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arXiv 0804.0218astro-ph
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对矮塞弗特1星系NGC 4395的多波长监测。IV。变UV吸收线

Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. IV. The Variable UV Absorption Lines

Alexei Baskin, Ari Laor

备注：
Accepted for publication in The Astrophysical Journal
发表信息：
Astrophys.J. 682 (2008) 110-126
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摘要：

我们报告的可变紫外吸收线在NGC 4395的检测，紫外线观测的基础上与HST STIS在2004年4月和7月进行的，作为混响映射活动的一部分。O I、N I、Si II、C II和Fe II的低电离线出现在低态光谱（2004年4月）中，速度为v_shift=-250 km/s（系统A_l），另外C IV和N V的高电离线出现在高态光谱（2004年7月）中，速度为v_shift=-250 km/s（系统A_h）和v_shift=-840 km/s（系统B）。没有来自Si II的低亚稳能级的吸收意味着系统A_1的密度<~10^3 cm^（-3），表明其位于窄线区（NLR）之外。A_h体系是一个特殊的体系，只有N V吸收被清楚地检测到.预计高的N V/C IV吸收比的高金属量的吸收剂，但这是排除在这里的主星系和核气体的金属量是显着subsolar。对于系统A_h和B，一个简单的可接受的模型是位于宽线区（BLR）和NLR之间的吸收体，它只吸收连续谱和BLR。在低态下，C IV和N V的强窄发射线主导光谱，使得吸收不可见。在高态下，吸收的连续谱和BLR发射占主导地位。因此，所观察到的吸收的变化并不反映吸收体的变化，而是来自吸收体后面的连续谱和BLR发射相对于来自吸收体前面的NLR的发射的变化。因此，对高度可变物体的吸收线可变性的研究可以打破单历元研究所固有的吸收体距离确定中的简并性。

英文摘要：

We report the detection of variable UV absorption lines in NGC 4395, based on UV observations with the HST STIS carried out in April and July, 2004, as part of a reverberation-mapping campaign. Low-ionization lines of O I, N I, Si II, C II, and Fe II, are present in the low-state spectra (April 2004) at a velocity v_shift=-250 km/s (system A_l), and additional high-ionization lines of C IV and N V appear in the high-state spectra (July 2004) at v_shift=-250 km/s (system A_h) and at v_shift=-840 km/s (system B). The absence of absorption from the low metastable levels of Si II implies a density <~10^3 cm^(-3) for system A_l, indicating a location outside the narrow line region (NLR). System A_h is peculiar as only N V absorption is clearly detected. A high N V/C IV absorption ratio is expected for a high metallicity absorber, but this is excluded here as the metallicity of the host galaxy and of the nuclear gas is significantly subsolar. A simple acceptable model for systems A_h and B is an absorber located between the broad line region (BLR) and the NLR, which absorbs only the continuum and the BLR. At the low-state the strong narrow emission lines of C IV and N V dominate the spectrum, making the absorption invisible. At the high-state the absorbed continuum and BLR emission dominate the spectrum. Thus, the change in the observed absorption does not reflect a change in the absorber, but rather a change in the continuum and BLR emission from behind the absorber, relative to the emission from the NLR in front of the absorber. Studies of the absorption line variability in highly variable objects can thus break the degeneracy in the absorber distance determination inherent to single epoch studies.

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