Probing Star-Formation and AGN activity with mid-infrared spectroscopy

用中红外光谱探测恒星形成和活动星系核活动

• 批准号: 2597849
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2597849
• 关键词: Probing; Star; Formation; AGN; activity

Strong emission features dominate the spectra of galaxies in the local Universe and out to redshift of 4. These features are attributed to IR fluorescence of Polycyclic Aromatic Hydrocarbons (PAH) molecules upon absorption of UV photons. PAHs are ubiquitous in the Universe and have been used to trace Star Formation activity in star-forming, normal and Active Galactic Nuclei. However, the use of PAHs to trace Star Formation in galaxies is primarily based on empirical relations without much insight about the properties of PAH molecules or, if and how galaxy properties (especially those of the ISM) influence PAH emission. For instance, it is not known how PAHs respond to intense UV/X-ray radiation (as found in the surroundings of an AGN) or how they are affected by UV photo-processing and shocks. As a result, the exact influence of the AGN on PAH emission or how this influence might be mediated by the presence of molecular hydrogen (H2) in the circumnuclear regions of AGN is not yet known. In addition, lack of theoretical models suitable for the harsh environments of galaxies are not widely available.Previous investigations of PAH emission in galaxies utilised spectra from ISO and Spitzer and were limited by poor angular and spectral resolution. With its superbspectral and spatial resolution, wavelength coverage and unprecedented sensitivity especially for low brightness regions, the James Webb Space Telescope is expected to revolutionize PAH research. These new cutting edge observations combined with new theoretical models developed by our group here in Oxford means that we are able to tackle key questions on galaxy evolution. The focus of this DPhil will be on the following questions: 1) what is the role of the AGN on PAH emission in nuclear and circumnuclear regions?2) what is the role of PAHs in regulating a galaxy's star formation efficiency thoughphotoelectric heating and does it change with redshift?3) can we use PAH emission from a distant galaxy to glean information about the conditions of the ISM at those redshifts? To answer these questions the DPhil student will use new observations acquired with the JWST. These observations will be fully analysed with in-house developed software and modelled using our own PAH theoretical models. These are unique computations that we have been able to produce for the very first time. In addition, the DPhil student will investigate a new way to model PAH emission from galaxies by developing `synthetic' MIR spectra based on the combination of theoretical PAH models and real galaxy continua. If successful this technique has the potential to revolutionise the way MIR spectra are interpreted in the future. The outcome of the investigation is bound to establish PAHs as robust Star-Formation Rate indicators applicable not only in local galaxies but all the way to distant galaxies at redshift~7 which will become accessible with the JWST.

强力发射特征主导了本地宇宙中星系的光谱，并占4的红移。这些特征归因于吸收紫外光子后多环芳烃（PAH）分子的IR荧光。 PAH在宇宙中无处不在，已用于在星形成，正常和活跃的银河核中追踪恒星形成活性。但是，使用PAH在星系中追踪星形形成主要是基于经验关系，而没有太多了解PAH分子的特性，或者以及星系性能（尤其是ISM的特性）如何影响PAH的发射。例如，尚不清楚PAHS如何应对强烈的UV/X射线辐射（如在AGN的周围环境中发现），或者它们如何受到UV照相处理和冲击的影响。结果，尚不清楚AGN对PAH发射的确切影响或该影响如何通过分子氢（H2）在AGN的环核区域中介导的影响。此外，缺乏适合星系苛刻环境的理论模型并非广泛可用。对使用ISO和Spitzer的光谱的PAH发射的预防研究受到角度和光谱分辨率的限制。詹姆斯·韦伯（James Webb）太空望远镜有了其出色和空间分辨率，波长覆盖范围和前所未有的敏感性，预计詹姆斯·韦伯（James Webb）太空望远镜将彻底改变PAH研究。这些新的尖端观测与我们小组在牛津开发的新理论模型相结合，这意味着我们能够解决有关银河发展的关键问题。该DPHIL的重点将放在以下问题上：1）AGN在核和周围区域的PAH排放中的作用是什么？2）PAH在调节银河系的星形形成效率液位效率中的作用是什么作用？为了回答这些问题，Dphil学生将使用JWST获得的新观察结果。这些观察结果将通过内部开发的软件进行全面分析，并使用我们自己的PAH理论模型进行建模。这些是我们第一次能够制作的独特计算。此外，DPHIL学生将根据理论PAH模型和真实的Galaxy Continua的组合来开发“合成” mir光谱来研究一种新的方法来建模星系中的PAH发射。如果成功的话，该技术有可能彻底改变MIR光谱的解释方式。调查的结果必将确立PAH作为可靠的恒星形成率指标，不仅适用于局部星系，而且一直适用于Redshift〜7处的遥远星系，这将与JWST访问。