Collaborative research: Multiscale physics and feedback in real and simulated circumgalactic gas over cosmic time

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Although scientists know a great deal about galaxies in the Universe, less is known about the gas that surrounds them all and especially about the interplay between this reservoir of material and the visually stunning regions so familiar from telescope images. This truly unique study covers an enormous range in physical scale, from the smallest observable clouds to clusters of galaxies, to show the real dynamical interaction between the visible galaxies and their surroundings. Junior researchers and students will learn how to run and to interpret state-of-the-art numerical simulations, and how to carry out data mining on existing observation archives.The circum-galactic medium (CGM) is the diffuse gas surrounding galaxies that acts as a fuel tank, waste dump, and recycling center. Recent discoveries show that the CGM is dynamic, rapidly evolving, has significant mass, and plays a key role in determining the mass, shape, and star-forming properties of galaxies. This project applies a new combination of data with models to examine the role of the CGM in galaxy evolution over seven orders of magnitude in physical scale, which is required to truly understand its conditions and kinematics. The data will be mined from existing archives, and the models will come from a suite of state-of-the-art numerical simulations. The rigorous comparison will use a toolkit developed by this team to produce mock datasets from simulations, which can then be analyzed in concert with the real data. This work should solve several puzzles: 1) although abundant in chemical elements, the dense CGM is not as well-mixed as predicted; 2) galaxies have massive reservoirs of metal-rich gas that should have an extremely short cooling time; 3) the cool CGM is too diffuse to be in pressure equilibrium with a hot galactic corona; and 4) there is just as much cool, neutral gas in the CGM of passive galaxies as in that of star-forming galaxies, so that this gas can be neither fuel for, nor a by-product of, star formation. This understanding can only be gained by a breakthrough in understanding physics at the scales of the smallest individual clouds that observations can detect, which is not possible except by using multi-scale simulations rigorously coupled to data. The study will reveal the physical state of CGM gas, constrain the timescales over which CGM clouds evolve, and determine the mass flow rates and total masses moving in and out of galaxies.These results will be the focus of outreach talks by all team members to the diverse communities in the areas around the different institutions involved. The project will involve junior scientists in front line research, especially targeting under-represented students, and contributing to mentoring skills amongst the intermediate-level researchers. It will also support development of a new planetarium show that includes visualized hydro-dynamical simulations of the gas in galaxies.