2007A&A...468.1045B

Hot molecular cores are an early manifestation of massive star formation where the molecular gas is heated to temperatures >100K undergoing a complex chemistry. One wants to better understand the physical and chemical processes in this early evolutionary stage. We selected the prototypical hot molecular core G29.96-0.02 being located at the head of the associated ultracompact HII region. The 862 µm submm continuum and spectral line data were obtained with the Submillimeter Array (SMA) at sub-arcsecond spatial resolution. The SMA resolved the hot molecular core into six submm continuum sources with the finest spatial resolution of 0.36''x0.25'' (∼1800AU) achieved so far. Four of them located within 7800(AU)² comprise a proto-Trapezium system with estimated protostellar densities of 1.4x10⁵protostars/pc³. The plethora of ∼80 spectral lines allows us to study the molecular outflow(s), the core kinematics, the temperature structure of the region as well as chemical effects. The derived hot core temperatures are of the order 300K. We find interesting chemical spatial differentiations, e.g., C³⁴S is deficient toward the hot core and is enhanced at the UCHII/ hot core interface, which may be explained by temperature sensitive desorption from grains and following gas phase chemistry. The SiO(8-7) emission outlines likely two molecular outflows emanating from this hot core region. Emission from most other molecules peaks centrally on the hot core and is not dominated by any individual submm peak. Potential reasons for that are discussed. A few spectral lines that are associated with the main submm continuum source, show a velocity gradient perpendicular to the large-scale outflow. Since this velocity structure comprises three of the central protostellar sources, this is not a Keplerian disk. While the data are consistent with a gas core that may rotate and/or collapse, we cannot exclude the outflow(s) and/or nearby expanding UCHII region as possible alternative causes of this velocity pattern.