量恆星前體的一般行為，並建議使用N2H+氘分餾在大質量恆星形成區的化學時鐘。

Massive star formation, unlike its lower mass sibling, is still not understood in terms of its environment, formation mechanism and evolutionary sequence. Infrared dark clouds (IRDCs), dense and dark silhouettes against bright Galactic background, are thought to be the cradles of massive star and cluster formation, being cold, dense, and massive enough to harbour massive protostars at some point of their life. However, due to distant and opaque nature of these objects, high-angular resolution radio and infrared observations are required to resolve the IRDC cores, where the star formation takes place. Previous studies show great diversity of IRDCs, ranging from dense quiescent clouds on the verge of star formation to relatively evolved regions with embedded massive protostars driving outflows and forming HII regions. Various tracers of IRDC evolution have been proposed, aiming to establish a coherent picture of IRDC diversity and evolutionary sequence. A presence of an embedded protostar heating up its environment could be inferred from measuring temperature of the IRDC core, with luminosity tracing its evolutionary stage. We present an analysis of evolutionary tracers in nine relatively quiescent infrared dark clouds, using both single-dish observations and available infrared data. We find decreasing trend in deuterium fractionation of N2H+ vs. gas temperature derived from ammonia, dust temperature, N2H+ line width and bolometric luminosity. Our findings suggest a general behavior of earliest massive star precursors and suggest the use of deuterium fractionation of N2H+ as a chemical clock in massive star-forming regions.

Table of Contents i
List of Figures iii
List of Tables vii
1 Introduction
1.1 Massive Star Formation
1.1.1 Infrared Dark Clouds as Host Sites for Massive Star Formation
1.1.2 Chemistry in IRDCs
2 Observations and Data Reduction
2.1 Data from the literature
2.2 Nobeyama 45m observations
2.3 Herschel observations
2.3.1 PACS data
2.3.2 SPIRE data
3 Data Analysis
3.1 Continuum and line fitting
3.1.1 Gas temperature
3.1.2 Herschel SED fitting
4 Results and Disscussion
4.1 Dust and gas temperatures
4.2 Deuterium fractionation as IRDC core evolutionary tracer
4.3 Conclusions
Appendices
A PACS Zero Level and Gain Corrections
B Temperature and Column Density Maps
C Source SED profiles
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