Keywords:Sagittarius B2, CH3CN, molecular cloud, Hot Axis Effect
Traditionally used model of evolution of molecular clouds in interstellar space is described as increasing of cloud gas density from diffuse to dense conditions, i.e., from an atomic-gas cloud to a star-forming region via a diffuse cloud and a dense cloud. However, recently “reverse evolution” of molecular clouds is suggested by Price et al. . For example, outflow from a star-forming region makes a relatively-low-density cloud. To find a clue of reverse evolution, investigation of chemical composition of relatively-low-density clouds is necessary. Absorption of CH3CN can be observed by the hot axis effect, which shows special rotational distributions of CH3CN in a relatively-low-density cloud . In our previous work, CH3CN was detected via absorption of the J = 4–3 rotational transition in the envelope of Sagittarius B2(M) core in the Galactic Center region by using Nobeyama 45-m telescope . In this work, using ALMA data archive , we investigated absorption of the J = 5–4 and 6–5 rotational transitions of CH3CN in the envelope of Sagittarius B2(N) core, which is an adjacent core of the (M) core. The column density of CH3CN in the envelope of the (N) core is derived to be (1.0 ± 0.2) × 1015 cm−2, which is 7 times larger than that in the envelope of the (M) core, while the (N) core has an 11-times larger column density than the (M) core . Similar abundance relation was found in a case of HC3N. Thus, as chemical compositions of relatively-low-density clouds, it was found that an abundant core has an abundant envelope and vice versa.
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