The North-South Asymmetry in the Galactic Rotation Curves

Abstract It is shown that the large scale north-south asymmetry in the galactic rotation curves obtained from observations of neutral hydrogen can be explained as a consequence of non-circular galactic rotation caused by a non-axisymmetric mass distribution in the central region of the Galaxy, i.e., a bar-like structure, and by a radial motion of the local standard of rest at the Sun. In our model the bar is rotating uniformly with an angular velocity 8 km s−1 kpc−1 and the local standard of rest at the Sun is moving with a velocity 3 km s−1 toward the galactic center. The attitude and the elongation of our model bar resemble those of an elliptical dispersion ring proposed by shane (1972) and simonson and mader (1973). No attempt is made to describe how the bar-like structure is formed.