Testing the massive disk scenario for IRAS 18089-1732

Investigating in more detail the previously suggested massive disk scenario for the high-mass protostellar object IRAS 18089-1732, we observed the source in the 860 mu m band with the Submillimeter Array in various spectral lines and the submillimeter continuum emission at (sub-)arcsecond spatial resolution. Fifty spectral lines from 18 different species spanning upper-level energy states between 17 and 747 K were detected. One of the assumed best tracers for massive disks, CH3CN, is optically thick and does not allow a further disk investigation. However, the complex molecule HCOOCH3 appears optically thin and exhibits a velocity shift across the central core perpendicular to the emanating outflow. This signature is comparable to well-known low-mass disks and confirms the detection of a massive rotating structure likely associated with the central accretion disk. Assuming equilibrium between centrifugal and gravitational force, the estimated mass for this rotating structure is 16/[sin(2)(i)] M-circle dot (where i is the unknown inclination angle), of the same order as the gas mass derived from the continuum emission. Therefore, in contrast to low-mass disks, a considerable amount of the central gas mass is associated with the rotation, implying that massive disks may not be Keplerian. A temperature estimate based on the CH3CN(19-18) K-ladder results in similar to 350 K; thus, a hot core has already formed in this region. An analysis of the submillimeter continuum emission reveals even at this high spatial resolution only one isolated massive dust core without any detectable companions down to mass limits between 0.2 and 3 M-circle dot (depending on the assumed temperature). Potential implications for the massive cluster formation are discussed. The radial intensity distribution of the core is highly nonsymmetric, outlining the difficulties of density structure investigations based on radial averaging.