中国科学院机构知识库网格
Chinese Academy of Sciences Institutional Repositories Grid
高红移星际尘埃与活动星系核中心黑洞质量

文献类型:学位论文

作者王建国
学位类别博士
答辩日期2011-12-02
授予单位中国科学院研究生院(云南天文台)
授予地点北京
导师袁为民
关键词星际介质 尘埃 消光 类星体吸收线系统 黑洞物理
其他题名Interstellar dust at high redshifts and the black hole masses of active galactic nuclei
学位专业天体物理
中文摘要类星体(QSO或quasar)是宇宙中最亮的天体之一,是少数在高红移还能进行谱观测的天体。来自遥远宇宙的类星体的光谱中包含了大量的信息,这些光谱不仅携带着类星体本身及寄主星系的信息,同时也包括在它向我们传播的过程中所经历的星际介质及星系际介质的信息。类星体给我们提供了研究星系形成和演化以及类星体本身的能源机制的机会。本文主要介绍我们基于活动星系核光学及紫外波段的光谱分析开展的高红移星际尘埃与活动星系核中心黑洞质量的研究。 论文第一部分主要介绍了高红移星际尘埃的研究。基于类星体本征谱指数分布,我们构建了一个类星体本征光谱库。用多个模板的统计结果来寻找类银河系消光曲线并估计其不确定性。 第二章主要介绍了模板库的构建过程及用模板库估计消光曲线的方法,并应用于一个富尘埃富金属的阻尼莱曼alpha吸收系统(Damped \lya~Absorption system,简称DLAs\footnote{在本文中,若无特别说明就指在类星体中发现的DLA。 })。 我们首先测量DLA的消光曲线,发现了一个显著的2175\AA\ 尘埃吸收特征。这个DLA对类星体的消光达到$A_V \approx 0.92$星等,如此的消光在类星体DLA中从未发现过。用我们测量的消光曲线褪红化之后,我们发现这个类星体本征光度其实很高,是当前类星体样本中最亮的之一。我们用MMT BCS的光谱测量了DLA中的中性氢、\znii、 \feii、\cii、\alii\和\siii\ 等元素的吸收柱密度。我们发现其中性氢吸收柱密度 ($N_{\rm \hi} = 10^{21.8\pm0.2}$~cm$^{-2}$)是DLA中最高的之一。其\znii\柱密度($N_{\rm ZnII}\approx 10^{13.8}$~cm$^{-2}$)是已知DLA中最高的, 是之前最高记录的2.5倍。由于吸收线非常宽,金属吸收线柱密度可能只是下限。这个DLA中非常大的尘埃耗散[Zn/Fe]$\approx1.1$表明这个DLA中的大量金属沉积到尘埃中。其尘埃耗散模式介于银河系内的冷暖星云之间。如此高柱密度高金属丰度的DLA很少,在金属丰度-$N_{\rm \hi}$平面上架起了DLA与在伽玛暴余辉中发现的DLA(GRB-DLA)之间的桥梁。这样的DLA有利于 认识产生两类DLA不同观测性质的原因。高柱密度高金属丰度往往会导致严重消光,我们发现高金属柱密度的DLA倾向于在暗的类星体的光谱中发现。这类DLA可能会对目前测量的中性氢密度和金属丰度的宇宙学演化有重要影响。 第三章我们介绍2175\AA\ 尘埃吸收样本及类星体本征2175\AA\ 尘埃吸收的研究。我们在 Sloan Digital Sky Survey data release 7 (简称SDSS DR7)的光谱数据中发现了42个有2175\AA\ 尘埃吸收的候选体。这个样本的初步测量结果表明这些2175\AA\ 吸收特征的中心位置以及宽度分布比银河系内的分布范围更宽,强度更弱。这可能是由于不同的环境造成的,也可能我们比较大的测量误差造成的,或两者兼有。有些候选体的2175\AA\ 吸收特征强度比较大,但是光学波段消光却几乎是零。这表明这些候选体中的尘埃的大小分布非常奇怪,大尘埃远远少于小尘埃甚至完全消失。这种特殊的尘埃大小分布很可能是由于正常开恶劣的环境破坏了大尘埃而形成的。我们着重分析了一个有本征2175\AA\ 尘埃吸收特征的类星体 SDSS SDSS J091613.60+$292106.1(简称J0916$+$2921)。其2175\AA\ 尘埃吸收特征非常明显,探测置信度有$6\sigma$ 。MMT BCS的光谱分析表明它的尘埃耗散很大[Zn/Fe]$\approx1.01$。然而,XMM-Newton的X-射线谱拟合却没有探测到显著的吸收气体,这说明这个源内的尘气比非常高。强X辐射场的存在也限定最小的尘埃不能小于10\AA \ucite{1991ApJ...379..122V}。这类源可能会对尘埃化学组成提出强的限制。 论文第二部分主要介绍了活动星系核中心黑洞质量的研究。目前,大样本的活动星系核中心黑洞质量估计都是使用一些基于活动星系核反响映射(Reverberationmapping,简称RM)的结果而得到的经验的维里关系。用Peterson等人(2004)总结的35个活动星系核反响映射的\hb\ 数据\ucite{2004ApJ...613..682P}及部分源的更新和我们测量的其中29个活动星系核的\mgii\ 半高全宽,我们证实\hb\ 和\mgii\ 半高全宽都不能很好的代替维里速度。它们与当前最好的维里速度的指示 ---方均根谱中的\hb\ 的$\sigma_{\rm line}$---的关系是非线性的。这表明直接用\hb\ 和\mgii\ 的 半高全宽代替维里速度而得到的黑洞质量与真实的黑洞质量之间存在系统性偏差。我们首次尝试自由拟合半高全宽的指数而重新定标了基于单周期谱的\hb\和\mgii\ 半高全宽的黑洞质量公式。与以前的公式相比,我们的公式得到的黑洞质量统计上更接近反响映射得到的黑洞质量,并且弥散也小。我们用SDSS的大样本检验我们的两个公式,发现它们得到的黑洞质量很一致。以前的公式得到的黑洞质量大多都和我们的公式得到的黑洞质量存在系统性偏差。这种系统性偏差会导致很多假的相关性,如:用\hb\ 和\mgii\ 估计的黑洞质量的偏差与吸积率的相关\ucite 08ApJ...689L..13O},而用我们的公式时,这个相关消失。
英文摘要Quasars, also quasi-stellar objects (QSOs), are luminous active galactic nuclei (AGNs) and the brightest steady objects in the universe. They can be observed spectroscopically up to high redshifts.The spectra of quasars from the distant universe carry a lot of information about quasars themselves, their host galaxies, the interstellar media (ISM) and the intergalactic media (IGM) on their way to us. Quasars provide us with the opportunities to study the formation and evolution of galaxies and the physical