KMS of Xinjiang Astronomical Observatory, CAS
| LLAGN射电性质与吸积盘光度相关性研究 | |
| Alternative Title | Correlation analysis of radio properties and accretion-disk luminosity for LLAGNs |
苏仁智
| |
| Subtype | 硕士 |
| Thesis Advisor | 刘祥 |
| 2017 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 天文技术与方法 |
| Keyword | 活动星系核 低光度活动星系核 射电喷流功率 射电噪度 吸积盘光度 相关性 |
| Abstract | 活动星系核（Active Galactic Nuclei，AGN）顾名思义是星系异常活耀的中心 区域。其核心很小的区域就能发出很高的光度，例如类星体光度可达1046erg/s至 1048erg/s。低光度活动星系核（Low Luminosity Active Galactic Nuclei，LLAGN）是相对于正常的或者说经典的AGN而言光度比较低的AGN，一般低几个数量级。一般把Hα线光度小于1040erg/s或者X-ray(2-10keV)的光度小于1042 erg/s的AGN称为LLAGN。LLAGN之所以光度低，一是因为LLAGN的中心黑洞质量相对较小，二是吸积率低，因而其吸积盘不是经典的标准薄盘而是ADAF盘。本论文主要对LLAGN的射电喷流功率、射电噪度和其吸积盘光度的 相关性等进行了研究。 本文的结构如下：第一章介绍了下AGN的背景知识；第二章介绍了LLAGN 的特点及前人对它的研究；第三章介绍了我们对LLAGN射电功率、射电噪度与吸积盘光度之间的相关性研究结果；并介绍了我在硕士期间参与的其它研究工作；第四章是研究工作总结及展望。 喷流的产生一般认为有两种方式，一种是黑洞的吸积产生喷流，另一种是黑洞的自旋产生喷流。以往的研究工作表明在经典的或者说比较亮的AGN中，黑洞吸积是产生喷流的主导方式。然而在LLAGN中，喷流的产生的物理可能不一样。所以为了弄清这个问题，我们对LLAGN做了统计研究。我们收集到了7个 LLAGN样本。这7个样本里的源大多数来自Palomar巡天，有一个自于斯隆巡天。这两个巡天提供了LLAGN的Hα光度LLAGN的射电流量密度来自于VLA和VLBI观测。另外X射线卫星提供了 LLAGN在X射线波段的辐射流量密度。有了 LLAGN光学发射线光度、射电流量密度以及X射线的流量密度，我们根 据一些经验方法得到了 LLAGN的吸积盘光度和射电功率，对于LLAGN的吸积盘光度，有Ldisk≈300LHα或Ldisk≈15.8Lx（2-10keV），对于喷流功率有pj=2.05×107（L1.4）6/7 （erg/s）。在得到LLAGN的吸积盘光度和射电功率后，我们对其做了相关性分析，采用的模型是pj"∝" L_disk^μ，得到LLAGN的射电功率和吸积盘光度的相关性幂律指数μ分布在0.4和0.7之间。这与亮的AGN的μ〜1不一样，说明在LLAGN中，黑洞的自旋对喷流的产生可能起了很重要的作用。 经过我们的推导，发现在黑洞自旋产生的喷流中，喷流功率和吸积盘的光度 的关系是Pspin〜a2m2(κ-1)L_disk^κ/ε，其中κ小于1。通过对7个LLAGN样本的射电功率和吸积盘光度的统计和拟合，如上所述我们得到的相关性幂律指数更倾向于喷流是黑洞自旋产生的，因为μ是明显小于1的，对自旋产生的喷流来说，μ即是κ。另外，黑洞自旋产生喷流的效率是ηspin"∝" a2rn2(K-1)，a是黑洞自旋参数，κ小于1，m是黑洞质量。对LLAGN，我们得到k在0.4和0.7之间，所以与黑洞质量呈负相关，若取k=0.5，那么ηspin正好与黑洞质量成反比，这意味着越低的黑洞质量，有越高的喷流效率。这就解释了为什么在统计上LLAGN中有比亮的AGN有更多射电噪的核。这些结果说明了黑洞自旋在LLAGN的喷流 产生中起主导的作用。 我们还对LLAGN的射电噪度与吸积盘光度做了相关性分析。在本文中，我们定义了两种射电噪度R=L1.4/Lx和R= L1.4/LHα。通过相关性分析发现这两种射电噪度R与吸积盘光度呈反相关关系，然而在经典的/亮的AGN中，我们知道射电噪度是和吸积盘光度是不相关或正相关的。之所以会这样，我们的模型是这样解释的，因为R"∝" L_disk^ρ，ρ=（7/6）μ-1，对于LLAGN，μ分布在0.4和0.7之间，所以有ρ< 0，即射电噪度与吸积盘光度负相关。在类星体和高光度的AGN 中，μ是大于等于1的，从而由上式得到它们的射电噪度和吸积盘光度基本上是不相关或正相关的。 |
| Other Abstract | Active Galactic Nucleus (AGN) is, as the name suggests, the center region of galaxy that is abnormally active. The compact region of AGN can radiate very high luminosity, for example, quasars often have luminosity of 1046〜1048erg/s. Relative to normal/typical AGN, Low-luminosity Active Galactic Nuclei (LLAGNs) are those of several orders of magnitudes less luminous than classical bright AGNs. LLAGNs are often defined as whose Ha line luminosity less than 1040 erg/s or X -ray (2-10 keV) luminosity less than 1042erg/s. The relatively low luminosity of LLAGN could be attributed to their lower black hole (BH) mass at the center of LLAGN and low accretion rate, so the accretion disk in LLAGN is not the typical thin disk but an ADAF disk. The aim of this research is to investigate the correlations among radio jet-power, radio loudness and accretion-disk luminosity of LLAGNs. The structure of this dissertation is: Chapter 1 introduces the background knowl¬edge of AGN; Chapter 2 introduces the properties and previous studies of LLAGNs; Chapter 3 introduces our research results among radio jet power, radio loudness and accretion disk luminosity of LLAGNs; here also introduces briefly other projects which the author has been involved; Chapter 4 is a summary and outlook. It is generally accepted that jet in AGN can be generated in two ways, one is the BH accretion the other is BH spin. It was showed in previous studies that BH accretion is