An Analysis of the Gas Dynamics of Illustristng Halos

The circumgalactic medium (CGM) is an envelope of gas surrounding galaxies. This envelope can extend to the virial radius and is mostly made of diffuse, hot gas in equilibrium with denser, cooler clouds. This gas acts as reserve fuel for star formation; understanding the processes affecting this medium is key to understanding quenching, and galactic evolution in general. In this dissertation I present the results of my work with the IllustrisTNG (TNG) hydrodynamic simulation. In order to explore the connection between central galaxy activity and the motion of gas in the CGM I calculate the average distribution and dynamics of mass and metal in stacked TNG halos. The majority of gas has low radial velocity, but CGM dynamics are primarily determined by high radial velocity gas. Radial profiles of metallicity, mass flow, metal flow, and other properties tend be divided into an inner and outer region along the same normalized radius, suggesting a scale for the inner vs outer CGM. The sample is divided into into low, medium, and high mass brackets, and further divide by feedback type into low feedback (LFB), star-forming (SF), kinetic mode (KM) and star-forming kinetic mode (SFKM) halos. There are key differences in the feedback such as the reach and breadth of the effects, with star formation having a much more localized effect on the CGM, while kinetic feedback causes large changes in flow at all angles within the virial radius. Although halo mass is generally considered a primary driver of halo differences, I show that the motion of the CGM is correlated more strongly with feedback type than with mass. In general each type of galaxy exhibits a distinct behavior across our mass range: in the absence of outward pressure from outflows, LFB halos are rapidly accreting pristine gas; SF feedback expels metals from the inner regions and enrich the CGM out to the virial radius; KM feedback causes intense outflows that remove gas and metals from the CGM entirely, and enrich the IGM; and SFKM halos have features of both SF and KM halos, and are rare in TNG because KM feedback is also the primary quenching mechanism. I show that apparent differences with halo mass are due to changing feedback demographics, but that each feedback type has consistent behavior regardless of mass. There is a complex relationship between quenching and morphology. At high mass all SFKM halos are disks despite recieving more KM energy than quenched spheroids, implying disks are more resistant to quenching. Hydrodynamic simulations have different methods of determining halo membership, or deciding where a halo ends. The friends-of-friends algorithm used in TNG results in a collection of non-member particles, called "outer fuzz" which are not assigned to any halo. This gas is analogous to the IGM, but it also permeates the virial radius of halo, constituting～15% of the outer CGM mass. Accessing data on this gas is not straightforward, and it is often neglected in studies of halos. We quantify the effects of this gas and find that it is impactful on the dynamics of massive KM halos, and should be included in studies of objects with M ≳ 10^12 M⊙. I explain my contribution to the Circumgalactic Dictionary, which will allow observers to match spectra to the properties of simulated gas with similar spectra. I created a new absorption line database and a data structure that combines spectral data, gas properties, and halo and subhalo properties, and geometric data for each line of sight. This tool will allow us to better connect simulations to observations.