THE NEAR-INFRARED CORONAL LINE SPECTRUM OF 54 NEARBY ACTIVE GALACTIC NUCLEI-猫眼课题宝

DOI：

10.1088/0004-637x/743/2/100

发表时间：

2011-09

期刊：

The Astrophysical Journal

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

A. Rodr'iguez-Ardila;M. Prieto;J. G. Portilla;J. M. T. L. N. D. A. Mct;Brazil;Instituto de Astrof'isica de Canarias-Instituto-de-Astrof'isica-de-Canarias-102997450;Spain;Universidad Nacional de Colombia

首次基于近红外（0.8-2.4 μm）光谱分析了日冕线（CL）发射与 36 个 1 型和 18 个 2 型活动星系核（AGN）中核活动之间的关系。研究的 8 个 CL，包括 Si、S、Fe、Al 和 Ca 元素，对应于 125-450 eV 范围内的电离势 (IP)，在 67% (36 AGN) 的样品中检测到 (3σ)。我们的分析表明，四个最常见的 CL [Si vi] 1.963 μm、[S viii] 0.9913 μm、[S ix] 1.252 μm 和 [S x] 1.430 μm 显示出较窄的光度范围，大多数谱线位于 log L 39–40 erg s−1 区间。我们发现，无法探测到的现象在很大程度上与空间分辨率的损失或物距的增加有关：CL本质上是核的，很容易失去附近光源的连续恒星光的对比度，或者随着红移的增加而被强活动星系核连续谱稀释。然而，有些活动星系核可能确实缺乏日冕发射，即 IP ⩾ 100 eV 的谱线。这些谱线的缺失反映了非标准 AGN 电离连续谱，即缺乏几个 Kev 以下光子的非常硬的光谱。对谱线轮廓的分析指出了随着 IP 增加而增加 FWHM 的趋势，直至能量达到 300 eV 左右，此时 FWHM 达到最大值。对于更高的 IP 线路，FWHM 几乎保持不变或随着 IP 的增加而减小。当我们接近这些 AGN 的最内部区域时，我们将这种效应归因于密度环境的增加，其中密度高于 IP 大于 300 eV 的 CL 的临界密度。这为 108–109 cm−3 的窄区域和宽区域之间的边界区域的密度设定了严格的范围限制。观察到 CL 的光度与软、硬 X 射线发射和软 X 射线光子指数之间的关系：日冕发射随着 X 射线发射（软和硬）的增加和更陡的 X 射线光子指数（即更软的 X 射线光谱）而变得更强。因此，光电离似乎是主要的激发机制。仅考虑 1 类来源时，这些趋势成立；当包含 2 型源时，它们会变弱或消失，很可能是因为后者测量的 X 射线发射不是固有的电离连续谱。

The relationship between the emission of coronal lines (CLs) and nuclear activity in 36 Type 1 and 18 Type 2 active galactic nuclei (AGNs) is analyzed, for the first time, based on near-infrared (0.8–2.4 μm) spectra. The eight CLs studied, of Si, S, Fe, Al, and Ca elements and corresponding to ionization potentials (IPs) in the range 125–450 eV, are detected (3σ) in 67% (36 AGNs) of the sample. Our analysis shows that the four most frequent CLs [Si vi] 1.963 μm, [S viii] 0.9913 μm, [S ix] 1.252 μm, and [Si x] 1.430 μm display a narrow range in luminosity, with most lines located in the interval log L 39–40 erg s−1. We found that the non-detection is largely associated with either loss of spatial resolution or increasing object distance: CLs are essentially nuclear and easily lose contrast in the continuum stellar light for nearby sources or get diluted by the strong AGN continuum as the redshift increases. Yet, there are AGNs where the lack of coronal emission, i.e., lines with IP ⩾ 100 eV, may be genuine. The absence of these lines reflects a non-standard AGN ionizing continuum, namely, a very hard spectrum lacking photons below a few Kev. The analysis of the line profiles points out a trend of increasing FWHM with increasing IPs up to energies around 300 eV, where a maximum in the FWHM is reached. For higher IP lines, the FWHM remains nearly constant or decreases with increasing IPs. We ascribe this effect to an increasing density environment as we approach the innermost regions of these AGNs, where densities above the critical density of the CLs with IPs larger than 300 eV are reached. This sets a strict range limit for the density in the boundary region between the narrow and the broad region of 108–109 cm−3. A relationship between the luminosity of the CLs and that of the soft and hard X-ray emission and the soft X-ray photon index is observed: the coronal emission becomes stronger with both increasing X-ray emission (soft and hard) and steeper X-ray photon index, i.e., softer X-ray spectra. Thus, photoionization appears as the dominant excitation mechanism. These trends hold when considering Type 1 sources only; they get weaker or vanish when including Type 2 sources, very likely because the X-ray emission measured in the latter is not the intrinsic ionizing continuum.

THE NEAR-INFRARED CORONAL LINE SPECTRUM OF 54 NEARBY ACTIVE GALACTIC NUCLEI

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