银河系中心分子区SiO比值的类抛物线趋势：银心过去核活动的可能特征
Parabolic-like Trend in SiO Ratios throughout the Central Molecular Zone: Possible Signature of a Past Nuclear Activity in the Galactic Center
AI总结：
本研究通过野边山45米望远镜观测发现银河系中心分子区SiO发射强度比呈类抛物线趋势，或为银心过去约10万年核活动爆发的特征，也可能与高能光子破坏小尘埃有关，为研究银心核活动历史提供新视角。
摘要：
我们报道了在银河系中心分子区（CMZ）内，SiO发射线强度比存在一种特征性趋势的发现。利用野边山射电天文台45米望远镜，我们对包括SiO $J$=2$-$1和CS $J$=2$-$1在内的分子谱线开展了大尺度、高灵敏度成图观测。通过识别发射SiO的分子云，并检验其与其他分子谱线的强度比，我们揭示出一种类抛物线趋势：在银心核区人马座A$^*$（Sgr A$^*$）附近比值较低，向CMZ边缘方向逐渐升高。该模式表明，银心核区在过去约$10^5$年内可能发生过一次爆发，其产生的强激波可能已传播至整个CMZ。此外，观测到的趋势也可能归因于高能光子对小尘埃颗粒的破坏。我们的研究结果有望为理解银心核活动历史及其对周围分子环境的影响提供新视角。
英文摘要：
We report the discovery of a characteristic trend in the intensity ratios of SiO emissions across the Central Molecular Zone (CMZ) of our Galaxy. Using the Nobeyama Radio Observatory 45-m telescope, we conducted large-scale, high-sensitivity imaging observations in molecular lines including SiO $J$=2$-$1 and CS $J$=2$-$1. By identifying SiO-emitting clouds and examining their intensity ratios relative to the other molecular lines, we unveiled a parabolic-like trend showing lower ratios near the Galactic nucleus, Sgr A$^*$, with gradual increases toward the edges of the CMZ. This pattern suggests a possible outburst of the nucleus within the last $\sim 10^5$ yr, which may have propagated through the entire CMZ with strong shocks. Alternatively, the observed trend may also be attributed to the destruction of small dust grains by high-energy photons. Our results can potentially lead to a new perspective on the history of nuclear activity and its impact on the surrounding molecular environment.
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