小合并产生的大撞击--NGC 4194美杜莎星系之眼中的异常热分子气流
Major impact from a minor merger - The extraordinary hot molecular gas flow in the Eye of the NGC 4194 Medusa galaxy
摘要：
小合并是重要的过程，对星系在宇宙年龄中的演化有重大贡献。它们对超大质量黑洞生长和恒星形成的影响是深远的。对星系中致密分子气体的详细研究，为检验不同星系尺度下恒星形成率与HCN光度关系的有效性提供了重要依据。我们使用HCN，HCO+1-0和CO 3 -2的观测研究密集气体的性质在美杜莎合并。我们计算的亮度温度比，并使用它们与非LTE辐射线传输模型。HCN和HCO+1-0和CO 3 -2排放不占据与低J CO排放相关的较低密度气体相同的结构。稠密气体的唯一排放是在“美杜莎之眼”内的200 pc区域内检测到的。没有HCN或HCO+检测到的扩展星爆。“眼睛”内部的CO 3 -2/2-1亮度温度比约为2.5 -迄今为止发现的最高比例。谱线比显示了“眼”内部极端的、碎片化的分子云群，温度很高（> 300 K），气体密度也很高（>10^4 cm^-3）。“眼睛”被发现在一个大规模的短轴流入和美杜莎中心区域之间的界面。“眼睛”内部的极端条件可能是一个深深嵌入的年轻大质量超级星团的辐射和机械反馈的结果，该星团是由于交叉点的气体堆积而形成的。或者，来自流入气体的冲击可能足够强以冲击和破碎气体。然而，对于这两种情况，HCN和HCO+致密气体示踪剂似乎不是在探测恒星的形成，而是在探测恒星暴和/或冲击后的ISM，因为太热和碎片化而无法形成新的恒星。因此，在将致密气体示踪剂的排放检测与正在进行或即将形成的恒星的证据联系起来时，应谨慎行事。
英文摘要：
Minor mergers are important processes contributing significantly to how galaxies evolve across the age of the Universe. Their impact on supermassive black hole growth and star formation is profound. The detailed study of dense molecular gas in galaxies provides an important test of the validity of the relation between star formation rate and HCN luminosity on different galactic scales. We use observations of HCN, HCO+1-0 and CO3-2 to study the dense gas properties in the Medusa merger. We calculate the brightness temperature ratios and use them in conjunction with a non-LTE radiative line transfer model. The HCN and HCO+1-0, and CO3-2 emission do not occupy the same structures as the less dense gas associated with the lower-J CO emission. The only emission from dense gas is detected in a 200pc region within the "Eye of the Medusa". No HCN or HCO+ is detected for the extended starburst. The CO3-2/2-1 brightness temperature ratio inside "the Eye" is ~2.5 - the highest ratio found so far. The line ratios reveal an extreme, fragmented molecular cloud population inside "the Eye" with large temperatures (>300K) and high gas densities (>10^4 cm^-3). "The Eye" is found at an interface between a large-scale minor axis inflow and the Medusa central region. The extreme conditions inside "the Eye" may be the result of the radiative and mechanical feedback from a deeply embedded, young, massive super star cluster, formed due to the gas pile-up at the intersection. Alternatively, shocks from the inflowing gas may be strong enough to shock and fragment the gas. For both scenarios, however, it appears that the HCN and HCO+ dense gas tracers are not probing star formation, but instead a post-starburst and/or shocked ISM that is too hot and fragmented to form new stars. Thus, caution is advised in linking the detection of emission from dense gas tracers to evidence of ongoing or imminent star formation.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
