CHANG-ES XXXVII. 无线电尺度高度上光谱老化的影响
CHANG-ES XXXVII. Effects of spectral aging on radio scale heights
AI总结：
研究通过分析16个边缘星系的无线电数据，发现厚盘的尺度高度比与光谱指数相关，总质量影响光谱陡度，恒星形成率影响光谱平坦度，揭示了宇宙射线输运机制。
摘要：
背景。宇宙射线和磁场在星系的形成和演化中起着重要作用。无线电连续波观测使我们能够在边缘星系的晕中研究它们。目标。我们探索无线电尺度高度的频率依赖性，这取决于宇宙射线的输运和电子冷却。我们测试了基本星系属性，如恒星形成率（SFR）、质量和大小的影响。方法。我们使用了16个边缘星系的无线电连续波数据，这些数据来自“附近星系中的连续波晕——EVLA调查”（CHANG-ES）。我们包括了在144 MHz和3 GHz的低频阵列（LOw Frequency ARray）和Jansky大望远镜（Jansky Very Large Array）的观测数据，角分辨率为7角秒。我们提取了有效无线电半径内的垂直强度剖面，并拟合了受束宽卷积的双指数模型，以分离薄盘和厚盘。对于厚无线电盘，我们计算了144 MHz和3 GHz之间的平均光谱指数和尺度高度比。结果。我们发现平均尺度高度比为1.26±0.16。这比我们预期的要低，如果同步辐射和逆康普顿损失主导电子的行为，则宇宙射线扩散或对流的影响。比值与厚盘的光谱指数之间存在中等程度的正相关性：比值高的星系具有平坦的无线电光谱。比值不依赖于其他星系参数。厚盘的无线电光谱，如无线电光谱指数所示，随着总质量（强相关性）而变陡，随着恒星形成率-质量面密度（中等相关性）而变平。结论。具有银河风的星系在低频下具有平坦的无线电连续波光谱和较大的尺度高度。这表明在这些系统中宇宙射线的有效输运。
英文摘要：
Context. Cosmic rays and magnetic fields play an important role for the formation and evolution of galaxies. Radio continuum observations allows us to study them in the haloes of edge-on galaxies. Aims. We explore the frequency dependence of the radio scale height which depends on cosmic ray transport and electron cooling. We test the influence of fundamental galaxy properties, such as star-formation rate (SFR), mass and size. Methods. We used radio continuum data of 16 edge-on galaxies from the Continuum HAloes in Nearby Galaxies -- an EVLA Survey (CHANG-ES). We included maps from the LOw Frequency ARray at 144 MHz and from the Jansky Very Large Array at 3 GHz with 7" angular resolution. We extracted vertical intensity profiles within the effective radio radius and fitted beam-convolved double-exponential models to separate thin and thick discs. For the thick radio discs, we computed mean spectral indices and scale-height ratios between 144 MHz and 3 GHz. Results. We find a mean scale-height ratio of 1.26 \pm 0.16. This is much lower than what we would expect for either cosmic ray diffusion or advection if synchrotron and inverse Compton losses dominate for the electrons. There is a moderate positive correlation between the ratio and spectral index of the thick disc: galaxies with high ratios have flat radio spectra. The ratio does not depend on any other galaxy parameter. The radio spectrum of the thick disc, as indicated by the radio spectral index, steepens with total mass (strong correlation) and flattens with SFR-to-mass surface density (moderate correlation). Conclusions. Galaxies with galactic winds have flat radio continuum spectra and large scale heights at low frequencies. This shows effective transport of cosmic rays in such systems.
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