共查询到20条相似文献，搜索用时 46 毫秒
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根据２５μｍ和６０μｍ间的红外谱指数及６０μｍ和１００μｍ的相对流量选择了６个天体，在１９９４年９月９日至１１日期间，利用北京天台２．１６ｍ望远镜观测了它们的光谱，经处理后，发现了一个新的Ｓｅｙｆｅｒｔ ２和一个Ｓｅｙｆｅｒｔ３星系，另外还有一个ＨＩＩ星系。 相似文献
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Cai-Na Hao Xiao-Yang Xia Shu-De Mao Zu-Gan Deng Hong Wu 《天体物理学报》2008,8(1):12-24
We study the growth of black holes and stellar population in spheroids at high redshift using several （sub）mm-loud QSO samples. Applying the same criteria established in an earlier work, we find that, similar to IR QSOs at low redshift, the far-infrared emission of these （sub）mm-loud QSOs mainly originates from dust heated by starbursts. By combining low-z IR QSOs and high-z （sub）mm-loud QSOs, we find a trend that the star formation rate （M＊） increases with the accretion rate （Mace）. We compare the values of M＊/Macc for submm emitting galaxies （SMGs）, far-infrared ultraluminous/hypeduminous QSOs and typical QSOs, and construct a likely evolution scenario for these objects. The （sub）mm-loud QSO transition phase has both high Macc and M＊ and hence is important for establishing the correlation between the masses of black holes and spheroids. 相似文献
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Dan Wang Yan-Xia Zhang Chao Liu Yong-Heng Zhao 《天体物理学报》2008,8(1):119-126
We investigate two training-set methods; support vector machines （SVMs） and Kernel Regression （KR） for photometric redshift estimation with the data from the databases of Sloan Digital Sky Survey Data Release 5 and Two Micron All Sky Survey. We probe the performances of SVMs and KR for different input patterns. Our experiments show that with more parameters considered, the accuracy does not always increase, and only when appropriate parameters are chosen, the accuracy can improve. For different approaches, the best input pattern is different. With different parameters as input, the optimal bandwidth is dissimilar for KR. The rms errors of photometric redshifts based on SVM and KR methods are less than 0.03 and 0.02, respectively. Strengths and weaknesses of the two approaches are summarized. Compared to other methods of estimating photometric redshifts, they show their superiorities, especially KR, in terms of accuracy. 相似文献
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Jian-Ling Wang 《中国天文和天体物理学报》2008,8(6)
We used the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) to study the morphological properties of 1137 nearby infrared (IR) galaxies, most of which are brighter than 15.9 mag in r-band. This sample was drawn from a cross-correlation of the Infra-Red Astronomical Satellite (IRAS) point source catalog redshift survey with DR5 at z(≤)0.08. Based on this IR galaxy sample, we constructed five volume-limited sub-samples with IR luminosity ranging from 109.5L⊙ to 1012L⊙. By deriving the IR luminosity functions (LF) for different morphological types, we found that normal spiral galaxies are the dominant population below LIR～ 8 × 1010 L⊙; while the fraction of barred spiral galaxies increases with increasing IR luminosity and becomes dominant in spiral galaxies beyond LIR(≈) 5×1010L⊙. As the IR luminosity decreases, the IR galaxies become more compact and have lower stellar masses. The analysis also shows that normal spiral galaxies give the dominant contribution to the total comoving IR energy density in the nearby universe, while, in contrast, the contribution from peculiar galaxies is only 39%. 相似文献
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极红天体(EROs)是指利用光学和近红外两个波段的色指数(如I-K4 mag)挑选出来的一类星系。研究表明极红天体可分为两类:一类是被大量尘埃红化的高红移恒星形成星系,主要是较年轻的旋涡或不规则星系,有恒星正在形成,称为DGs;另一类是由年老星族(≥1 Ga)主导的高红移椭圆星系,基本上没有或仅有弱的恒星形成,简称为OGs。极红天体中这两种不同类型的星系,很可能是近邻大质量星系的前身星系,只是分别代表着不同的形成历史。介绍了不同类型极红天体的各种物理性质的研究进展,如形态和结构、光谱特征、成团性、红移分布和星系计数等,以及阐述了该领域未来的研究方向。 相似文献
