Modelling the cosmic ray electron propagation in M 51
Modelling the cosmic ray electron propagation in M 51
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模拟 M 51 中的宇宙射线电子传播
DOI：
10.1051/0004-6361/201628446
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Fletcher
中科院分区：
文献类型：
--
作者：
Mulcahy;Fletcher
宇宙射线电子（cre）是星际介质的重要组成部分，是通过同步加速器发射观测到的。虽然对银河系的CRE分布和传播进行了大量的建模，但对正常的外部恒星形成星系的建模却很少。来自新一代射电望远镜的最新光谱数据使我们能够对CRE的传播进行更可靠的估计。目的利用扩散能量损失方程对m51的同步加速器光谱指数进行建模，并将模型结果与LOFAR最近低频观测所得的光谱指数进行比较。方法求解m51中CREs随时间的扩散能量损失方程。这是CRE传播模型第一次解决了CRE源的实际分布，我们从观测到的恒星形成率中得到CRE源。将模型产生的同步加速器光谱指数和尺度长度的径向变化与最近的LOFAR和VLA观测数据以及GMRT在325 MHz获得的m51新观测数据进行了比较。结果cre仅通过扩散传播就足以再现m51中观测到的光谱指数分布。发现各向同性扩散系数为6.6±0.2 × 1028cm2s-1的值最适合，并且与在银河系中看到的相似。我们估计从中央星系到扩展盘的逃逸时间为11myr至88myr。在0.01 GeV - 3 GeV范围内，扩散系数的能量依赖性不显著。我们能够重现观测到的同步加速器标度长度与频率的关系，在外盘中∝ν−1 / 4，在内盘中∝ν−1 / 8。
ContextCosmic ray electrons (CREs) are a crucial part of the interstellar medium and are observed via synchrotron emission. While much modelling has been carried out on the CRE distribution and propagation of the Milky Way, little has been done on normal external star-forming galaxies. Recent spectral data from a new generation of radio telescopes enable us to find more robust estimations of the CRE propagation.AimsTo model the synchrotron spectral index of M 51 using the diffusion energy-loss equation and to compare the model results with the observed spectral index determined from recent low-frequency observations with LOFAR.MethodsWe solve the time-dependent diffusion energy-loss equation for CREs in M 51. This is the first time that this model for CRE propagation has been solved for a realistic distribution of CRE sources, which we derive from the observed star formation rate, in an external galaxy. The radial variation of the synchrotron spectral index and scale-length produced by the model are compared to recent LOFAR and older VLA observational data and also to new observations of M 51 at 325 MHz obtained with the GMRT.ResultsWe find that propagation of CREs by diffusion alone is sufficient to reproduce the observed spectral index distribution in M 51. An isotropic diffusion coefficient with a value of 6.6 ± 0.2 × 1028cm2s-1is found to fit best and is similar to what is seen in the Milky Way. We estimate an escape time of 11 Myr from the central galaxy to 88 Myr in the extended disk. It is found that an energy dependence of the diffusion coefficient is not important for CRE energies in the range 0.01 GeV–3 GeV. We are able to reproduce the dependence of the observed synchrotron scale-lengths on frequency, withl∝ν− 1 / 4in the outer disk andl∝ν− 1 / 8in the inner disk.
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发表时间：
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DOI：
10.1088/0004-637x/764/1/37
发表时间：
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期刊：
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影响因子：
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