Astronomical imaging spectroscopy at far-infrared wavelengths

远红外波长的天文成像光谱

• 批准号: RGPIN-2016-06551
• 负责人: Naylor, David
• 金额: $ 7.07万
• 依托单位: University of Lethbridge
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=709253
• 关键词: Astronomical; imaging; spectroscopy; far; infrared

Approximately half of the radiant energy emitted by the universe falls in the far-infrared (FIR) spectral range (301000 µm) for two reasons: the first is that sources in the distant universe, galaxies in the local universe, or protostars in our own galaxy are often shrouded in dust and gas. The dust efficiently scatters and absorbs shorter wavelength radiation, which is subsequently re-radiated at longer wavelengths, both as continuum (dust) and line (ions, atoms, molecules) emission. The second reason is that distant galaxies do not decrease in IR brightness with increasing distance, because their emission is redshifted into the IR. Most of the FIR is inaccessible from the ground due to atmospheric absorption. Moreover, space borne instruments must operate at ~ 4 K to minimize their self-emission, which would otherwise dominate the weak astronomical signal. In previous FIR missions cooling was achieved by placing the entire telescope in a cryostat, limiting the diameters of primary mirrors to ~60 cm and resulting in relatively low spatial resolution. The Herschel Space Observatory broke this trend by employing a 3.5 m diameter passively cooled primary mirror located outside of the instrument payload, the instrument suite being cooled to ~4K. This design provided a major advance in spatial resolution and sensitivity, however, the latter remained limited by photon noise from the relatively warm (~80K) telescope. Potential gains in sensitivity of 2 -3 orders of magnitude exist by actively cooling large aperture telescopes as proposed for the ESA/JAXA SPICA mission. However, to realize these gains, the noise performance of the instruments themselves must be understood to a corresponding higher degree. This proposal has two components, the first is to continue to use data from Herschel/SPIRE in the study of the interstellar medium and the earliest stages of star formation, the time when molecular clouds fragment into cold and dense gravitationally bound cores. Starless cores can be probed by studying their thermal (continuum) emission, which provides information about the dust properties, and their line emission (or absorption), which provides information on the chemistry in these regions. Together they provide a unique window into the initial conditions of protostellar collapse. With its broad spectral coverage and intermediate resolution SPIRE is well suited to this task. The second component is to develop and evaluate the performance of a prototype of the spectrometer proposed for the SPICA/SAFARI instrument. A recently commissioned, large volume, low background, test facility cryostat will be used to study optical and thermal properties of key components of the spectrometer such as etalons, mechanisms and metrology. The ability to evaluate the performance of an integrated system at cryogenic temperatures will position Canada to be a partner of choice in future FIR space astronomy missions.

宇宙发射的辐射能大约有一半落在远红外 (FIR) 光谱范围 (301000 µm)，原因有两个：第一是遥远宇宙中的辐射源、本地宇宙中的星系或我们自己星系中的原恒星通常笼罩在尘埃和气体中。灰尘有效地散射和吸收较短波长的辐射，随后以连续谱（灰尘）和线（离子、原子、分子）发射的形式以较长波长重新辐射。第二个原因是遥远星系的红外亮度不会随着距离的增加而降低，因为它们的发射红移到红外中。 由于大气吸收，大部分远红外线无法从地面到达。此外，星载仪器必须在约 4 K 的温度下运行，以最大限度地减少其自发射，否则自发射将主导微弱的天文信号。在之前的 FIR 任务中，冷却是通过将整个望远镜放置在低温恒温器中来实现的，将主镜的直径限制在约 60 厘米，从而导致空间分辨率相对较低。赫歇尔空间天文台打破了这一趋势，采用了位于仪器有效载荷外部的直径 3.5 m 的被动冷却主镜，仪器套件被冷却至约 4K。这种设计在空间分辨率和灵敏度方面取得了重大进步，但是，后者仍然受到来自相对温暖（~80K）望远镜的光子噪声的限制。按照 ESA/JAXA SPICA 任务的建议，主动冷却大孔径望远镜可以将灵敏度提高 2 -3 个数量级。然而，为了实现这些增益，必须相应地更高程度地了解仪器本身的噪声性能。 该提议有两个组成部分，首先是继续使用 Herschel/SPIRE 的数据来研究星际介质和恒星形成的最早阶段，即分子云分裂成寒冷而致密的引力束缚核心的时间。无星核心可以通过研究它们的热（连续）发射来探测，这提供了有关尘埃特性的信息，也可以研究它们的线发射（或吸收），这提供了有关这些区域的化学信息。它们共同为了解原恒星坍缩的初始条件提供了一个独特的窗口。 SPIRE 具有广泛的光谱覆盖范围和中等分辨率，非常适合这项任务。 第二个部分是开发和评估为 SPICA/SAFARI 仪器提议的光谱仪原型的性能。最近投入使用的大容量、低背景测试设施低温恒温器将用于研究光谱仪关键部件（如标准具、机构和计量）的光学和热性能。评估集成系统在低温下的性能的能力将使加拿大成为未来远红外空间天文学任务的首选合作伙伴。