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Two-dimensional bulge/disk light decomposition with GIM2D in both the r-and g-bands has been applied to a sample of 129 early-type galaxies brighter than 13.5 magnitude in the r-band,selected from the Sloan Digital Sky Survey Data Release 2.Intensity-weighted Fourier coefficient (a4/a) was also derived for each sample galaxy.Our analysis shows that and between bulge and disk scale sizes.Isophotal shape parameter (a4/a) is not correlated with BIT and nB.Both bulge and disk components satisfy a color-magnitude relation.The k space Fundamental Plane analysis shows that galaxies with larger B/T tend to lie tighter and closer to the line of k1 k2=8 (the so-called "zone of avoidance") than the galaxies with smaller B/T.It indicates that existence of the disk component may lead to scatter of the distribution on the Fundamental Plane.Our analysis also shows that k1 k2 correlates with (y-r) color and B/T,but does not correlate with (a4/a) for early-type galaxies.The fitted parameters and other retrieved parameters used in this paper for all sample galaxies are available online. 相似文献
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Ｈｅｌｏｕ将双星系中的自旋方向的统计研究方法用到星系形成过程中,发现旋涡星系的自旋是反相关的,由此联想到在由星系并合过程中自旋对轨道倾角的依赖性。将Ａａｒｓｅｔｈ的标准Ｎ体模拟程序加上动力摩擦,形成一个研究星系并合的Ｎ体模拟程序,用来研究小星系群中星系的自旋和轨道倾角的依赖性。结果表明,在小星系群中,的确存在着类似旋涡星系中的自旋和轨道倾角的反相关性。 相似文献
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We present a study of the nearby Seyfert galaxy NGC 3982 using optical,infrared and X-ray data acquired by SDSS,Spitzer and Chandra.Our main results are as follows:(1) A simple stellar population synthesis on the nuclear and circumnuclear SDSS spectra gives unambiguous evidence of young stellar components in both the nuclear and circumnuclear regions.(2) The Spitzer Infrared Spectrograph (IRS) spectrum of the central region (～3") shows a power-law continuum,a silicate emission feature at 9.7 μm,and significant PAH emission features at 7.7,8.6,11.3 and 12.7/zm,suggesting the coexistence of AGN and starburst activities in the central region of NGC 3982.(3) We estimate the star formation rate (SFR) of the circumnuclear (～5"-20") region from the Ha luminosity to be for the active nucleus of NGC 3982 from radio to X-ray,and obtain a bolometric luminosity of Lbol=4.5×1042 erg s-1,corresponding to an Eddington ratio (Lbol/LEdd) of 0.014.The HST image of NGC 3982 shows a nuclear mini-spiral between the circumnuclear starforming region and the nucleus,which could be the channel through which gas is transported to the supermassive black hole from the circumnuclear star-forming region. 相似文献
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Xiao-Yan Chen Cai-Na Hao Jing Wang 《天体物理学报》2008,8(1):25-38
We compare the ionized gas velocity dispersion σgas with the stellar velocity dispersion σ＊ in star-forming galaxies, composite galaxies, Low Ionization Nuclear Emissionline Regions （LINERs） and Seyfert 2s, compiled from a cross-identification of Sloan Digital Sky Survey Fourth Data Release （SDSS DR4） and Point Source Catalogue Redshift Survey （PSCz）. We measure σgas from the FWHMs of emission lines （Hα, [NⅡ]λλ6548, 6583 and [SⅡ]λλ6716, 6731）. A significant correlation between the gas and stellar velocity dispersion exists, despite substantial scatter. The mean value of the gas to stellar velocity dispersion ratio is close to unity. This suggests that gas velocity dispersion can substitute for the stellar velocity dispersion as a tracer of the gravitational potential well for all the four types of galaxies, but the involved uncertainties are different from type to type. We also studied -↑σgas, as a function of the redshift and the axial ratio to test the effects of aperture and galaxy inclination, and found that both effects are weak. Finally we checked the trend of -↑σgas/σ＊ with the infrared luminosity and found no significant correlation. 相似文献
