星际介质中 MgS 和 NaS 的发现及 CaO 的初步探测
Discovery of MgS and NaS in the Interstellar Medium and tentative detection of CaO
AI总结：
本文首次在银河系中心分子云 G+0.693-0.027 中探测到含金属分子 NaS 和 MgS 并初步探测到 CaO，推导了其柱密度与丰度，探讨了含金属分子的星际化学形成路径，并基于含硫分子丰度高于含氧分子等现象指出该源中硫受低速冲击溅射而消耗较少。
摘要：
我们报告了在银河系中心分子云 G+0.693-0.027 方向的星际介质（ISM）中，首次探测到含金属分子硫化钠（NaS）和硫化镁（MgS），以及初步探测到一氧化钙（CaO）。推导出的柱密度分别为 (5.0±1.1) x 10^10 cm^-2、(6.0±0.6) x 10^10 cm^-2 和 (2.0±0.5) x 10^10 cm^-2。这转化为相对于 H2 的相对丰度分别为 (3.7±1.0) x 10^-13、(4.4±0.8) x 10^-13 和 (1.5±0.4) x 10^-13。我们还搜寻了该源方向的其他含 Na、Mg 和 Ca 的物种，但均未探测到，因此我们提供了其丰度的上限。我们讨论了在星际条件下形成这些含金属分子可能的化学路径。最后，我们比较了含金属与不含金属的含硫和含氧分子之间的比率，发现含金属硫分子比含金属氧分子丰富得多，这与不含金属的含氧和含硫分子比率中发现的一般趋势相反。这进一步强化了以下观点：由于该源中存在的低速冲击从尘埃颗粒中溅射出大量物质，G+0.693-0.027 中的硫可能消耗很少。
英文摘要：
We report the first detection of the metal-bearing molecules sodium sulfide (NaS) and magnesium sulfide (MgS) and the tentative detection of calcium monoxide (CaO) in the interstellar medium (ISM) towards the Galactic Center molecular cloud G+0.693-0.027. The derived column densities are (5.0+-1.1) x 10$^{10}$ cm$^{-2}$, (6.0+-0.6) x $^{10}$ cm$^{-2}$, and (2.0+-0.5) x $^{10}$ cm$^{-2}$, respectively. This translates into fractional abundances with respect to H$_2$ of (3.7+-1.0) x $10^{-13}$, (4.4+-0.8) x $10^{-13}$, and (1.5+-0.4) x $10^{-13}$, respectively. We have also searched for other Na-, Mg- and Ca-bearing species towards this source but none of them have been detected and thus we provide upper limits for their abundances. We discuss the possible chemical routes involved in the formation of these molecules containing metals under interstellar conditions. Finally, we compare the ratio between sulfur-bearing and oxygen-bearing molecules with and without metals, finding that metal-bearing sulfur molecules are much more abundant than metal-bearing oxygen ones, in contrast with the general trend found in the ratios between other non metal- oxygen- and sulfur-bearing molecules. This further strengthen the idea that sulfur may be little depleted in G+0.693-0.027 as a result of the low velocity shocks present in this source sputtering large amounts of material from dust grains.
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