Computer Science
Scientific paper
Jul 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt........18w&link_type=abstract
Thesis (PHD). RUTGERS THE STATE UNIVERSITY OF NEW JERSEY - NEW BRUNSWICK , Source DAI-B 59/01, p. 261, Jul 1998, 140 pages.
Computer Science
5
Disks, Ngc 4123
Scientific paper
We present observations and simulations of the structure and dynamics of NGC 4123, a typical barred spiral galaxy, and of the Milky Way. We use fluid-dynamical simulations of gas flow to constrain the properties of these galaxies. We construct models for the structure of each galaxy, derive the gravitational potential for each model, and compute the gas flow pattern in that potential. By comparing the simulated gas flow pattern to match observational data on the gas kinematics, we can discriminate between the input models. For NGC 4123, we use near-infrared I-band imaging and an extended 21 cm H I rotation curve to construct models composed of a luminous disk and a dark halo. The models are parametrized by the mass-to-light ratio (M/L) of the stellar disk, and the bar pattern speed. We compare the simulations to a 2-D velocity map obtained from Fabry-Perot spectroscopy. Models with a near-maximum disk with M/L of 2 to 2.5, and with fast-rotating bars, reproduce the data well. Sub-maximal disks and slow bars are ruled out. For the Milky Way, we construct analytical models for a barred potential and compare simulations to H I data published by Liszt & Burton. We exhibit a model which matches the observed extreme-velocity contour of the H I longitude-velocity diagram. This model has a fast-rotating bar of length 3.6 kpc and best fits the data when viewed at an angle of 34o to the bar major axis. The model is not unique, but we argue that the real Galactic potential is likely to resemble it in certain aspects such as bar size, viewing angle, bar pattern speed, and existence of an inner Lindblad resonance. We conclude that both NGC 4123 and the Milky Way must have fast-rotating bars, and disks which dominate the mass in the inner regions of the galaxy. The latter result is especially true for NGC 4123, whose disk must be 90-100% of the 'maximum disk' value. This contradicts a number of recent claims for 'universal' relations that imply disk galaxies must be embedded in very massive dark halos which dominate over the disks.
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