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arXiv 0909.3854astro-ph.COastro-ph.GA
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Cosmic ray驱动的高红移星系外流

Cosmic ray driven outflows from high redshift galaxies

Saumyadip Samui, Kandaswamy Subramanian, Raghunathan Srianand

摘要:

我们研究高红移星系风驱动的相对论宇宙射线(质子)的组成部分,除了热的热气体成分。宇宙射线(CR)很可能在星系内部的超新星激波中有效地产生。我们得到的解决方案,这种CR驱动的自由风的引力势的NFW形式,有关星系。宇宙射线自然地为系统提供额外的能量和/或动量输入,这是绝热指数为$γ=5/3$的气体中的跨音速风解所需要的。我们表明,即使气体的热能由于辐射冷却而损失,CR也可以有效地驱动风。这些风的解决方案预测的渐近风速密切相关的圆周速度的星系。此外,对于质量为$M \sim 10^{11}-10^{12} M_\odot$的大质量星系,单位恒星形成率的质量流出率(eta_w)约为0.2-0.5。我们证明了eta_w与圆速度的平方成反比。磁场在$μ$ G水平也需要在这些星系有一个显着的质量损失。小质量星系的大eta_w意味着CR驱动的外流对矮星系的恒星形成有很强的负反馈作用。此外,我们的研究结果也将有重要的启示IGM的金属富集。这些结论适用于自由风模型中的源区域被限制在音速点。

英文摘要:

We study winds in high redshift galaxies driven by a relativistic cosmic ray (proton) component in addition to the hot thermal gas component. Cosmic rays (CRs) are likely to be efficiently generated in supernova shocks inside galaxies. We obtain solutions of such CR driven free winds in a gravitational potential of the NFW form, relevant to galaxies. Cosmic rays naturally provide the extra energy and/or momentum input to the system, needed for a transonic wind solution in a gas with adiabatic index $γ=5/3$. We show that CRs can effectively drive winds even when the thermal energy of the gas is lost due to radiative cooling. These wind solutions predict an asymptotic wind speed closely related to the circular velocity of the galaxy. Furthermore, the mass outflow rate per unit star formation rate (eta_w) is predicted to be ~ 0.2-0.5 for massive galaxies, with masses $M \sim 10^{11}-10^{12} M_\odot$. We show eta_w to be inversely proportional to the square of the circular velocity. Magnetic fields at the $μ$G levels are also required in these galaxies to have a significant mass loss. A large eta_w for small mass galaxies implies that CR driven outflows could provide a strong negative feedback to the star formation in dwarf galaxies. Further, our results will also have important implications to the metal enrichment of the IGM. These conclusions are applicable to the class of free wind models where the source region is confined to be within the sonic point.

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