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arXiv 1707.09552astro-ph.HE
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活动星系核电离外流的密度诊断:类Be到类C离子亚稳能级的X射线和UV吸收线

Density diagnostics of ionized outflows in active galactic nuclei: X-ray and UV absorption lines from metastable levels in Be-like to C-like ions

Junjie Mao, J. S. Kaastra, M. Mehdipour, A. J. J. Raassen, Liyi Gu, J. M. Miller

摘要:

活动星系核(AGN)中的电离外流被认为会影响其核环境和局部星系环境。然而,外流相对于中央引擎的距离受到很大的限制,这限制了我们对它们作为宇宙反馈通道的动力学的理解。因此,活动星系核外流对其宿主星系的影响是不确定的。然而,当外流的密度是已知的,他们的距离可以立即从他们的建模电离参数。利用dac代码中新的自洽光电离(PION)模型,我们能够计算详细的能级粒子数,包括基态和亚稳态能级。这使我们能够确定在什么样的物理条件下,亚稳态水平显着填充。然后,我们从这些亚稳能级在1 - 2000 nm波长范围内确定特征线。在$n_H \in (10^6, 10^{20} m^{-3}$的大密度范围内,类铍离子中的亚稳能级2s 2 p $(^3P_{0-2})$可以被显著地占据.对于类B离子,只有第一激发能级2s $^2$ 2 p $(^2P_{3/2})$可以用作密度探针。对于类C离子,前两个激发能级2s $^2$ 2 p $^2$($^3P_1$和$^3P_2$)是比后两个激发能级2s $^2$ 2 p $^2$($^1S_0$和$^1D_2$)更好的密度探针。同一等电子序列中的不同离子不仅电离参数范围大,而且密度范围也大。另一方面,在相同的等离子体序列中,电离度较小的离子探测到的密度较低,电离参数较小。最后,我们重新分析了高分辨率的光栅光谱的NGC 5548观察钱德拉在2002年1月,使用一组的PION组件来解释电离流出。我们推导出较低(或较高)的等离子体密度在五个PION组件,基于亚稳态吸收线的存在(或不存在)。

英文摘要:

Ionized outflows in Active Galactic Nuclei (AGN) are thought to influence their nuclear and local galactic environment. However, the distance of the outflows with respect to the central engine is poorly constrained, which limits our understanding of their kinetic power as a cosmic feedback channel. Therefore, the impact of AGN outflows on their host galaxies is uncertain. However, when the density of the outflows is known, their distance can be immediately obtained from their modelled ionization parameter. With the new self-consistent PhotoIONization (PION) model in the SPEX code, we are able to calculate detailed level populations, including the ground and metastable levels. This enables us to determine under what physical conditions the metastable levels are significantly populated. We then identify characteristic lines from these metastable levels in the 1 -- 2000 Å wavelength range. In the large density range of $n_H \in (10^6, 10^{20} m^{-3}$, the metastable levels 2s 2p $(^3P_{0-2})$ in Be-like ions can be significantly populated. For B-like ions, merely the first excited level 2s$^2$ 2p $(^2P_{3/2})$ can be used as a density probe. For C-like ions, the first two excited levels 2s$^2$ 2p$^2$ ($^3P_1$ and $^3P_2$) are better density probes than the next two excited levels 2s$^2$ 2p$^2$ ($^1S_0$ and $^1D_2$). Different ions in the same isoelectronic sequence cover not only a wide range of ionization parameter, but also a wide range of density. On the other hand, within the same isonuclear sequence, less ionized ions probe lower density and smaller ionization parameter. Finally, we re-analyzed the high-resolution grating spectra of NGC 5548 observed with Chandra in January 2002, using a set of PION components to account for the ionized outflow. We derive lower (or upper) limits of plasma density in five out of six PION components, based on the presence (or absence) of the metastable absorption lines.

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