太阳附近DIG的密度和填充因子
Densities and filling factors of the DIG in the Solar neighbourhood
摘要：
我们首次对38颗已知距离的云柱进行了色散测量和发射测量相结合，由此导出了云内平均电子密度N_c和沿视线平均的体积填充因子F_v。排放量的措施进行了修正，吸收尘埃和贡献以外的脉冲星的距离。结果如下：我们的样品中电子层的标度高度为0.93+/-0.13 kpc，中平面电子密度为0.023+/-0.004 cm^-3，与先前的结果一致。沿视线方向的平均密度为<n_e>= 0.018+/-0.002 cm^-3，几乎为常数。由于<n_e>= F_v N_c，F_v和N_c之间预期存在反比关系。我们发现F_v（N_c）=（0.011+/-0.003）N_c^{-1.20+/-0.13}，在N_c = 0.05-1 cm^-3和F_v = 0.4-0.01的范围内都成立。在银道面附近，F_v对N_c的依赖性明显强于远离银道面。F_v沿银道面或垂直于银道面不发生系统性变化，但在平均值0.08 ± 0.02附近的分布是相当大的。结论：F_v-N_c的逆关系与湍流引起的扩散电离气体（DIG）中的分级分形密度分布相一致。观察到的近恒常性<n_e>则是电离介质中分形结构的特征，这在薄圆盘之外最为明显。
英文摘要：
For the first time we have combined dispersion measures and emission measures towards 38 pulsars at KNOWN distances from which we derived the mean electron density in clouds, N_c, and their volume filling factor, F_v, averaged along the line of sight. The emission measures were corrected for absorption by dust and contributions from beyond the pulsar distance. Results: The scale height of the electron layer for our sample is 0.93+/-0.13 kpc and the midplane electron density is 0.023+/-0.004 cm^-3, in agreement with earlier results. The average density along the line of sight is <n_e> = 0.018+/-0.002 cm^-3 and nearly constant. Since <n_e> = F_v N_c, an inverse relationship between F_v and N_c is expected. We find F_v(N_c) = (0.011+/-0.003) N_c^{-1.20+/-0.13}, which holds for the ranges N_c = 0.05-1 cm^-3 and F_v = 0.4-0.01. Near the Galactic plane the dependence of F_v on N_c is significantly stronger than away from the plane. F_v does not systematically change along or perpendicular to the Galactic plane, but the spread about the mean value of 0.08+/-0.02 is considerable. Conclusions: The inverse F_v-N_c relation is consistent with a hierarchical, fractal density distribution in the diffuse ionized gas (DIG) caused by turbulence. The observed near constancy of <n_e> then is a signature of fractal structure in the ionized medium, which is most pronounced outside the thin disk.
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