Studying Metals in the Circumgalactic Medium by Post-Processing Cosmological Galaxy Simulations
In recent decades, cosmological simulations have played an increasing role in the expert understanding of galaxy formation, but while simulations have improved dramatically, many parameters such as the strength of stellar and supernova feedback are not well determined. The circumgalactic medium (CGM), the gas outside of the galaxy disc but within the dark matter halo, could be an effective probe of feedback models due to its high ionization level and low density. However, since the CGM does not form stars and is usually detected in absorption spectra, instead of simulated telescope image comparisons, a more specialized methodology is needed. This work analyzes the CGM of many simulated galaxies using the random sampling of sightlines throughout a spherical volume surrounding them, emulating absorption spectra. We determine each sightline using two points: the starting location is chosen uniformly over the surface of the sphere and the midpoint is uniformly distributed throughout the bulk of a smaller concentric sphere. We project along this line of sight and use ionization calculation software TRIDENT to determine the column densities of ions situated in the line. Since we can make a large number of individual sightlines, many statistical properties can be examined, covering the full spectrum of redshifts, star formation histories, masses, and other macroscopic parameters of the simulated galaxies. These properties can be directly compared to observed absorption data, and can therefore help constrain the parameters of these simulations and either improve confidence in their predictions or determine what physical models need to be adjusted.