A Kpc Scale Molecular Wave in the Inner Galaxy: Feather of the Milky
  Way?
  We report the discovery of a velocity coherent, kpc-scale molecular structure
towards the Galactic center region with an angular extent of 30deg and an
aspect ratio of 60:1. The kinematic distance of the CO structure ranges between
4.4 to 6.5 kpc. Analysis of the velocity data and comparison with the existing
spiral arm models support that a major portion of this structure is either a
sub-branch of the Norma arm or an inter-arm giant molecular filament, likely to
be a kpc-scale feather (or spur) of the Milky Way, similar to those observed in
nearby spiral galaxies. The filamentary cloud is at least 2.0 kpc in extent,
considering the uncertainties in the kinematic distances, and it could be as
long as 4 kpc. The vertical distribution of this highly elongated structure
reveals a pattern similar to that of a sinusoidal wave. The exact mechanisms
responsible for the origin of such a kpc-scale filament and its wavy morphology
remains unclear. The distinct wave-like shape and its peculiar orientation
makes this cloud, named as the Gangotri wave, one of the largest and most
intriguing structures identified in the Milky Way.
