Metallicity and Azimuthal Angle Diagnostics of Inflows and Outflows: Interpreting HST Measurements of Circum-Galactic Gas Flows

Project: Research project

Project Details


The regulation of galaxy growth occurs in the circum-galactic medium (CGM), where gas accretion from the cosmic web and galactic outflows interact with one another. Major progress in probing inflows and outflows observationally has been enabled by HST/COS, which has uncovered evidence for a bi-modality in the metallicity distribution of Lyman limit systems (LLSs) associated with CGM gas. The low- and high-metallicity branches have tentatively been identified with inflows and outflows, respectively, but this interpretation remains uncertain because no published simulation has reproduced the observed bi-modality. Complementary measurements using HST imaging have revealed a bi-modality in the azimuthal angle distribution of strong Mg II absorbers relative to the disk of star-forming galaxies. The azimuthal angle bi-modality has also tentatively been interpreted as a way to separate inflows and outflows. We will use a new suite of ultra-high resolution cosmological simulations with resolved ISM physics and stellar feedback (ranging from dwarf galaxies to galaxies more massive than the Milky Way), combined with radiative transfer, to develop inflow and outflow diagnostics motivated by these recent HST observations. By tracking the history of gas elements in our simulations, we will quantify the association of absorbers of different metallicity and azimuthal angle with inflows, outflows, and stripping processes. We will work closely with observational CoIs to compare mock absorption spectra from our simulations to COS data and make several key predictions testable over the next few years.
Effective start/end date12/1/1512/30/19


  • Space Telescope Science Institute (HST-AR-14293.001-A // NAS5-26555)
  • National Aeronautics and Space Administration (HST-AR-14293.001-A // NAS5-26555)


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