爱因斯坦环及其星系团环境

该文研究了以星系作为透镜体产生的切向弧(即"爱因斯坦环")的强引力透镜现象,并对该领域近年来的观测和研究作了总结.对形成这些强引力透镜"环"的星系所进行的研究表明,其附近存在的质量所产生的会聚和剪切对透镜的质量分布模型非常敏感.在大视场巡天中找到的这种爱因斯坦环的数目相当多,大约是每平方度10个,其中"强引力透镜巡天"(Strong LensingLegacy Survey,SL2S)提供了大量处于星系团视场中的由椭圆星系产生的爱因斯坦环样本.系统地研究星系团外围存在的爱因斯坦环,一方面可以理解星系团环境对爱因斯坦环的影响,另一方面可以利用它们来探测星系团的物质分布,并进而对冷暗物质宇宙学提供新的探测方法.     

基于Shapelets基函数的引力透镜质量重构方法

引力透镜效应是探测星系团物质分布的有效方法之一.目前,利用引力透镜数据重构星系团质量分布的主流方法可以分为两大类,即参数法和非参数法.在实际研究工作中,受限于质量模型假设和计算分辨率等方面的影响,现有的重构算法仍有诸多亟需解决的问题.基于Shapelets基函数的引力透镜质量重构方法通过基函数来实现引力透镜质量重构,使用Shapelets基函数分解引力透镜势,以引力透镜中多重像的位置和背景星系椭率畸变为限制条件来迭代求解基函数系数从而得到透镜体的质量分布.通过拟合一个模拟的NFW (Navarro,Frenk and White)透镜系统测试了新方法的可行性,结果表明新方法可以在整体上重构出透镜体的质量分布,并拟合出接近真实的源位置,能够为星系团质量测量提供一套灵活且高效的重构算法.     

利用微引力透镜效应搜寻银河系内的重子暗物质

该文综述了利用微引力透镜效应来搜寻银河系内重子暗物质的原理、观测方法和结果以及当前国际上几个小组的工作和主要进展。简要回顾了对重子暗物质的认识过程，其中广泛分布于星系之中的暗天体被称为晕族大质量致密天体（MACHO）。综述了一些关于引力透镜的一些基本概念和基本公式，其中简单讨论了强引力透镜、弱引力透镜和微引力透镜的区别，并列出微引力透镜的两个重要参数光深和光变时标的定义及表达式。详细阐述了对于MACHO探测的方法和一些观测效应细节。综述了目前几个小组的工作，包括MACHO小组和EROS小组等，其中MACHO小组近来的工作得出MACHO为银晕的重要组成部分，其质量比例约为20％；而EROS最近工作得出的质量比例上限为7％。     

K_(ING)星系与类星体的引力透镜统计特性

本文以King模型去描述星系的引力透镜行为,把已知类星体作为光源,从统计上计算了引力透镜类星体对与其像间分离的关系。结果表明,星系的透镜行为不仅能解释全部透镜事例,而且可以揭示出星系的某些统计参数,如星系的最大质量、平均半径、平均核半径及质光比。宇宙中星系质量密度因子,Ω_g,亦可从中求得。     

引力透镜与类星体─星系(星系团)成协

综述了背景光源（类星体）与前方天体（星系、星系团等）成协的观测和统计事例．详尽叙述了与成协问题相关的引力透镜理论．全面介绍了对各种成协事例进行引力透镜理论解释的方法、研究现状及存在的问题．还给出了一种计算成协样品中面密度超出因子的改进方法．     

引力透镜与类星体——星系（星系团）成协

综述了背景光源（类星体）与前方天体（星系、星系团等）成协的观测和统计事例。详尽叙述了与成协问题相关的引力透镜理论。全面介绍了对各种成协事例进行引力透镜理论解释的方法、研究现状及存在的问题。还给出了一种计算成协样品中面密度超出因子的改进方法。     

引力透镜和弱引力透镜的新方法

引力透镜是天体物理中最重要的工具和手段之一,在宇宙学暗物质、暗能量、大尺度上的引力和系外行星探测中都发挥着巨大的作用.首先介绍了引力透镜的基本理论和近似,其次给出了引力透镜的主要发展历史,然后介绍了不同于光线偏折角的引力透镜理论新视角.之后评述了宇宙学中的弱引力透镜研究概况,简要回顾了弱引力透镜测量的主流方法宇宙剪切及...     

类星体对1146+111B,C是否为第七个引力透镜的像?

