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The Angular Momentum of the Circumgalactic Medium and its Connection to Galaxies in the Illustris and TNG Simulations

Presentation #106.05D in the session Evolution of Galaxies I.

Published onJun 29, 2022
The Angular Momentum of the Circumgalactic Medium and its Connection to Galaxies in the Illustris and TNG Simulations

A galaxy’s angular momentum is known to be correlated with its morphology: at a given mass, spiral galaxies have higher angular momenta than elliptical galaxies. A galaxy’s angular momentum is also largely set by its formation history: in particular, how much gas and the kinematic state of the gas that both accretes onto it and is expelled in galactic outflows from AGN and supernovae. All gas inflowing to and outflowing from the galaxy interacts with gas in the region surrounding the galaxy called the circumgalactic medium (CGM), which means at a fundamental level, the CGM controls the angular momentum of the galaxy. Therefore, to really understand the origins of galactic angular momentum, it is necessary to understand the angular momentum of the CGM itself. First, to understand how present-day galaxies acquire their observed angular momentum, I analyze the evolution of the angular momentum of Lagrangian gas mass elements from the Illustris simulation as they accrete onto dark matter halos, condense into Milky Way-scale galaxies, and join the z = 0 stellar phase of those galaxies. I find that physical feedback from the galaxy is essential in order to produce reasonable values of galactic angular momentum, and that most of the effects of this feedback occur in the CGM. I then characterize the angular momentum distribution and structure within the CGM of simulated galaxies over a much larger range of halo masses and redshifts, with the goal of determining if there are common angular momentum properties in CGM populations. I indeed find that the angular momentum of the CGM is larger and better aligned around disk galaxies that themselves have high angular momentum. I also identify rotating structures of cold gas that are generally present around galactic disks. Next, I perform a comparison to observations from the MEGAFLOW survey of cold CGM gas by generating synthetic observations of cold CGM gas around star-forming galaxies from IllustrisTNG and measuring the kinematic signatures of that gas. I show that IllustrisTNG produces rotating gas in the CGM consistent with observations to a high degree. Finally, I present unpublished work where I examine angular momentum evolution in the CGM on much finer timescales than can be resolved with the cosmological simulations I have used thus far. Preliminary results suggest that gas can experience large changes in angular momentum very quickly, and that these changes may be connected to corresponding changes in temperature.

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