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Dr. Nikole Nielsen

The focus of my research is to understand how galaxies form and evolve by studying the properties and motions of gas in the circumgalactic medium (CGM), a massive and diffuse reservoir of gas surrounding galaxies. I study the baryon cycle, or the flow of gas into and out of galaxies, as cosmological simulations have shown it is vital in regulating galaxy evolution and building up the CGM. Quasar absorption lines due to light from a background quasar piercing the CGM of a foreground galaxy are a powerful tool to obtain detailed gas properties such as the ionization balance, chemical content, density, temperature, and kinematics. By comparing the absorption to the host galaxy properties (color, redshift, orientation, etc.), I determine whether the gas being probed is likely accreting from the intergalactic medium or the CGM (recycled accretion), outflowing from star formation in the galaxy, or being tidally stripped from merging satellite galaxies. This allows me to constrain the role that the baryon cycle plays in galaxy evolution and to test predictions from the simulations. My main source of data is the MgII Absorber-Galaxy Catalog, or MAGIICAT, and contains both MgII doublet absorption and galaxy data for 182 absorber-galaxy pairs. I am involved in expanding the catalog of absorber-galaxy pairs to absorption lines tracing higher temperature gas and therefore different baryon cycle processes.

Phone   +61 3 9214 5887
Fax   +61 3 9214 8797
Office   AR304
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