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 (θA = 3.″7) in the 3.4 mm continuum and in H13CN J = 1 → 0. It is seen nearly edge-on and has a size of ~30,000 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 ≤10,000 yr. The velocity gradient seen in H13CN is consistent with Keplerian rotation. Assuming that the gas is gravitationally bound, the mass of the central object is ~40 M☉. The mass of the continuum "disk" is ≥100 M☉ and has a luminosity of ~104 L☉. H13CN gives a mass of ~400 M☉ for the rotating disk and of ~1000 M☉ for the extended (20'') envelope. Our observations confirm that this is an extremely massive protostar in its earliest stages.