Distances to most star forming regions are determined using kinematics,
through the assumption that the observed radial velocity arises from the motion
of the source with respect to the Sun resulting from the differential rotation
of Galaxy. The primary challenge associated with the application of this
technique in the inner Galaxy is the kinematic distance ambiguity. In this
work, we aim to resolve the kinematic distance ambiguity towards a sample of
6.7 GHz methanol masers, which are signposts of the early stages of massive
star formation. We measured 21 cm HI absorption spectra using the Very Large
Array in C and CnB configurations. A comparison of the maximum velocity of HI
absorption with the source velocity and tangent point velocity was used to
resolve the kinematic distance ambiguity. We resolved the distance ambiguity
towards 41 sources. Distance determinations that are in conflict with previous
measurements are discussed. The NE2001 spiral arm model is broadly consistent
with the locations of the star forming complexes. We find that the use of
vertical scale height arguments to resolve the distance ambiguity can lead to
erroneous classifications for a significant fraction of sources.Comment: Accepted by Astronomy & Astrophysic
