Elizabeth Klimek

Ever since Spitzer (1956) predicted the presence of a hot Galactic corona, observational evidence for its existence has continued to grow. With the advent of space based instruments aboard HST, IUE, and FUSE, ultraviolet absorption lines detected along sight lines toward distant background sources have revealed absorption due to a wide variety of metal transitions, such as MgII, AlIII, SiIII, SiIV, CIV, NV, and OVI. The range of ionization stages demonstrates the multiphase nature of the gas in which the Galaxy is embedded. Such detections also emphasize the power of absorption line spectroscopy, which is sensitive to the amount of material along the line of sight. Cosmological simulations are also powerful tools for furthering our understanding of the processes shaping galaxy evolution, as they allow the full 3-D spatial and kinematic behavior of gas to be seen. However, before these simulations can be used as reliable models to help intepret new observations, they must first demonstrate the ability to quantitatively reproduce observations. In the context of the Galactic corona, simulations of star-forming disk galaxies like the Milky Way must be able to reproduce the observed distributions and kinematics of gas as traced by highly ionized species such as OVI. While previous studies have compared simulations to 21-cm emission (cf., Peek et al. 2008)and photometric observations (cf., Guedes et al. 2011), no study has yet compared simulations to absorption line survey observations. We propose to quantitatively compare high resolution cosmological simulations of Milky Way-like galaxies run by the Eulerian Gasdynamics plus N-body Adaptive Refinement Tree (ART) code with the large database of absorption line observations in the literature. We will focus solely on CIV and OVI, two tracers of highly ionized gas for which the most observational data exists. In order to make meaningful comparisons, we will emulate the instruments and methods used by observers as closely as possible. For the simulated galaxies, mock absorption lines will be generated from the point of view of the Solar circle, looking outward into the Galactic halo, and will emulate the resolution, signal-to-noise ratio, pixel sampling, and threshold sensitivity of the spectrographs onboard HST, IUE, and FUSE. The mock spectra will be measured and analyzed in the same manner that absorption line survey data is measured and analyzed by observers. The resulting distributions of column densities, line of sight velocities, and velocity line widths for the simulated galaxies will then be quantitatively compared to observations through a series of statistical tests to determine whether or not the simulated and observed distributions are statistically consistent with each other. We will also compute the covering fractions and determine the scale heights of these ions in the same way that observers do. In the case that there is a significant disparity between measurements made with the simulated and actual observations, we will provide new constraints which theorists will be able to use to refine stellar feedback prescriptions and gas physics on both parsec and kiloparsec scales. In the case that there is good agreement between the simulated and actual observations, we will confirm that the treatment of physical processes such as stellar feedback within the ART code is providing a reasonable description of real galaxies.