G331.512–0.103: An Interstellar Laboratory for Molecular Synthesis. I. The Ortho-to-para Ratios for CH 3 OH and CH 3 CN

Abstract

Spectral line surveys reveal rich molecular reservoirs in G331.512–0.103, a compact radio source in the center of an energetic molecular outflow. In this first work, we analyze the physical conditions of the source by means of CH 3 OH and CH 3 CN. The observations were performed with the APEX Telescope. Six different system configurations were defined to cover most of the band within (292–356) GHz; as a consequence, we detected a forest of lines toward the central core. A total of 70 lines of A / E –CH 3 OH and A / E –CH 3 CN were analyzed, including torsionally excited transitions of CH 3 OH ( ). In a search for all the isotopologues, we identified transitions of 13 CH 3 OH. The physical conditions were derived considering collisional and radiative processes. We found common temperatures for each A and E symmetry of CH 3 OH and CH 3 CN; the derived column densities indicate an A / E equilibrated ratio for both tracers. The results reveal that CH 3 CN and CH 3 OH trace a hot and cold component with  K and  K, respectively. In agreement with previous ALMA observations, the models show that the emission region is compact ( ) with gas density n (H 2 ) = (0.7–1)×10 7  cm −3 . The CH 3 OH/CH 3 CN abundance ratio and the evidences for prebiotic and complex organic molecules suggest a rich and active chemistry toward G331.512–0.103.