A study of three southern high-mass star-forming regions

摘要

Context. Based on color-selected IRAS point sources, we have started to conduct a survey of 47 high-mass star-forming regions in the southern hemisphere in 870 μm dust continuum and molecular line emission in several frequency ranges between 290 GHz and 806 GHz. This paper describes the pilot study of the three sources IRAS 12326-6245, IRAS 16060-5146, and IRAS 16065-5158. Aims. To characterize the physical and chemical properties of southern massive star-forming regions, three high-luminosity southern hemisphere hot cores are observed in continuum and molecular line emission. Based on the results obtained in the three sources, which served as templates for the survey, the most promising (and feasible) frequency setups for the remaining 44 sources were decided upon. Methods. The sources were observed with the Atacama Pathfinder EXperiment (APEX) in five frequency setups aimed at groups of lines from the following molecules: CH_3OH, H_2CO, and CH_3CN. Using the LTE approximation, temperatures, source sizes, and column densities were determined through modeling of synthetic spectra with the XCLASS program. Dust continuum observations were done with the Large APEX BOlometer CAmera (LABOCA) at 870 μm and the 3 mm continuum was imaged with the Australia Telescope Compact Array (ATCA). Results. Based on the detection of high-excitation CH_3CN lines and lines from complex organic species, the three sources are classified as line rich, hot core type sources. For all three, the modeling indicates that the line emission emerges from a combination of an extended, cooler envelope, and a hot compact component. All three sources show an overabundance of oxygen-bearing species compared to nitrogen-bearing species. While the chemistry in the three sources indicates that they are already in an evolved stage, the non-detection of infrared heating sources at the dust continuum peak of IRAS 16065-5158 points to this source still being deeply embedded. Because this work served as a pilot study, the approach to observe the remaining 44 massive star-forming regions was chosen based on its results. Conclusions. The three sources are massive, luminous hot cores. While IRAS 16065-5158 seems to be a very young deeply embedded object, IRAS 12326-6245 and IRAS 16060-5146 seem more evolved and have already developed UCHii regions.