Kinematics and chemistry of the hot molecular core in G34.26+0.15 at high resolution

We present high angular resolution (similar to 1 '') multitracer spectral line observations toward the hot molecular core (HMC) associated with G34.26+0.15 between 87 and 109 GHz. We have mapped emission from(1) complex nitrogen- and oxygen-rich molecules such as CH3OH, HC3N, CH3CH2CN, NH2CHO, CH3OCH3, and HCOOCH3; (2) sulfur-bearing molecules such as OCS, SO, and SO2; and (3) the recombination line H53 beta. At this high resolution (0.018 pc) we find no evidence for the HMC being internally heated. The continuum peak detected at lambda = 2.8 mm is consistent with the free-free emission from component C of the ultracompact H ii region, which primarily energizes the HMC. Emissions from the N- and O-bearing molecules peak at different positions within the core; none is coincident with the continuum peak. Lack of high-resolution complementary data sets makes it difficult to decipher whether the different peaks correspond to separate hot cores not resolved by the present data, or whether they are manifestations of the temperature and density structure within a single core. Using brightness temperatures of the optically thick lines in our sample, we estimate the kinetic temperature of the inner regions of the HMC to be 160 +/- 30 K. Observed abundances of the different chemical species are not consistently reproduced by the existing hot-core models. There are uncertainties due to (1) unavailability of temperature and density distribution within the hot core, (2) the assumption of a centrally peaked temperature distribution by the chemical models, which is not applicable to externally heated hot cores such as G34.26+0.15, and (3) inadequate knowledge about the formation mechanism of many of the complex molecules.