An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. II. Spectroscopic classes and accretion modes in radio-loud AGN
An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. II. Spectroscopic classes and accretion modes in radio-loud AGN
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DOI：
10.1051/0004-6361/200913290
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发表时间：
2009-11
影响因子：
6.5
通讯作者：
S. Buttiglione;A. Capetti;A. Celotti;D. Axon;M. Chiaberge;F. Macchetto;William B. Sparks SISSA-ISAS
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文献类型：
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作者：
S. Buttiglione;A. Capetti;A. Celotti;D. Axon;M. Chiaberge;F. Macchetto;William B. Sparks SISSA-ISAS
在以前的论文中，我们提出了一个均匀的和92%完整的光谱数据集的3CR射电源的红移<0.3。在这里，我们使用发射线测量来探索样品的光谱特性。3CR源显示出双峰分布的激发指数，一种新的光谱指标，测量低和高激发线的相对强度。这揭示了存在两个主要的子群体的射电大声AGN，我们指的是，根据以前的研究，作为高和低激发星系（HEG和LEG，分别）。除了两个主要的类，我们发现一个源的光谱典型的星星形成星系，和3个对象的极低水平的激发。所有宽线天体都是HEG，从它们窄的发射线比率来看，所有HEG都是FR II射电星系，log L-178 [erg s（-1）]大于或接近32.8。相反，LEG覆盖了该3CR子样本所包含的整个无线电功率范围（30.7小于或类似于log L-178小于或类似于35.4），并且它们属于FR I和FR II类型。最亮的LEG都是FR II。HEG和LEG服从两个（准）线性之间的相关性的光学线和扩展的无线电光度，HEG比LEG在[O III]线由一个类似于10的因素。HEG和LEG也在一个比较黑洞质量和电离核光度的平面上偏移。然而，虽然HEG与较高的核光度，我们发现LEG之间的最明亮的无线电源的样本和一个明确的FR II形态，从HEG中看到的难以区分。这表明LEG不仅仅是具有较低吸积水平的物体。我们推测LEG和HEG之间的差异与不同的吸积模式有关：LEG由热气体提供动力，而HEG需要冷吸积材料的存在。LEG中的吸积气体的高温解释了缺乏“冷”结构（即分子环面和宽线区域），吸积盘的辐射输出减少，以及较低的气体激发。
In a previous paper we presented a homogeneous and 92% complete optical spectral dataset of the 3CR radio sources with redshift <0.3. Here we use the emission line measurements to explore the spectroscopic properties of the sample. The 3CR sources show a bimodal distribution of excitation index, a new spectroscopic indicator that measures the relative intensity of low and high excitation lines. This unveils the presence of two main sub-populations of radio-loud AGN to which we refer to, following previous studies, as high and low excitation galaxies (HEG and LEG, respectively). In addition to the two main classes, we find one source with a spectrum typical of star forming galaxies, and 3 objects of extremely low level of excitation. All broad-line objects are HEG from the point of view of their narrow emission line ratios and all HEG are FR II radio-galaxies with log L-178 [erg s(-1)] greater than or similar to 32.8. Conversely LEG cover the whole range of radio power encompassed by this 3CR subsample (30.7 less than or similar to log L-178 less than or similar to 35.4) and they are of both FR I and FR II type. The brightest LEG are all FR II. HEG and LEG obey to two (quasi) linear correlations between the optical line and extended radio luminosities, with HEG being brighter than LEG in the [O III] line by a factor of similar to 10. HEG and LEG are offset also in a plane that compares the black hole mass and the ionizing nuclear luminosity. However, although HEG are associated with higher nuclear luminosities, we find LEG among the brightest radio sources of the sample and with a clear FR II morphology, indistinguishable from those seen in HEG. This suggests that LEG are not simply objects with a lower level of accretion. We speculate that the differences between LEG and HEG are related to a different mode of accretion: LEG are powered by hot gas, while HEG require the presence of cold accreting material. The high temperature of the accreting gas in LEG accounts for the lack of "cold" structures (i.e. molecular torus and broad line region), for the reduced radiative output of the accretion disk, and for the lower gas excitation.