Thesis and Dissertation Defenses
Observations and Kinematic Modeling of Neutral Hydrogen in Spiral Galaxies: Implications for Disk-Halo Flows and Accretion
Presented by Laura K. Zschaechner
Recent realizations concerning kinematic measurements of extra-planar layers in nearby galaxies may provide important clues to the origin of such layers and thereby the growth and evolution of galaxy disks. In particular, observations have
shown a decrease in rotation speed with height (lags) in the extra-planar layers of multiple galaxies, leading to various models which attempt to understand this gradient in terms of disk-halo flows and accretion of primordial gas. In this thesis we present deep observations and detailed kinematic models of neutral hydrogen Hi in five nearby, edge-on spiral galaxies (NGC 4244, NGC 4565, NGC 4302, NGC 3044 and NGC 4013) observed with the Very Large Array and the Westerbork Synthesis Radio Telescope. These models provide insight concerning both the morphology and kinematics of HI above and within the disk, especially in terms of their lags. Characterization of the magnitude and radial variation of lags aids in determining whether extra-planar HI originates in the plane of the disk (as described in galactic fountain-type models) or is accreted. In these galaxies we find substantial extra- planar Hi is not ubiquitous, while lags appear to be so. Furthermore, the lags we measure are steeper than those produced by purely ballistic effects, indicating that additional physical effects must be at work. In every (with the exception of NGC 4013) galaxy we model, a radial shallowing of the lag is observed, starting at approximately half of R25, and reaching its lowest magnitude near R25. Combining our sample with results from the literature, we see no clear connection between the presence of extra-planar Hi and star formation, nor do we see any connection between lag magnitude and star formation. Our findings provide constraints for theoretical scenarios which we will describe.
2:30 pm, Monday, July 15, 2013
PAIS-3300, PAIS
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