Development of Sub-Millimetre Heterodyne Array & Probing the Interstellar Medium of Nearby Galaxies with JWST and ALMA

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This D.Phil. programme is comprising two complementary science topics: A focus on the development of the sub-millimetre quantum detector, and an observation project utilising mid-infrared (MIR) data from JWST and ALMA.The physical and chemical conditions in star-forming regions can be determined by observing at millimetre and sub-millimetre wavelengths, where a host of atomic, ionic and molecular lines can be found. In recent years, spectroscopic and interferometric observations of these lines have refined our knowledge of the gas dynamics and kinematics of nearby and distant galaxies, as well as enabling the first direct detection of black hole images. These observations have only been possible because of the extraordinary characteristics of near quantum-noise-limited Superconductor-Insulator-Superconductor (SIS) heterodyne receivers. SIS mixers are used routinely on observatories such as the Northern Extended Millimetre Array (NOEMA), the Atacama Large Millimetre/sub-millimetre Array (ALMA), and the Herschel space observatory, to name a few, enabling numerous observations of faint objects with high spectral and spatial resolution. However, there is a major limitation in utilising SIS receivers for near future astronomical observation, either ground-based or space-borne.Traditional high spectral resolution observations demand excessive telescope time. This hampers important scientific programs, especially when complementing large-area continuum mapping data done by e.g., bolometric arrays on Herschel which lack of dynamic and kinematic information, or science that require large area high spatial and spectral resolution. Improving mapping speed entails increasing the number of detectors and/or enhancing sensitivity. However, most existing sub-mm instruments fall short of reaching the ultimate quantum limit, crucial for imaging high-z galaxies and black holes. Additionally, these instruments often possess a limited number of spatial pixels, making mapping large structure within the Galactic plane and nearby galaxies a formidable challenge.A new generation of ultra-sensitive wide-field infrastructure is now required e.g., the planned ground-based (e.g., AtLAST, LST) and space-based (e.g., NASA Probe) telescopes, that are expected to be equipped with large pixel count heterodyne arrays (~103 pixels) and must be built whilst retaining extraordinary levels of individual-pixel sensitivity. It is only possible to plan the construction of large instruments with confidence, once the needed technology has been developed to high TRL, including smaller-scale demonstration on existing telescopes. This D.Phil. project therefore aim to address these challenges by developing a small-pixel count sub-millimetre heterodyne array, involving advancing techniques at every stage, making them modular and array-able, with an eye towards enabling the future deployment of kilo-pixel receivers. The project targets to demonstrate the technologies by developing a dual-polarisation sub-millimetre heterodyne demonstrator, which would retain the full astronomical signal strength and preserve the polarisation information. For the scientific observation part, the student will focus on an investigation of the Interstellar Medium of a sample of nearby galaxies using data from the James Webb Space Telescope (JWST) Mid-Infrared Spectrometer (MIRI) and the Atacama Large Millimetre Array (ALMA). The advent of JWST has provided us with unprecedented sensitivity and spatial resolution to enable studies of the properties of the ISM in a spatially resolved manner in galaxies near and far. The project will focus on a sample of nearby galaxies and will examine, for the first time, element abundances based on mid-infrared (MIR) ionic lines which are unaffected by temperature dependencies and therefore will deliver robust estimates of metallicity gradients. Furthermore, the student will compare the distribution of molecular gas (often used to trace the raw ma