mechanisms of the central engine of AGNs. The aims of this thesis is twofold: one is to study dust in the ISM at high redshifts and the other is to study the black hole masses of AGNs by analyzing optical and ultraviolet spectra. The first part of the thesis is on the interstellar dust at high redshifts. In order to search for the Milky Way(MW)-type extinction curves and to model their uncertaintities, we build up a libray of intrinsic spectra of quasars according to the distribution of their power-law spectral indices. We refer to this method as “quasar spectra pair method”. In chapter 2, details of the building up of the libray and the scheme for modelling the extinction curve are given. The quasar spectra pair method is used to determine the extinction curve of a metal-strong and dust-rich Damped \lya~Absorption system (DLAs \footnote{In this thesis, this abbreviation is referred to as quasar DLAs unless further specified. }). The derived extinction curve is MW-type with a significant broad 2175 \AA\ dust absorption feature. The derived extinction is very high with $A_V \approx 0.92$ mag, which is unprecedented in quasar DLAs. We measure the column densities of \hi\ ,~\znii\ ,~\feii\ ,~\cii\ ,~\alii~and \siii~from spectra taken with the Multiple Mirror Telescope (MMT). The neutral hydrogen column density, $\rm N_{\hi} = 10^{21.8\pm0.2}$~cm$^{-2}$,is among the highest values reported in quasar DLAs. The measured \znii~column density is $\rm N_{ZnII}\approx 10^{13.8}$~cm$^{-2}$, which is about 1.5 times larger than e highest value in reported quasar DLAs. The column densities of metal absorption lines may be lower limits because these absorption lines are very broad. The large relative gas-phase chemical abundance of [Zn/Fe]$\approx1.0$ indicates that metals are heavily depleted onto dust grains and the dust depletion level is between that of the warm and the cool clouds toward $\zeta$~Oph in the MW. DLAs with high metallcity and high $\rm N_{\hi}$ are rare and they bridge the gap between quasar DLAs and DLAs in the spectra of Gamma-ray burst (GRB) afterglows (GRB-DLAs) on the metallicity-$N_{\hi}$ plane. They are helpful to understand the differences between DLAs and GRB-DLAs. High extinction is usually related to high $\rm N_{\hi}$ and/or high metallicity. DLAs with high metal column densities tend to be found in dim quasars according to the correlation between N$_{\rm \znii}$ of metal-strong DLAs and r magnitude. Metal-strong and dust-rich DLAs could have significant influences on the cosmic evolution of the \hi\ density and metallicity. In chapter 3, we build up a sample of quasars showing the 2175 \AA\ absorption bump in their spectra from the SDSS and study the 2175 \AA\ feature associated with quasars. A preliminary statistical investigation of the sample indicate that the distribution of the centers and widths of these 2175\AA\ bumps are broader than that in the MW while the bump strengths are weaker than that in the MW. These differences may be caused by different environment of the dust as well as large uncertaintities in the measurements. Meanwhile, the bump strengths of some