水脉泽寄主星系的Spitzer中红外特性研究

截至目前,在已搜寻过的5 000多个星系中,只在180多个星系中探测到水脉泽辐射,这种脉泽的绝大多数与活动星系核(AGN)辐射相关.文章利用先进的红外卫星Spitzer对水脉泽星系样本多个波段的观测资料(3.6μm、4.5μm、5.8μm、8.0μm和24.0μm),计算得到该样本的红外辐射光度、谱指数等物理参量.通过统计对比分析水脉泽寄主星系和非水脉泽寄主星系在各个波段的辐射光度和谱指数、中红外能谱分布,结果显示:①水脉泽星系有较大的中红外光度,尤其在长波24μm波段更为明显;②水脉泽和非水脉泽星系的谱指数与能谱分布没有明显区别;③水脉泽光度与其寄主星系的中红外光度统计显示没有明显的相关性.研究结果为将来水脉泽的搜寻工作提供可能的选源指导.     

SDSSDR9星系对中恒星形成速率的测量与研究

星系演化是天体物理研究领域的重要课题和前沿之一.其中,星系并合演化理论在其中具有至关重要的地位.恒星形成速率是这一研究的重要参数之一.近些年来,对于恒星形成速率测量方法的研究更是取得了长足的进展.本论文选取了SDSS DR9中0z≤0.3的3 444个星系对以及4 000个场星系作为样本,通过对恒星形成速率的计算来对比研究星系相互作用对星系演化所起的作用.     

环境对于旋涡星系气体的影响研究

星系的演化会受到各种因素的影响,如星系团介质的压力作用、邻近星系的潮汐力作用、星系之间的碰撞等。因此处在不同环境内的星系,它们的形态、颜色以及气体含量上必然存在一定的差异。选取了位于星系群中的样本星系和空洞环境里面的空洞旋涡星系(Void spiral galaxies)、密度较低的环境内的孤立旋涡星系(Isolated spiral galaxies)以及位于室女星系团(Virgo Cluster)内的室女旋涡星系的多波段测光数据,对比研究了不同环境里旋涡星系之间的颜色差异、气体含量、星系的恒星质量等特征,并讨论了其可能的产生机制。     

基于Spitzer数据的羟基脉泽寄主星系的中红外特性研究

目前发现羟基脉泽的星系都为亮或极亮的红外星系,但在许多(极)亮红外星系中并未探测到羟基脉泽辐射,这可能意味着羟基脉泽寄主(极)亮红外星系具有某些独特的特性.文章利用Spitzer红外卫星的测光数据,研究羟基脉泽寄主星系的中红外特性.通过统计对比分析羟基脉泽寄主星系和非羟基脉泽寄主星系(即未探测到羟基脉泽辐射的星系)在3. 6μm、4. 5μm、5. 8μm、8μm和24μm波段的辐射光度和谱指数、中红外能谱分布,及其与羟基脉泽光度的关系,结果发现:(1)非羟基脉泽样本的3. 6μm辐射光度明显大于羟基脉泽样本;(2)羟基脉泽样本的谱指数较大,能谱分布的对比显示羟基脉泽的光谱更陡(8μm～24μm);(3)羟基脉泽光度与中红外24μm的光度存在较弱的正相关(R～0. 36),间接支持羟基脉泽辐射的远红外辐射抽运机制.     

远红外亮类星体的研究进展

远红外亮类星体是极亮红外星系中具有I型活动星系核光谱特征的天体,光学光谱研究表明它们在光学波段的辐射主要由中心活动星系核主导,其中心超大质量黑洞的质量为107~108M☉,且有超爱丁顿吸积率.与光学选类星体相比,远红外亮类星体在远红外波段存在明显的辐射超出,这可能是由其核区周围~1 kpc尺度内的星暴活动(恒星形成率约为几百M☉yr-1)加热尘埃造成.对分子气体进行观测发现远红外亮类星体的宿主星系中存在约109~1010M☉的分子气体,这些分子气体可以为黑洞和核球的增长提供"原料".几乎所有远红外亮类星体都处于富气星系并合的晚期,是极亮红外星系向光学选类星体演化的过渡天体.     

低红移活动星系核中大质量黑洞与核球质量关系研究

采用活动星系核图像的核球/盘分解数据得到核球R波段光度值,计算了一个X射线活动星系核样本的中心大质量黑洞质量与核球质量之比(Mbh/Mbulge),其中包括15个窄线塞弗特1星系(NLS1 s)和18个宽线塞弗特1星系(BLS1 s).我们发现log(Mbh/Mbulge)的平均值,对15个窄线塞弗特1星系为:-3.81±0.11;而对18个宽线塞弗特1星系,则为:-2.91±0.13.这表明:窄线塞弗特1星系相对于宽线塞弗特1星系而言有较低的Mbh/Mbulge.     