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在１９９２年３月３１日至４月２日期间，我们利用云南天文台１ｍ望远镜２号ＣＣＤ和缩焦装置，对环星系ＮＧＣ４７３６进行了Ⅴ和Ⅰ波段深曝光观测。在经过Ｒｉｃｈａｒｄｓｏｎ－Ｌｕｃｙ图象复原以及自适应滤波两种方法处理后，发现仅仅在Ⅴ波段图象上，其核区存在一个直径约为１０″的环状结构。 相似文献
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从1981年开始,北京天文台开展了发射线星系的物端稜镜巡天。用60/90cm Schmidt望远镜加5.°3的物端稜镜在敏化的ⅢaJ底片上可以得到亮于16~m的星系光谱像。本文公布了第一批巡天结果:在覆盖天区约220平方度的12张底片上证认出50个发射线天体,47个河外星系(其中3个可能是新的Seyfert星系),3个行星状星云(其中一个N2242以前被当作河外星系)。文中给出了这些天体的名称、坐标、星等及光谱结构分类等资料,并比较系统地讨论了发射线星系的证认及光谱结构分类。我们还将本巡天的结果与其他天文台的结果作了比较。这些天体的证认图见图版Ⅰ—Ⅱ。 相似文献
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本文对CfA样本中的属群星系进行了最近邻间距分析,发现在最近邻距离小于20kpc的星系中存在明显的Seyfert核超(即其中Seyfert星系所占比率高出平均值约3倍)。这表明近距星系的存在可能是产生Seyfert核活动的有利环境。 相似文献
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盘星系的内禀扁度对计算星系的空间倾角非常重要．对从LEDA数据库中选取的14988个盘星系进行内禀扁度的统计分析．研究表明，盘星系的内禀扁度与星系的形态密切相关．整体上说，透镜星系和不规则星系的内禀扁度qo大于旋涡星系，早型旋涡星系的内禀扁度qo大于晚型旋涡星系，其中Scd星系的内禀扁度qo最小．利用所得的qo-T关系，还对16个已知倾角的亮星系进行了倾角计算，发现与其他方法估计的空间倾角符合得较好． 相似文献
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It is well accepted that feedback from active galactic nuclei (AGNs) plays an important role in the coevolution of the supermassive black hole (SMBH) and its host galaxy,but the concrete mechanism of feedback remains unclear.A considerable body of evidence suggests that AGN feedback suppresses star formation in the host galaxy.We assemble a sample of Seyfert 2 galaxies with recent observational data of compact nuclear starbursts and estimate the gas surface density as a function of column density to illuminate the relation between feedback and AGN properties.Although there are some uncertainties,our data still imply the deviation from the star formation law (Kennicutt-Schmidt law).Further,they indicate that:(1) Feedback correlates with the Eddington ratio,rather than with the mass of SMBH,as a result of decreasing star formation efficiency.(2) The SMBH and the torus are probably undergoing coevolution.Conclusions presented here can be refined through future high resolution CO or HCN observations. 相似文献
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从星系形成和演化的角度出发，对星系结构和动力学进行的粗略的评述，内容包括：（1）初步描述了星系中各主要成分的物理特征（空间分布，运行学和化学）及其形成和演化，（2）Damped Lyman-alpha systems(DLAs)是本地星系的化石，对其进行观测研究是HST的主要任务之一，对DLAs宽的谱线轮廓的物理机制和其恒星形成，化学演化进行了讨论，（3）目前已证明Lyman Break方法是发现高红移高恒星形成星系的有效手段，讨论了Lyman Break Galaxies的动力学过程和恒星形象，（4）旋涡星系和椭圆星系的Scaling Law是星系形成和演化所必须解释的问题，对近期该方面的研究结果作了介绍，（5）整体超星的反馈作用在星系形成和演化中起了重要作用，评述了该物理过程对星系演化的影响；（6）随着观测资料的不断积累，各种物体对河外背景辐射的贡献已成了一个重要的研究方向，讨论了宇宙整体的星形成历史和化学演化，（7）银河系是进行星系形成和演化研究的归算零点，介绍了银河系的结构，动力学及演化。 相似文献
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Xu Kong Wei Zhang Min Wang 《天体物理学报》2008,8(1):1-11
Using a simple color selection based on B-, z- and K-band photometry, BzK =（z - K）AB - （B - Z）AB 〉 -0.2, we picked out 52 star-forming galaxies at 1.4 ≤z ≤ 2.5 （sBzKs） from a K-band selected sample （Kvega 〈 22.0） in an area of - 5.5 arcmin^2 of the Hubble Ultra Deep Field （UDF）. We develop a new photometric redshift method, and the error in our photometric redshifts is less than 0.02（1 ＋ z）. From the photometric redshift distribution, we find the BzK color criterion can be used to select star-forming galaxies at 1.4≤ z ≤ 2.5 with Kvega 〈 22.0. Down to Kvega 〈 22.0, the number counts of sBzKs increase linearly with the K magnitude; the sBzKs are strongly clustered, and most of them have irregular morphologies on the ACS images. They have a median reddening of E（B - V） - 0.28, an average star formation rate of - 36 M⊙ yr^-1 and a typical stellar mass of - 10^10 M⊙. The UV criterion for the galaxies at z - 2 can select most of the faint sBzKs in the UDF, but it does not work well for bright, massive, highly-reddened, actively star-forming galaxies. 相似文献
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刘步林 《中国天文和天体物理学报》1999,(1)
Ｈｅｌｏｕ将双星系中的自旋方向的统计研究方法用到星系形成过程中,发现旋涡星系的自旋是反相关的,由此联想到在由星系并合过程中自旋对轨道倾角的依赖性。将Ａａｒｓｅｔｈ的标准Ｎ体模拟程序加上动力摩擦,形成一个研究星系并合的Ｎ体模拟程序,用来研究小星系群中星系的自旋和轨道倾角的依赖性．结果表明,在小星系群中,的确存在着类似在涡星系中的自旋和轨道倾角的反相关性． 相似文献