We explore what dominant physical mechanism sets the kinetic energy contained in neutral, atomic (HI) gas. We compare the HI line widths predicted from turbulence driven by supernova (SN) explosions and magneto-rotational instability (MRI) to direct observations in 11 disk galaxies. We use high-quality maps of the HI mass surface density and line width, obtained by the THINGS survey. We show that all sample galaxies exhibit a systematic radial decline in the HI line width, which appears to be a generic property of HI disks and also implies a radial decline in kinetic energy density of HI. At a galactocentric radius of r25 there is a characteristic value of the HI velocity dispersion of $10\pm2$ \kms. Inside this radius, galaxies show HI line widths above the thermal value expected from a warm HI component, implying that turbulence drivers must be responsible for maintaining this line width. Therefore, we compare maps of HI kinetic energy to maps of the star formation rate (SFR) and to predictions for energy generated by MRI. We find a positive correlation between kinetic energy of HI and SFR. For a given turbulence dissipation timescale we can estimate the energy input required to maintain the observed kinetic energy. The SN rate implied by the observed recent SFR is sufficient to maintain the observed velocity dispersion, if the SN feedback efficiency is at least ε_SN\simeq0.1. Beyond r25, this efficiency would have to increase to unrealistic values, $ε>1$, suggesting that mechanical energy from young stars does not supply most energy in outer disks. On the other hand, both thermal broadening and turbulence driven by MRI can produce the velocity dispersions and kinetic energies that we observe in this regime.
Gravitational contraction versus Supernova driving and the origin of the velocity dispersion-size relation in molecular clouds
分子云的观测表明，云有非热的速度色散，规模与云的大小为$σ\propto R^{1/2}$在恒定的表面密度，并为不同的表面密度规模与云的大小和表面密度，$σ^2 \propto R Σ$。驱动这些混沌运动的能量源仍然知之甚少。我们描述了在千秒差距尺度的磁化、超新星驱动、自引力、星际介质的数值模拟中形成的云群中观察到的速度色散，包括扩散加热和辐射冷却。我们比较速度色散，大小和表面密度之间的关系，在模拟的云人口中发现的银河系分子云的观测。我们发现，外部超新星爆炸不能驱动湍流运动的观测量级内的致密云。另一方面，在我们的模型中，当引力束缚的云开始坍塌时，自引力也会引起非热运动，通过这样做，它们的内部速度色散恢复了观测到的关系。能量守恒表明，观察到的行为与动能与引力能成正比是一致的。然而，我们模型中的云在任何时候都没有达到稳定平衡态的迹象，即使是强磁化的云。我们的结论是，引力束缚的分子云总是处于引力坍缩状态，它们的性质是这种混沌坍缩的自然结果。为了与观测到的恒星形成效率相一致，这个过程必须通过云的早期破坏而终止，可能是来自内部恒星反馈。
Are supernovae driving turbulence in the solar neighborhood?
Université Paris-Saclay（巴黎萨克雷大学）；Université Paris Cité（巴黎西岱大学）；CEA（法国原子能和替代能源委员会）；CNRS（法国国家科学研究中心）；University of Vienna（维也纳大学）；ENS de Lyon（里昂高等师范学校）；Universite Claude Bernard Lyon 1（里昂第一大学）；Universität Heidelberg（海德堡大学）；Laboratoire de Physique de l’Ecole Normale Supérieure（巴黎高等师范学院物理实验室）；ENS（巴黎高等师范学院）；Université PSL（巴黎文理研究大学）；Sorbonne Université（索邦大学）；Observatoire de Paris（巴黎天文台）；INAF - Istituto di Astrofisica e Planetologia Spaziali（意大利国家天体物理研究所）；Università di Roma Tor Vergata（罗马托尔维加塔大学）
School of Earth and Space Exploration, Arizona State University（亚利桑那州立大学地球与空间探索学院）；Hamburger Sternwarte, University of Hamburg（汉堡大学汉堡天文台）；Department of Astronomy, University of Maryland（马里兰大学天文学系）；X-ray Astrophysics Laboratory, NASA/GSFC（NASA/戈达德航天飞行中心X射线天体物理实验室）；Center for Research and Exploration in Space Science and Technology, NASA / GSFC (CRESST II)（NASA/戈达德航天飞行中心空间科学与技术研究探索中心）；NASA Goddard Space Flight Center（美国宇航局戈达德航天飞行中心）；Center for Astrophysics, Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；Department of Physics, Tokyo Metropolitan University（东京都立大学物理学系）
Role of prompt cusps in driving the core collapse of SIDM halos
Massachusetts Institute of Technology（麻省理工学院）；University of Chicago（芝加哥大学）；Carnegie Observatories（卡内基观测站）；Center for Astrophysics, Harvard & Smithsonian（哈佛-史密森天体物理中心）；Rice University（莱斯大学）
