Extragalactic Sulfur Chemistry

摘要

As a result of the 2 mm line survey carried out towards the nucleus of the starburst galaxy NGC 253, a number of molecular species, not previously observed in the extragalactic ISM, have been detected. Among these new detections we found four sulfur-bearing molecules, namely SO2, H2S, H2CS and NS. Altogether with observations of the previously reported CS, SO and OCS molecules we are able to characterize the sulfur chemistry of this extragalactic nuclear region. When compared with selected prototypical Galactic sources, the observed emission appears to show similarities with the molecular cloud complexes within the central region of our Galaxy. Therefore, excitation by low velocity shocks is pointed out to be the leading mechanism that drives the molecular complexity observed. A brief comparison with chemical models is dicussed as well as the sulfur isotopic ratios derived through observations of the rare isotopic substitutions of CS, namely 13CS, C34S and C33S.