由于Hazard所发现的双类星体1146+111B,C有相同的红移和非常相似的光谱,故Paczynski和Turner等认为它们可能是一个新的天文引力透镜系统的候选者。这两个类星体在天空相距157角秒。如果进一步的观测能肯定它们确实是某天体的两个像,那么,它们可能具有到目前为止已观测到的引力透镜所成的像中最大的像间角距离。     

星系内禀指向对弱引力透镜剪切场信号污染的去除方法

星系的内禀指向(intrinsic alignment, IA)的关联性是弱引力透镜观测中剪切场信号的一个重要系统误差,人们在之前的弱引力透镜研究中已经提出了许多修正该误差的方法。从数据处理方面,人们可以剔除物理距离比较近的星系对,但是这种方法只能近似消除星系内禀指向自相关带来的污染项,并不能消除星系内禀指向与周围物质密度场的相关性,并且这种方法也会丢失很多星系的信息。而目前弱引力透镜观测中广泛使用的IA模型与实际的IA模型可能相差甚远,使用不同的IA模型得到的宇宙学参数会存在很大差别。虽然零调(nulling)技术不用假设IA模型,但是这种技术仅能消除星系内禀指向与周围物质密度场的相关性。另外,由于这种技术须对红移设置不同的权重,所以会失去IA对红移的依赖性。Zhang~([1, 2])提出的自修正方法,在不假设任何IA模型的情况下,利用多种观测量以及几个物理量之间的比例关系就能够把弱引力透镜中的IA信号很好地消除。此自修正方法可望广泛应用于即将开始的第四代弱引力透镜巡天中。     

光锥中强引力透镜的数值模拟

根据高精度宇宙学N体数值模拟输出的星系团以及星系团X射线光度和质量的经验关系:L-M,在红移区间(0.14,0.3)内构建了一个X射线波段流量限为3×10~(-19)J·s~(-1)·cm~(-2)(如Local Cluster Substructure Survey,缩写为LoCuSS )的大质量星系团样本。利用高分辨率的Ray-tracing数值模拟对包含真实观测信息(即红移、大小和形状)的COSMOS背景星系源进行单个透镜的成像模拟,并统计星系团不同投影方向的巨弧(即L/W10)产生效率。依据数值模拟立方体的尺度建立观测光锥,再根据光锥内不同红移区间所占立方体的体积比例用对应数量、红移的透镜对光锥进行随机填充,通过平均它们的透镜效率,最终计算得到光锥内的平均强引力透镜效率为3.22_(-1.47)~(+2.73)×10~(-2)。     

Search for gravitational lenses near the extragalactic double object CSL-1

We consider additional arguments in favor of the first observable cosmic string. We discuss candidates for gravitational lensing events near the extragalactic double source CSL-1 (Capodimonte-Sternberg-Lens Candidate no. 1) discovered in the Osservatorio Astronomico di Capodimonte Deep Field (OACDF). The detected excess of candidates for such events cannot be explained in terms of the theory of gravitational lensing by standard extragalactic objects (galaxies, groups of galaxies, etc.) and is in close agreement with the proposed model of gravitational lensing by a cosmic string.     

Random gravitational lensing

A simple three-dimensional approach to calculate the probability of observing gravitational lensing, caused by a chance superposition of lens and source, is presented. The formalism is then used to estimate the lensing probabilities in a number of astrophysical situations. As indicated in earlier works, we find that the chance of random gravitational lensing being detected locally is small, and the chance at extra-galactic distances is large.     

Gravitational lensing in quasar samples

The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This phenomenon had been predicted some 70 years earlier as a consequence of General Relativity. We present here a summary of what we have learnt since. The applications are so numerous that we had to concentrate on a few selected aspects of this new field of research. This review is focused on strong gravitational lensing, i.e. the formation of multiple images, in QSO samples. It is intended to give the reader an up-to-date status of the observations and to present an overview of its most interesting potential applications in cosmology and astrophysics, as well as numerous important results achieved so far. The first section follows an intuitive approach to the basics of gravitational lensing and is developed in view of our interest in multiply imaged quasars. The astrophysical and cosmological applications of gravitational lensing are outlined in Sect. 2 and the most important results are presented in Sect. 5. Sections 3 and 4 are devoted to the observations. Finally, conclusions are summarized in the last section. We have tried to avoid duplication with existing (and excellent) introductions to the field of gravitational lensing. For this reason, we did not concentrate on the individual properties of specific lens models, as these are already well presented in Narayan and Bartelmann (1996) and on a more intuitive ground in Refsdal and Surdej (1994). Wambsganss (1998) proposes a broad view on gravitational lensing in astronomy; the reviews by Fort and Mellier (1994) and Hattori et al. (1999) deal with lensing by galaxy clusters; microlensing in the Galaxy and the local group is reviewed by Paczyński (1996) and a general panorama on weak lensing is given by Bartelmann and Schneider (1999) and Mellier (1999). The monograph on the theory of gravitational lensing by Schneider, Ehlers and Falco (1992) also remains a reference in the field. Received 4 April 2000 / Published online 9 August 2000     

