Squaring the circle: making sense of the dusty, magnetized interstellar medium beyond two dimensions

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The interstellar medium (ISM), gas and dust between the stars in the Milky Way, is a vast reservoir from which new stars and planets are being born, and so at the heart of understanding galaxy evolution. With gas phases ranging from cold to hot, molecular to atomic, and neutral to ionized, a dynamically important magnetic field, and turbulent motions, the ISM is in turmoil. The complexity of physical processes and astronomical phenomena stretch our ability to comprehend a stimulating training environment for young researchers on my team, who draw on computational astrophysics, statistics, and data-intensive analysis to apply a broad range of modern physics in very extreme conditions. Using the Planck satellite, we made great progress analysing polarized thermal emission. Dust and associated magnetic fields are seen in projection on the sky, lacking distances and the 3D perspective needed for deep understanding. However, this is about to change, a revolution launched by billions of stellar distances provided by the Gaia satellite. Quantifying dust extinction (scattering plus absorption) of stars locates the dust in distance. To ensure that dust in dense molecular star-forming clouds is probed deeply, my team will make spectral classifications of stars, a novel application of a new multiplexing infrared spectrograph WIFIS. For the best angular resolution, and so 3D distribution, we will produce new maps of dust optical depth based on thermal emission using Herschel. How dust evolves with 3D environment requires new insights. We will focus on a unique set of observations that explicitly measure the same dust at multiple frequencies, aiming for self-consistent dust models. The ratio of optical depth in the submillimetre to extinction in the optical will be calibrated, quantifying the evolution of opacity in 3D. Measuring the amount of scattered light, exploiting the superb wide field sensitivity of the Dragonfly Telephoto Array, compared to thermal emission will provide complementary evidence via albedo and phase function. BLAST-TNG observations of the frequency dependence of the fractional polarization of thermal dust emission compared to interstellar polarization will tightly constrain mixtures of dust components. We are developing more sophisticated 3D models and simulations of the magnetized ISM, both static and dynamic, incorporating how structures evolve in relation to the magnetic field. We have shown that in projection the relative orientation of ISM structures and the magnetic field is parallel in the diffuse medium, but perpendicular at high column density. We will explore dust polarization further with BLAST-TNG at higher angular resolution. Our models ambitiously tackle how the Galactic dust foreground B-mode polarization contaminates the primordial cosmological B-mode signal, grain alignment in dense regions, and the role of the magnetic field in cloud assembly and support.