Investigation and Analysis of Doppler Redshifts of Quasars
学位专业
天体物理
中文摘要
本文综述类星体的观测和理论研究现状，详细介绍本人在攻读博士学位期间在类星体多普勒红移方面的研究工作。 类星体吸收线的研究具有重要意义。一方面，对内禀吸收线的研究有助于我们了解类星体的结构和其上发生的物理过程。另一方面，类星体是迄今为止观测到的离我们最遥远的天体之一，对插入天体产生的吸收线的研究使我们能够了解广阔时空范围内的物质和运动，有助于了解星系的形成和演化以及宇宙大尺度结构等，因而具有宇宙学意义。 类星体吸收线的情况非常复杂。类星体吸收线中，大部分吸收系统的红移小于类星体的红移，即zabszem情形少有研究。我们认为这种情形是由于吸收体朝类星体运动从而产生多普勒红移，吸收体的宇宙学红移与其多普勒红移叠加就出现吸收体红移大于类星体红移的情形。我们通过从一个类星体吸收线大样本中抽出123个具有zabs>zem的类星体，共得到256个吸收系统，然后按公式zDopp=(zabs-zem)/(1+zem)来计算每个吸收系统的多普勒红移。从这256个吸收系统多普勒红移的分布我们发现在分布中存在两个峰，第一个在zDopp≈0.00，第二个在zDopp≈0.01。第二个峰对应的多普勒速度大约是3000 km s-1。我们猜想具有大的多普勒红移的类星体可能比其它类星体的质量更大，对在该天体附近运动的物体产生的引力也越大，因此产生的多普勒速度也越大。由于这类天体质量大，我们猜想它们应该更亮。我们把所用的类星体表按多普勒红移分成3组对它们光度分布进行统计分析，同时作K-S检验。结果显示，在统计意义上，大多普勒红移的类星体确实比其它类星体亮，而小多普勒红移的类星体则与其它类星体在亮度分布上没有统计意义上的差别。该结果支持了我们的猜想。 我们这一工作的主要分析过程和结果是：通过对多普勒红移分布中第二个峰的分析揭示类星体中存在一个子类，这类类星体具有特征：1、他们的多普勒红移大于0.0088；2、它们普遍比其它类星体亮；3、他们的多普勒速度集中在3000 km s-1。据此，对于大的正多普勒红移（zabs>zem）情形我们给出如下解释：具有较大zabs>zem数值的吸收系统是内禀的，由相对运动造成的；这些吸收体正朝着类星体的中心下落；下落速度大约为3000 km s-1。 此外，我们还对吸收体的空间分布进行了初步探讨。我们从一个吸收线大样本中抽出Mg II、Fe II、C IV、HI、LLS、DLA六种吸收体，计算其多普勒红移并作其分布。我们发现Mg II和Fe II吸收体在宇宙空间中的分布可能是均匀的；而LLS吸收系统在空间中的分布则与类星体的空间分布相似。这与LLS的每单位间隔红移内吸收体数随红移演化的关系符合得较好。H I 吸收体似乎都位于离类星体一个比较固定的距离。虽然我们的分析还没有得出结论，但初步的探讨暗示这个问题值得做进一步的分析研究。 我们还探讨了多普勒红移是否随红移而演化的问题。我们用256个正的多普勒红移与其对应的类星体的红移之间作相关分析。我们发现多普勒红移与类星体红移间存在弱正相关，如果承认这种相关性，那么多普勒红移就随类星体红移而演化。也就是说吸收体与类星体之间的相对运动在宇宙早期要比晚期剧烈。对这一问题的深入探讨也将是我们下一步要开展的工作。
英文摘要
We summarize the observational and theoretical studies of quasars, and present the results of our studies on the Doppler redshifts of quasars. It is particularly important to study the absorption lines of quasar. First, studies on intrinsic absorption lines can help us to understand the structure of quasars and the physical processes arising from them. On the other hand, quasars are one of the most distant objects observed so far, and studies on absorption lines arising from inserted objects enable us to understand the matter and motion within vast space-time range, the galactic formation and evolution and large-scale structure of the universe. The absorption lines of quasars are very complicated. Most of the redshifts of the absorption systems are smaller than the corresponding redshift of quasar, i.e. zabszem is seldom studied. We suspect that the phenomenon of absorption redshifts greater than their corresponding emission redshifts might be due to the fact that some absorbers are close to and move towards the quasars, and then the absorption redshifts contain their cosmological redshifts and Doppler redshifts. We extracted 256 absorption systems with absorption redshifts greater than the emission redshifts (zabs>zem). These absorption systems contain 123 quasars. We calculated their Doppler redshifts using zDopp= (zabs-zem)/ (1+zem) and then analyzed the data and found that there is a bi-peak structure in the distribution of Doppler redshifts, where one peak is located at zDopp=0.0 and the other one at zDopp=0.01. The second peak corresponds to a Doppler velocity of 3000 km s-1. We suspect that those having large Doppler redshift might be more massive. Massive quasars would possess larger gravity and therefore could produce larger Doppler velocities. Since they are more massive, they might be brighter. We divided quasars available in a quasar catalogue into three groups according to their Doppler redshifts and then performed a K-S test to the distributions of luminosities of the three groups of quasars. The results favor our supposal. Our main efforts and results are as follows. We analyzed the distribution of Doppler redshifts of quasars with zabs>zem and found a bi-peak structure in the distribution. Analyzing the second peak reveals that there is a sub-set of quasars, which has the following characteristics: 1) Their Doppler redshifts are greater than 0.0088; 2) They are found to be generally brighter than others; 3) The Doppler velocities of the absorbers of these quasars are concentrated at ～3000 km s-1. We presented an interpretation to the phenomenon of larger Doppler redshifts of quasars with zabs>zem: absorption systems with large values of zabs-zem are due to relative motions and the absorbers are falling towards the central region of quasars with a velocity of ～3000 km s-1. In addition, we discussed the distributions of quasar absorbers with all absorption redshifts in space. We calculated the Doppler redshifts (the extended Doppler redshifts defined in Qin et al. 2004) of six kinds of absorbers, Mg II, Fe II, C IV, HI, LLS and DLA, available in a large absorption lines sample. From the distributions of their Doppler redshifts, we find that Mg II and Fe II absorbers are probably homogeneous distributions in the universe. The distributions of Lyman limits in the universe may be the same as those of quasars. This agrees with the evolution relationship between the number of absorbers per unit redshift and redshift for Lyman limits. H I absorbers are likely having a constant distance to the quasars. It deserves a further investigation. The issue of whether there is an evolution relationship between Doppler redshifts of quasars and cosmological redshifts was also discussed. A linear correlation analysis between 256 positive Doppler redshifts and their cosmological redshifts shows that there is a weak correlation between Doppler redshifts and their cosmological redshifts. The evolution of Doppler redshifts suggests that the relative motions between the close absorbers and the corresponding quasars might be more violent at the early epoch of the universe than at the late epoch. A detailed analysis on this issue is included in our plan.
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