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arXiv 0908.0539astro-ph.GAastro-ph.HE
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Seyfert外流中的密度廓线

Density Profiles in Seyfert Outflows

Ehud Behar

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submitted to ApJ
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摘要：

在过去的十年中，电离流出的几个100公里/秒附近的塞弗特星系已被详细研究使用高分辨率X射线吸收光谱。这些流出物的反复出现的特征是它们的宽电离分布，基本上包括离子（例如，从中性到完全电离。吸收测度分布（AMD）定义为柱密度随电离参数的分布|d N_H/d（log xi）|.塞弗特外流的AMD可以跨越到xi的五个数量级。我们提出的AMD的五个流出，并表明，他们都是相当平坦的，也许稍微上升到高电离。更定量地说，对数AMD ~（log xi）^a的幂律拟合产生0 < a < 0.4的斜率。这些斜率严格限制了风的密度分布，到目前为止，这只能通过理论来解决。如果风分布在大尺度上，则测量的斜率意味着一般的密度径向廓线为n ~ r^{-alpha}，其中1 < alpha < 1.3。这种比例关系排除了质量守恒的n ~ r^{-2}径向流或等密度吸收体，但与非球形MHD流出模型一致，其中n ~ r^{-1}沿任何给定的视线。另一方面，如果电离变化是局部（delta r）密度梯度的结果，例如在湍流星际介质（ISM）中，AMD斜率意味着n ~ delta r^{-alpha}的密度标度，其中0.7 < alpha < 1.0，这与在银河系ISM中发现的、典型的不可压缩湍流的近似n ~ delta r^{0.4}的标度有很大的不同。

英文摘要：

For the past decade, ionized outflows of a few 100 km/s from nearby Seyfert galaxies have been studied in great detail using high resolution X-ray absorption spectra. A recurring feature of these outflows is their broad ionization distribution including essentially ions (e.g., of Fe) from neutral to fully ionized. The absorption measure distribution (AMD) is defined as the distribution of column density with ionization parameter |d N_H/d (log xi)|. AMDs of Seyfert outflows can span up to five orders of magnitude in xi. We present the AMD of five outflows and show that they are all rather flat, perhaps slightly rising towards high ionization. More quantitatively, a power-law fit for log AMD ~ (log xi)^a yields slopes of 0 < a < 0.4. These slopes tightly constrain the density profiles of the wind, which until now could be addressed only by theory. If the wind is distributed on large scales, the measured slopes imply a generic density radial profile of n ~ r^{-alpha} with 1 < alpha < 1.3. This scaling rules out a mass conserving radial flow of n ~ r^{-2}, or a constant density absorber, but is consistent with a non-spherical MHD outflow model in which n ~ r^{-1} along any given line of sight. On the other hand, if ionization variations are a result of local (delta r) density gradients, e.g. as in the turbulent interstellar medium (ISM), the AMD slopes imply density scaling of n ~ delta r^{-alpha} with 0.7 < alpha < 1.0, which is quite different from the scaling of approximately n ~ delta r^{0.4} found in the Milky Way ISM and typical of incompressible turbulence.

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