ON THE SPIRAL STRUCTURE OF NGC 5248: AN ANALYTIC APPROACH

摘要

An improved nonlinear asymptotic theory of spiral density waves is developed. It extends the theory developed by Yuan & Kuo to a global theory, not just one limited to the vicinity of the resonance. It can then be applied to the recent high-resolution observations of CO and HST NICMOS of nearby spiral galaxies. As an example, we apply the theory to the nearby grand-design spiral galaxy NGC 5248, which has excellent CO observations in the central regions and exhibits a continuous optical spiral pattern from about 7 kpc to about 100 pc. Using the improved nonlinear asymptotic theory, we confirm the earlier results that the inner two-arm spiral structure of NGC 5248 is driven by a slowly rotating bar potential at the outer inner Lindblad resonance and is a continuation of the outer optical spiral arms. Using the new theory, we calculate the streamlines, surface density, and line-of-sight velocity contours of the bar-driven flow in the central gas disk, and these results are in good agreement with the observations.