the main mechanism in generating jet for quasars and luminous AGNs. However, the mechanism may be different for LLAGNs. In order to make clear for this problem, we carried out statistical studies for LLAGNs. We compiled 7 LLAGN samples. Almost all sources of first six samples are from Palomar survey while the last LLAGN sample is from Sloan Digital Sky Survey (SDSS). From the two surveys the Hα luminosity for the LLAGNs is available, and we collected the radio flux densities of LLAGNs from VLA or VLBI observations. In addition, the X-ray band fluxs for the LLAGNs are obtained from X-ray astronomical satellites. With the optical line luminosity, radio flux density and X-ray flux of LLAGNs, we calculated their accretion disk luminosity and radio power by empirical methods, for the accretion disk luminosity Ldisk≈300LHα或Ldisk≈15.8Lx（2-10keV）, for the jet power pj=2.05×107（L1.4）6/7 （erg/s）, and then we carried out a correlation analysis between them with the model pj"∝" L_disk^μ. The results show that the power-law correlation index μ between radio power and accretion disk luminosity of LLAGN ranges from 0.4 to 0.7 for the 7 LLAGN samples. Which is different from luminous AGN that is μ〜1，this argues that BH spin may paly a significant role in generating jet of LLAGNs. From our analysis, it is found that the radio power and accretion disk luminosity has the relation Pspin〜a2m2(κ-1)L_disk^κ/ε (κ<1) in the situation of BH spin generated jet. Based on the statistical and fitting results of 7 LLAGN samples, the power-law correlation index that we obtained prefers to the jet generated by BH spin in LLAGNs, because μ is significantly less than unity, here for the BH spin generated jet, actually μ is k. Furthermore, for the jet generated from BH spin, its efficiency is ηspin"∝" a2m2(K-1) where a is the parameter of BH spin, k<1 and m is the BH mass. For LLAGNs, we have k ranges from 0.4 to 0.7, so ηspin is anti-correlated with BH mass, and if k=0.5, then ηspin is just inversely proportional to BH mass, which means lower the BH mass higher the jet efficiency. This explained, in statistics, that why LLAGNs have more radio-loud nucleus than luminous AGNs. These results argue that BH spin play a dominant role in generating jet of LLAGNs. We also analyzed the correlation between radio loudness and accretion disk luminosity for LLAGNs. In this dissertation, we define two kinds of radio loudness which are R=L1.4/LX and R=L1.4/LHα. From the correlation analysis, it is showed that these two kinds of radio lundness are all anti-correlated with accretion disk luminosity. Whereas, we knew that there is no correlation or positive correlation between radio loudness and accretion disk luminosity in luminous AGNs. This difference can be explained with our model R"∝" L_disk^ρ,ρ=（7/6）μ-1, for LLAGNs, μ~0.4-0.7, so ρ < 0 which indicates an anti-correlation between radio loudness and accretion disk luminosity of LLAGNs. Whereas for quasars and luminours AGN, the μ≥1, so that leads to the nearly no correlation or positive correlation between the radio loudness and the accretion disk luminosity. |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/1707 |
| Collection | 研究生学位论文 射电天文研究室 |
| Affiliation | 中国科学院新疆天文台 |
| Recommended Citation GB/T 7714 | 苏仁智. LLAGN射电性质与吸积盘光度相关性研究[D]. 北京. 中国科学院大学,2017. |
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| 2017届硕士学位论文-苏仁智.pdf（3638KB） | 暂不开放 | CC BY-NC-SA | Application Full Text | |||
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