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C. Yuan (Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan, ROC), Y.H. Chen (Physics Department, National Taiwan University, Taipei, Taiwan, ROC)
Recent high resolution radio and optical observations have revealed that the majority of the nearby galaxies have a gas-dust disk in the central regions and most of them have central spiral or spiral-bar structure. It is therefore possible for the first time that we can realistically study the relation between the spiral structure and the rotation curve near the center. We use a pair of spiral density waves excited at the outer inner Lindblad resonance (OILR) as a prober to see how they propagate toward the center for various rotation curves. Here are some of the results that we find: (1) Although the rotation curve is often approximated by a rigid-body law near the center by astronomers, spiral waves cannot propagate in the region of rigid-body rotation. The waves are stopped almost immediately at the outer boundary of such a region by a mechanism we call "kinematic damping". (2) Rotation curves which look alike, within the same observation error bars, may have very different spiral patterns. This is because the spiral pattern depends sensitively on the derivative of the rate of the galactic rotation, not the rate itself. (3) Spiral patterns in the central regions are very different between those excited at the OILR and those at the outer Lindblad resonance (OLR). The former which is featured by open spirals is excited by a slow nuclear bar (or by the major bar of the galaxy) and the latter which is featured by tightly wound spirals is excited by a fast nuclear bar. Using this fact, we can deduce the nature of the rotation curve near the center for galaxies without a major bar; tightly wound spirals imply a rapidly rising rotation curve and open spirals imply a slowly rising rotation curve. The work is supported in part by a grant from National Research Council, ROC.
The author(s) of this abstract have provided an email address for comments about the abstract: yuan@asiaa.sinica.edu.tw
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.