Testing the Accuracy of the Tangent Point Method for Determining the Milky Way’s Inner Rotation Curve

Abstract

Abstract The tangent point method (TPM) is commonly used to calculate the rotation curve of the inner portion of the Milky Way, relying on the assumption that along one line of sight, the point tangent to the Galactic center is the point where the observed radial velocity is an extremum. This work compares rotation curves derived from the TPM, using neutral hydrogen gas data, and direct measurements of stellar positions and velocities from the Gaia Satellite. The Gaia data indicate that the rotation curve based upon stellar kinematics is much shallower than that previously reported based on the TPM, especially in the inner regions of the Galaxy. Additionally, based on stellar kinematics, the locations of the extremum radial velocities and tangent points often differ. While these results are consistent with previously published simulations, future data from the Gaia satellite will allow for further confidence in determining an accurate rotation curve.