G331.512-0.103: An interstellar laboratory for molecular synthesis. I. the ortho-to-para ratios for CH3OH and CH3CN

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 CH3OH and CH3CN. 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-CH3OH and A/E-CH3CN were analyzed, including torsionally excited transitions of CH3OH (nu(t) = 1). In a search for all the isotopologues, we identified transitions of (CH3OH)-C-13. The physical conditions were derived considering collisional and radiative processes. We found common temperatures for each A and E symmetry of CH3OH and CH3CN; the derived column densities indicate an A/E equilibrated ratio for both tracers. The results reveal that CH3CN and CH3OH trace a hot and cold component with T-k similar to 141. K and T-k similar to 74. K, respectively. In agreement with previous ALMA observations, the models show that the emission region is compact (<= 5 ''. 5) with gas density n(H-2) = (0.7-1)x10(7) cm(-3). The (CHOH)-O-3/(CHCN)-C-3 abundance ratio and the evidences for prebiotic and complex organic molecules suggest a rich and active chemistry toward G331.512-0.103.