High Frequency Channel for CHAI

基于我们为科隆大学的Herschel和索菲亚等主要观测设施开发传统仪器的经验，我们目前正在建造Chajnantor外差阵列仪器（CHAI），将部署在智利北方Cerro Chajnantor山顶CCAT天文台的Fred Young亚毫米望远镜（FYST）上，海拔5600米。FYST是一种新型的6米口径望远镜，计划于2024年看到第一束光。它将能够在亚毫米波长进行高灵敏度的宽视场观测。它的仪器将涉及从恒星的形成和银河系及附近星系星际介质的演变到早期宇宙和宇宙学中的星系等科学课题。CHAI特别重要，因为它将是唯一一台通过其多像素外差光谱仪提供高分辨率光谱的仪器，该光谱仪在第一次光照时在其低频通道（LFA）中覆盖400至490 GHz的观测频率。因此，25%的可用观测时间将分配给CHAI及其科学案例，这在CCAT联盟合作伙伴协议中得到保证。我们在这里的目标是通过在800 GHz大气窗口中为CHAI添加高频通道（HFA）来更好地利用CCAT观测站的优良大气条件。通过同时观测LFA和HFA，该仪器的性能将翻倍，再加上其在这些频率下的光谱学的前所未有的映射速度和灵敏度。更重要的是，第二个频率窗口提供了独特的新科学，这是完全解决CCAT天文台关键计划GEco（银河生态项目）中定义的研究课题所必需的。这次巡天旨在研究银河系和附近星系星际介质中的物质循环，从云的聚集到其中的细丝、枢纽和核心的形成，最终形成恒星，而恒星反过来又提供恒星反馈。完整的科学案例需要高频观测，因为它们不仅为我们的低频观测提供了宝贵的信息，而且还为其他大规模调查以及我们对星际介质中结构形成及其演变的理解提供了宝贵的信息。该提案的主要目标是确保为建造CHAI HFA提供资金，从而实现并收获在从DFG和合作伙伴资源中获得FYST望远镜资金时所设想的科学。

Building on our experience with developing legacy instruments for major observing facilities like Herschel and SOFIA at University of Cologne, we are currently building the Chajnantor Heterodyne Array Instrument (CHAI), to be deployed on the Fred Young Submillimeter Telescope (FYST) of the CCAT observatory on top of Cerro Chajnantor in northern Chile at 5600 m altitude. FYST is a novel 6 m aperture telescope scheduled to see first light in 2024. It will enable highly sensitive wide field observations at submillimeter wavelengths. Its instruments will address science topics ranging from the formation of stars and the evolution of the interstellar medium in the Milky Way and nearby galaxies to galaxies in the early universe and cosmology. CHAI is of particular importance, since it will be the only instrument providing high resolution spectroscopy through its multi-pixel heterodyne spectrometer covering observing frequencies from 400 to 490 GHz in its low frequency channel (LFA) at first light. Accordingly, 25% of the available observing time will be allocated to CHAI and its science cases, as guaranteed in the CCAT consortium partner agreement. We here aim to even better exploit the excellent atmospheric conditions at the CCAT observatory site by adding a high frequency channel (HFA) to CHAI, operating in the 800 GHz atmospheric window. Through simultaneous observation of the LFA and HFA, the performance of the instrument will be doubled, on top of its already unprecedented mapping speed and sensitivity for spectroscopy at these frequencies. More importantly, the second frequency window gives access to unique new science, which is necessary to fully address the research topics defined in the CCAT observatory key program GEco, the Galactic Ecology project. This survey is designed to study the matter cycle in the interstellar medium of the Milky Way and nearby galaxies from the assembly of clouds to the formation of filaments, hubs and cores within them, and eventually stars, which in turn provide stellar feedback. The full science case requires the high frequency observations as they give invaluable information for the interpretation not only of our low frequency observations, but also other large scale surveys and our understanding of the formation of structures in the interstellar medium and their evolution. The key objectives of this proposal are to secure funding to build the CHAI HFA, and thus, to enable and harvest the science that has been envisioned when securing the funding for thr FYST telescope from the DFG and partner resources.