candidates are very large while there is almost no extinction in the optical band. This indicates the distributions of dust size in these candidates are very peculiar. The number of large-sized dust particles may be much smaller than that of small-sized ones. These peculiar size distributions of the dust are likely caused by violent events, such as AGNs activities, because the large-sized dust particles are easy to destroy by sputtering. We then focus on the detection of a 2175\AA\ bump associated with quasar SDSS SDSS J091613.60$+$292106.1 (hereafter J0916$+$2921). The 2175\AA\ bump in the object is detected at the $6\sigma$ confidence level. An analysis of a spectrum taken with BCS on MMT indicates that the dust depletion is large with [Zn/Fe]$\approx1.01$. However, its X-ray spectrum observed with XMM-Newton does not show significant evidence of X-ray absorption. This indicates that the dust-to-gas ratio of the quasar is very high. Meanwhile, the minimum size of the dust was constrained to be 10\AA\ as smaller dust would have been destructed by the strong X-ray radiation field\ucite{1991ApJ...379..122V}. The object could provide strong constraints on the composition of the dust. The second part of the thesis is on the black hole mass (\mbh) of AGNs. Currently estimation of \mbh\ of AGNs has been made possible by using an empirical virial formalism, which is calibrated with the result of reverberation mapping (RM). Using the \hb\ data of 35 AGNs presented by Peterson et al. (2004) \ucite{2004ApJ...613..682P} along with recent updates and our new measurements of \mgii\ FWHM of 29 out of these AGNs, we found neither the \hb\ FWHM nor the \mgii\ FWHM is a good tracer of Virial velocity. The relations between the FWHM of either \hb\ or \mgii\ and the $\sigma_{\rm line}$ of \hb\ measured from the root-mean-square (RMS) spectra, which is considered as the best indicator of Virial velocity of the broad line region, is nonlinear. We re-calibrate the \mbh\ formalisms by setting the power index on FWHM to be a free parameter and determining it from fitting the formalisms to the data and \mbh\ obtained from RM. Our formalisms improve over the previous ones by giving \mbh\ much more consistent with the RM-based \mbh , as well as smaller scatter. Moreover, the two formalisms, one based on \hb\ and the other based on \mgii , give self-consistent \mbh\ estimation, when applying them to a large AGN sample from the SDSS. The systematic bias in previous \mbh\ estimation formalisms, as we find in this work, would inevitably lead to some artificial correlations, as reported in the literature. For example, the difference between \hb-based \mbh\ and \mgii-based \mbh\ is systematically correlated with the Eddington ratio\ucite{2008ApJ...689L..13O}; however, such a spurious correlation disappears when using \mbh\ estimated from our formalisms.
学科主题天文学
语种中文
源URL[http://ir.ynao.ac.cn/handle/114a53/5088]  
专题云南天文台_高能天体物理研究组
推荐引用方式
GB/T 7714
王建国. 高红移星际尘埃与活动星系核中心黑洞质量[D]. 北京. 中国科学院研究生院(云南天文台). 2011.

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来源:云南天文台

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