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Rotation curves are often used to estimate the mass distribution of spiralgalaxies, assuming circular rotation of disks. However, non-circular motionscaused by a non-axisymmetric gravitational potential, such as a stellar bar,may disturb the velocity field, resulting in errors in mass estimation,especially in the central regions of galaxies, because the line-of-sightvelocity depends on the viewing angles in a non-axisymmetric flow. Observingrotation curves of edge-on galaxies in time-dependent numerical simulationsfrom different viewing angles, we obtain errors in the estimation of galacticmass from the rotation curves. In the most extreme case, the ellipticity of gasorbits is as high as 0.8 in the central regions, even if the bar potential isweak. When rotation curves are defined as the highest velocity envelope ofposition-velocity diagrams, the mass estimated from the rotation curves islarger than the true mass by a factor of five for 15% of the viewing angles,and the ratio between the apparent mass and true mass is less than six for anyviewing angle. The overestimation in mass occurs more frequently than theunderestimation.Comment: 11 pages, 10 figures, accepted by A&

Intrinsic errors of the central galactic mass derived from rotation curves under the influence of a weak non-axisymmetric potential