Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007phdt........26l&link_type=abstract
Proquest Dissertations And Theses 2007. Section 0028, Part 0606 147 pages; [Ph.D. dissertation].United States -- California: Un
Astronomy and Astrophysics
Astronomy
1
Milky Way, Warp, Galaxy, Dense Gas, Spiral Arms, Ngc 6946
Scientific paper
This thesis quantitatively investigates the large-scale distribution and kinematics of gas in the Milky Way and other galaxies. Using the Leiden/ Argentine/Bonn (LAB) survey, I map the vertical structure of the Milky Way in atomic hydrogen. I reduce the complex structure of the warp to three simple Fourier spatial frequencies, and I show that the vertical oscillations known as "scalloping" are local rather than global. I then use unsharp masking to produce perturbed surface density and thickness maps of the outer Milky Way disk. These maps show the presence of spiral arms out to at least 25 kpc from the Galactic center, and demonstrate that overdensities in the surface density are coincident with regions of reduced gas thickness. Using interferometric observations from the VLA Galactic Plane Survey (VGPS) and the Southern Galactic Plane Survey (SGPS), I constrain the rotation curve of the inner Galaxy and its first two vertical derivatives. I use global and local models to find the falloff in the rotation curve from the plane is -22 ± 6 km s -1 kpc - 1 . This result is consistent with the falloff measured in the halos of other galaxies, but is too large to be explained by gravitational physics alone. I also present new observations of dense gas tracers in the central kiloparsec of NGC 6946 made with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). These observations spatially resolve the emission from HCN and HCO+ . I discuss two plausible hypotheses for the distribution of the dense gas.
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