用LOFAR探索恒星爆发矮不规则星系IC 10中星系风的形成
Exploring the making of a galactic wind in the star-bursting dwarf irregular galaxy IC 10 with LOFAR
摘要：
低质量星系受到强烈的星系外流的影响，其中宇宙射线可能起着重要的作用，它们可以最好地用低频射电连续观测来跟踪，这受光谱老化的影响较小。本文利用低频阵射线（LOFAR）在140 MHz、甚大阵（VLA）在1580 MHz、VLA和100 m Effelsberg望远镜在6200 MHz的观测资料，对附近的星暴矮不规则星系IC 10进行了研究。我们发现，IC 10有一个低频的无线电晕，这表现为第二个组件（厚盘）在短轴配置文件的非热无线电连续发射在140和1580 MHz。这些配置文件，然后拟合纯扩散和平流的一维宇宙射线传输模型。我们发现，扩散模型最适合，与扩散系数$D=(0.4$ - $0.8) \times 10^{26}(E/{\rm GeV})^{0.5}~{\rm cm^2\,s^{-1}}$，这是至少一个数量级小于从各向异性扩散和扩散长度的估计。与此相反，平流模型，不能排除由于温和的倾斜，而提供较差的拟合，导致平流速度接近$\approx$ $50~\rm km\,s^{-1}$的逃逸速度，如预期的宇宙射线驱动的风。我们喜欢的模型与加速风提供了一个自洽的解决方案，其中的磁场是在能量均分与温暖的中性和温暖的电离介质与宇宙射线的重要贡献。因此，宇宙射线可以在盘-晕界面的星系风发射中发挥至关重要的作用。
英文摘要：
Low-mass galaxies are subject to strong galactic outflows, in which cosmic rays may play an important role, they can be best traced with low-frequency radio continuum observations, which are less affected by spectral ageing. We present a study of the nearby star burst dwarf irregular galaxy IC 10 using observations at 140 MHz with the LOw-Frequency ARray (LOFAR), at 1580 MHz with the Very Large Array (VLA) and at 6200 MHz with the VLA and the 100-m Effelsberg telescope. We find that IC 10 has a low-frequency radio halo, which manifests itself as a second component (thick disc) in the minor axis profiles of the non-thermal radio continuum emission at 140 and 1580 MHz. These profiles are then fitted with 1D cosmic-ray transport models for pure diffusion and advection. We find that a diffusion model fits best, with a diffusion coefficient of $D=(0.4$-$0.8) \times 10^{26}(E/{\rm GeV})^{0.5}~{\rm cm^2\,s^{-1}}$, which is at least an order of magnitude smaller than estimates both from anisotropic diffusion and the diffusion length. In contrast, advection models, which cannot be ruled out due to the mild inclination, while providing poorer fits, result in advection speeds close to the escape velocity of $\approx$$50~\rm km\,s^{-1}$, as expected for a cosmic-ray driven wind. Our favoured model with an accelerating wind provides a self-consistent solution, where the magnetic field is in energy equipartition with both the warm neutral and warm ionized medium with an important contribution from cosmic rays. Consequently, cosmic rays can play a vital role for the launching of galactic winds in the disc--halo interface.
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