NGC 7538S - A high-mass protostar with a massive rotating disk

We report the detection of a massive rotating disk around the high-mass Class 0 candidate NGC 7538S. The disk is well resolved with the Berkeley-Illinois-Maryland Association array (theta(A) = 3.7) in the 3.4 mm continuum and in (HCN)-C-13 J = 1 --> 0. It is seen nearly edge-on and has a size of similar to30,000 AU. A young, powerful outflow perpendicular to the rotating disk is mapped in SiO J = 2 --> 1 and HCO+ J = 1 --> 0. The dynamical age of the outflow is less than or equal to10,000 yr. The velocity gradient seen in (HCN)-C-13 is consistent with Keplerian rotation. Assuming that the gas is gravitationally bound, the mass of the central object is similar to40 M.. The mass of the continuum disk is greater than or equal to100 M. and has a luminosity of similar to10(4) L. (HCN)-C-13 gives a mass of similar to400 M. for the rotating disk and of similar to1000 M. for the extended (20) envelope. Our observations confirm that this is an extremely massive protostar, in its earliest stages.