M51中星际介质的动力学驱动演化
Dynamically Driven Evolution of the Interstellar Medium in M51
摘要：
本文报道了对旋涡星系M51的高精度CO辐射观测，揭示了巨分子云（GMC）相对于大尺度星系结构和动力学的演化。最大质量的GMC（所谓的GMA）首先组装，然后随着气体流过螺旋臂而分解。GMAs和它们的H2分子并没有像在恒星反馈情景中预测的那样完全解离成原子气体，而是在离开旋臂时分裂成更小的GMCs。残留的GMAs被检测为从旋臂进入臂间区域的GMCs链。螺旋臂内的运动剪切足以使GMA克服自重而脱离。我们的结论是，GMCs的演变是由大规模的星系动力学-他们的凝结成GMAs是由于螺旋臂流运动后进入武器，其次是由于剪切碎片，因为他们离开下游侧的武器。在M51中，大部分气体从臂进入通过臂间区域并进入下一个螺旋臂通道时保持分子状态。
英文摘要：
We report the highest-fidelity observations of the spiral galaxy M51 in CO emission, revealing the evolution of giant molecular clouds (GMCs) vis-a-vis the large-scale galactic structure and dynamics. The most massive GMCs (so-called GMAs) are first assembled and then broken up as the gas flow through the spiral arms. The GMAs and their H2 molecules are not fully dissociated into atomic gas as predicted in stellar feedback scenarios, but are fragmented into smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as the chains of GMCs that emerge from the spiral arms into interarm regions. The kinematic shear within the spiral arms is sufficient to unbind the GMAs against self-gravity. We conclude that the evolution of GMCs is driven by large-scale galactic dynamics --their coagulation into GMAs is due to spiral arm streaming motions upon entering the arms, followed by fragmentation due to shear as they leave the arms on the downstream side. In M51, the majority of the gas remains molecular from arm entry through the inter-arm region and into the next spiral arm passage.
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