用紫外线看宇宙——紫外线观测卫星GALEX获得的最新照片

用紫外线波段观测刚形成不久的年轻星系，它们看起来是明亮的天体。美国宇航局发射的星系演化探测卫星，就是专门用来对年轻星系进行紫外线观测，探索星系演化的一座太空天文台。星系演化探测卫星对宇宙进行的观测，获得了十分宝贵的资料，甚至有助于揭示我们所居住的银河系当初是如何形成的。     

中红外选活动星系核中水脉泽辐射的搜寻

之前的研究显示水超脉泽辐射更倾向位于被物质严重遮掩的活动星系核中,因此,作者选择了一个活动星系核样本,开展水超脉泽的搜寻工作.该样本主要基于它们的中红外辐射特性(谱和颜色特性)而被证认为活动星系核,并由于被严重遮掩而未能在之前的光学观测中被证认.作者申请并获准应用德国Effelsberg 100 m口径望远镜,于2014年1月开展了水超脉泽的搜寻工作.观测结果显示只有几个源的谱存在可能的脉泽辐射,根据观测结果的噪声水平和这些星系的距离,作者估算了每个源的水脉泽辐射光度的上限值,这将对以后更高灵敏度的搜寻工作提供指导.     

基于积分场光谱数据的近邻星系恒星形成区多波段恒星形成率定标研究

为探究多波段数据相结合的恒星形成率定标在近邻星系恒星形成区的可应用性,基于窄带Hα成像观测数据、二维积分场光谱数据(IFS)以及Spitzer/MIPS 24μm和Herschel/PACS 70、100、160μm的中远红外波段高空间分辨率图像,对5个近邻恒星形成星系中119个恒星形成区进行恒星形成率定标研究.以由IFS数据测得的巴尔末减缩得到的内部消光改正后的Hα光度为基准,将24、70、100和160μm与未经过内部消光改正的Hα光度相结合进行定标.结果发现:在1034~1039 erg/s光度范围内,4个红外波段与Hα光度的结合均能很好地示踪经过内部消光改正的Hα光度,RMS为0.20~0.27 dex.良好的数据分布表明基于较小样本的研究结果具有统计意义和可应用性.     

对NGC5128星系50 kpc内表面亮度轮廓的研究

NGC5128是距离地球最近的、可通过地面望远镜直接分辨其中红巨星分支恒星的巨椭球星系。通过分辨并计数该星系外晕中的红巨星分支恒星, 研究其星系晕的表面亮度轮廓, 并对位于该星系外恒星晕主轴方向的内外两个视场的图像进行测光研究, 这些CCD图像来自Magellan/IMACS f/4望远镜的V和I两个波段。通过星等和颜色对红巨星分支恒星进行筛选, 最终在两个视场的图像中分别得到包含4719和980个红巨星分支恒星候选的样本, 并将外场样本用于对内场污染的估计和矫正。采用 Sersic定律对内场表面亮度轮廓进行拟合, 得到的最佳拟合参数为: V波段, r_e = 6.21角分, μ_e = 22.05 mag/arcsec², n = 1.90, 拟合误差为0.37星等; I波段, r_e = 6.57角分, μ_e =20.79 mag/arcsec², n = 1.90, 拟合误差为0.41星等。结果显示V和I波段的拟合结果一致, 并且在数据的精度内, 没有发现轮廓向晕族突变的迹象。     

A close nuclear black-hole pair in the spiral galaxy NGC 3393

The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging. Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years (refs 2 and 3; 1 parsec = 3.26 light years) and exemplify the first stages of this gravitational interaction. The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation (such as NGC 6240 with a separation of about 2,600 light years and Mrk 463 with a separation of about 13,000 light years between the nuclei) demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution; such mergers lead to an elliptical galaxy, as in the case of the double-radio-nucleus elliptical galaxy 0402+379 (with a separation of about 24 light years between the nuclei). Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. Here we report the presence of two active massive black holes, separated by about 490 light years, in the Seyfert galaxy NGC 3393 (50 Mpc, about 160 million light years). The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution. Comparison of our observations with current theoretical models of mergers suggests that they are the result of minor merger evolution.     

Galaxies appear simpler than expected

Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment and feedback from supernova explosions and supermassive black holes. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular momentum, baryon fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free from optical selection effects, shows five independent correlations among six independent observables, despite having a wide range of properties. This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our data set. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter model in cosmology.     