Angular cross-correlation of galaxies: a probe of gravitational lensing by large-scale structure

The angular cross-correlation between two galaxy samples separated in redshift is shown to be a useful measure of weak lensing by large-scale structure. Angular correlations in faint galaxies arise as a result of spatial clustering of the galaxies as well as gravitational lensing by dark matter along the line of sight. The lensing contribution to the two-point autocorrelation function is typically small compared with the gravitational clustering. However, the cross-correlation between two galaxy samples is almost unaffected by gravitational clustering provided that their redshift distributions do not overlap. The cross-correlation is then induced by magnification bias resulting from lensing by large-scale structure. We compute the expected amplitude of the cross-correlation for popular theoretical models of structure formation. For two populations with mean redshifts of ≃0.3 and 1, we find a cross-correlation signal of ≃1 per cent on arcmin scales and ≃3 per cent on scales of a few arcsec. The dependence on the cosmological parameters Ω and Λ, the dark matter power spectrum and the bias factor of the foreground galaxy population is explored.     

CLASS B2108+213: a new wide-separation gravitational lens system

We present observations of CLASS B2108+213, the widest separation gravitational lens system discovered by the Cosmic Lens All-Sky Survey. Radio imaging using the VLA at 8.46 GHz and MERLIN at 5 GHz shows two compact components separated by 4.56 arcsec with a faint third component in between which we believe is emission from a lensing galaxy. 5-GHz VLBA observations reveal milliarcsecond-scale structure in the two lensed images that is consistent with gravitational lensing. Optical emission from the two lensed images and two lensing galaxies within the Einstein radius is detected in Hubble Space Telescope imaging. Furthermore, an optical gravitational arc, associated with the strongest lensed component, has been detected. Surrounding the system is a number of faint galaxies which may help explain the wide image separation. A plausible mass distribution model for CLASS B2108+213 is also presented.     

Close separation triple system QSO 1009-0252 with discordant redshifts: Is the spectrum of one component blueshifted?

1009-0252 is a Quasi Stellar Object (QSO) with three components A, B, C. A, B are thought to be the result of gravitational lensing of one object, and A, C constitute a close pair with redshifts 2.74 and 1.62 respectively. Close separation pairs of QSOs with discordant redshifts have received special attention in recent years, probably because of the possibility that they may be physically associated, implying non-cosmological redshifts. Attempts have been made to explain their occurrences due to the effect of gravitational lensing. However, gravitational lensing has not offered a completely satisfactory explanation for this triplet. Furthermore, examination revealed some inadequacies and inconsistencies in the redshift identification of the observed lines in the component A. Observational results of 1009-0252 therefore remain puzzling. We propose an alternative explanation by suggesting that A, B actually constitute a close pair and C is an unrelated object in the field. We show that the observed spectrum of A can be interpreted as blueshifted. This implies that A, B are two separate objects, one (A) approaching us and the other (B) receding from us, and are not the result of gravitational lensing of a single object. The oppositely directed pair A, B may have been ejected due to the merger of two galaxies.     

A complete infrared Einstein ring in the gravitational lens system B1938 + 666

We report the discovery, using NICMOS on the Hubble Space Telescope , of an arcsec-diameter Einstein ring in the gravitational lens system B1938+666. The lensing galaxy is also detected, and is most likely an early-type galaxy. Modelling of the ring is presented and compared with the radio structure from MERLIN maps. We show that the Einstein ring is consistent with the gravitational lensing of an extended infrared component, centred between the two radio components.     

Gravitational Lensing

In the roughly 20 years of its existence as an observational science, gravitational lensing has established itself as a valuable tool in many astrophysical fields. In the introduction of this review we briefly present the basics of lensing. Then it is shown that the two propagation effects, lensing and scintillation, have a number of properties in common. In the main part various lensing phenomena are discussed with emphasis on recent observations. This revised version was published online in July 2006 with corrections to the Cover Date.