Modeling Non-Circular Motions in Disk Galaxies: Application to NGC 2976

Abstract

We present a new procedure to fit non-axisymmetric flow patterns to 2-D velocity maps of spiral galaxies. We concentrate on flows caused by bar-like or oval distortions to the total potential that may arise either from a non-axially symmetric halo or a bar in the luminous disk. We apply our method to high-quality CO and Halpha data for the nearby, low-mass spiral NGC 2976 previously obtained by Simon et al., and find that a bar-like model fits the data at least as well as their model with large radial flows. We find supporting evidence for the existence of a bar in the baryonic disk. Our model suggests that the azimuthally averaged central attraction in the inner part of this galaxy is larger than estimated by these authors. It is likely that the disk is also more massive, which will limit the increase to the allowed dark halo density. Allowance for bar-like distortions in other galaxies may either increase or decrease the estimated central attraction.Comment: 12 pages, 6 figures, accepted for publication in ApJ. v2: minor changes to match proofs. For version with high-resolution figures, see http://www.physics.rutgers.edu/~spekkens/papers/noncirc.pd