A2142星系团子结构中的星系演化

系统整理了星系团A2142的光谱和测光数据．利用花树算法得到的子结构,将星系团视场中的星系分为非子结构、子结构和外围星系3类．通过研究它们的分布、产星活动、D_n4000等物理信息,发现了A2142星系团中的星系存在明显的径向演化趋势．星系从星系团外围落入团中心的过程中,其演化不仅受到星系团内介质的影响,还受到子结构自身的调制．      

The rapid formation of a large rotating disk galaxy three billion years after the Big Bang

Observations and theoretical simulations have established a framework for galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark-matter haloes; mergers of haloes and galaxies then led to the hierarchical build-up of galaxy mass. It remains unclear, however, over what timescales galaxies were assembled and when and how bulges and disks--the primary components of present-day galaxies--were formed. It is also puzzling that the most massive galaxies were more abundant and were forming stars more rapidly at early epochs than expected from models. Here we report high-angular-resolution observations of a representative luminous star-forming galaxy when the Universe was only 20% of its current age. A large and massive rotating protodisk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole. The high surface densities of gas, the high rate of star formation and the moderately young stellar ages suggest rapid assembly, fragmentation and conversion to stars of an initially very gas-rich protodisk, with no obvious evidence for a major merger.     

Host-plant adaptation drives the parallel evolution of reproductive isolation

Parallel evolution of similar traits in independent populations that inhabit ecologically similar environments strongly implicates natural selection as the cause of evolution. Parallel speciation is a special form of parallel evolution where traits that determine reproductive isolation evolve repeatedly, in closely related populations, as by-products of adaptation to ecological conditions. The outcome of such parallel evolution is that ecologically divergent pairs of populations exhibit greater levels of reproductive isolation than ecologically similar pairs of populations of a similar or younger age. The parallel evolution of reproductive isolation provides strong evidence for natural selection in the process of speciation, but only one conclusive example from nature is known. Populations of the walking-stick insect Timema cristinae that use different host-plant species have diverged in body size and shape, host preference, behaviour and the relative frequency of two highly cryptic colour-pattern morphs. Here we report that divergent selection for host adaptation, and not genetic drift, has promoted the parallel evolution of sexual isolation in this species. Our findings represent a clear demonstration that host-plant adaptation can play a crucial and repeatable role in the early stages of speciation.     

Rapid evolution of the most luminous galaxies during the first 900 million years

The first 900 million years (Myr) to redshift z approximately 6 (the first seven per cent of the age of the Universe) remains largely unexplored for the formation of galaxies. Large samples of galaxies have been found at z approximately 6 (refs 1-4) but detections at earlier times are uncertain and unreliable. It is not at all clear how galaxies built up from the first stars when the Universe was about 300 Myr old (z approximately 12-15) to z approximately 6, just 600 Myr later. Here we report the results of a search for galaxies at z approximately 7-8, about 700 Myr after the Big Bang, using the deepest near-infrared and optical images ever taken. Under conservative selection criteria we find only one candidate galaxy at z approximately 7-8, where ten would be expected if there were no evolution in the galaxy population between z approximately 7-8 and z approximately 6. Using less conservative criteria, there are four candidates, where 17 would be expected with no evolution. This demonstrates that very luminous galaxies are quite rare 700 Myr after the Big Bang. The simplest explanation is that the Universe is just too young to have built up many luminous galaxies at z approximately 7-8 by the hierarchical merging of small galaxies.     

KMM算法在星系团研究中的应用

介绍了KMM算法基本原理,并将此算法运用于近邻双星系团系统A399/A401.KMM算法对该系统中的215颗星系进行了成员判定,其中127颗星系属于A401,88颗星系属于A399.实践表明,KMM算法在研究星系团动力学演化方面很有效.     

活动星系核的演化研究

活动星系核的演化研究在能量产生、辐射机制等基本问题的研究中占有重要的地位。首先对活动星系核的基本性质及分类进行了简单的介绍,然后根据搜集到的数据,通过分析发光度、中心黑洞质量、吸积率与红移的关系图,进一步支持了活动星系核的演化存在的两个演化序列的观点:一个是平谱射电类星体FSRQ逐步过渡到BL Lac天体,然后过渡到射电星系RG,最后过渡到椭圆星系;另一个是从类星体Quasars过渡Seyfert星系,然后过渡到正常漩涡星系。     

An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10

Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way. The birth and growth of the first 'seed' black holes in the earlier Universe, however, is observationally unconstrained and we are only beginning to piece together a scenario for their subsequent evolution. Here we report that the nearby dwarf starburst galaxy Henize?2-10 (refs 5 and 6) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize?2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize?2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.