Dust and gas emission in the prototypical hot core G29.96-0.02 at sub-arcsecond resolution

Abstract

Aiming at a better understand of the physical and chemical processes in the hot molecular core stage of high-mass star formation, we observed the prototypical hot core G29.96-0.02 in the 862mu band with the Submillimeter Array (SMA) at sub-arcsecond spatial resolution. The observations 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 1.4x0^5 protostars/pc^3. 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.