Rotation of the disc in M 17

Position-velocity diagram revealing the rotation of the disc. It is derived from a cut along the major axis of the disc, using the IRAM Plateau de Bure interferometer. For comparison, the theoretically expected position-velocity curve for an edge-on disc around a star of 15 solar masses is shown, the outer part of which (radii larger than about 15,400 AU) is in Keplerian rotation while its inner part is modeled as a rigid rotator.