共查询到20条相似文献,搜索用时 562 毫秒
1.
传统的哈勃星系形态分类法可以很好地对近邻的亮星系进行分类,但对低面亮度星系、矮椭球星系、矮旋涡星系以及高红移星系等都已无能为力。德沃古勒分类系统、叶凯士分类系统和范登伯分类系统是在哈勃分类法的基础上进行了发展和细化,利用光的中心聚集度或光度级等作为星系形态分类的参数。模型化分类系统试图定量地测量星系形态参数,但需要假定星系面亮度分布满足一定的形式,如r~(1/4)律、指数律等。最近几年,又有一些学者提出了非模型化分类系统,给出了若干个可以直接测量星系形态的结构参数,如:聚集度指数C、非对称指数A、簇聚指数S、基尼系数G及矩指数M_(20)。这些参数可以反映星系的形成历史、恒星形成、与其他星系的相互作用、已经发生或正在进行的并合活动等。它们不仅可以有效地给出近邻星系的分类特性,还能用于测量高红移星系的形态。该文介绍了不同的星系形态分类方法,比较了各类方法的优点和不足。在此基础上,最后介绍了基于非模型化分类系统的星系形态分类的研究进展。 相似文献
2.
通过利用CANDELS-EGS(Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey-Extended Groth Strip)场中HST WFC3(Hubble Space Telescope Wide Field Camera 3)F160W高分辨率的观测图像,研究了9个光谱红极亮红外星系的形态结构特征.发现这些星系的形态表现出多样性(从椭圆到多个亮核或弥散的结构),如:双核,气体桥,双不对称体,不规则或椭圆结构.为了定量地研究这些极亮红外星系的形态,测量了它们在静止光学波段的形态参数(基尼系数G和矩指数M20).与近邻极亮红外星系相比,高红移极亮红外星系的G偏小而M20偏大,表明这些星系的星族分布聚集度小且不对称性大.基于对样本中极亮红外星系2维面亮度轮廓的拟合,得到这些星系的有效半径分布在2.4 kpc到5.8 kpc之间,其平均值是(3.9±1.1)kpc.相比较于近邻相似质量的恒星形成星系来说,高红移极亮红外星系的平均大小要小1到2倍.在类似红移和红外光度条件下,得出的这些结果也与其它文献中给出的结论相一致. 相似文献
3.
为了研究ROSAT X射线选亮近类星体巡天的选择判据,从1995年4月至1996年10月期间,利用北京天台2.16米望远镜进行了试验观测,发现了73个类星体,27个赛弗特星系,1个BL Lac侯选体,1个白矮星和1个激变变星。 相似文献
4.
在“等级式成团”(hierarchical clustering)宇宙学演化框架下,早型星系(E/SO)的形成和演化不是如经典的“整体塌缩”(monolithic collapse)演化模式所描述的是由高红移处的短时间剧烈恒星形成过程一次性完成的;相反,它们可能是在大尺度结构形成过程中由盘星系间的相互合并演化而来,特别是对于质量相当的盘星系间的剧烈合并过程。目前的数值模拟和高分辨成像观测都已证实了这种可能性,而且红移巡天的结果也更多地支持这种演化模式。在此提出一个星系合并过程中核区星暴和中心黑洞共生演化的模型,来解释由空间望远镜(HST)和地面CCD高分辨测光所得的早型星系“黑洞/核球”统计线性相关,也即中心黑洞质量约为其核球体质量的0.6%;同时,该演化模型还可以进一步合理地解释在类星体的近红外成像观测中统计得出的相似的线性相关性,即类星体中心亮度与其母星系质量成正比。并给出此模型计算的极限情况和模型的解析估计。 相似文献
5.
6.
7.
8.
作者认为,有五种误差会影响LAMOST工程光纤定位:(1)光纤的机械定位误差;(2)输入星表与导星星表的误差;(3)焦面坐标系与理想坐标系的转换误差;(4)较差大气折射对观测目标的影响;(5)导星的跟踪误差。并提出在LAMOST工程中有关天体测量的三个研究课题:(1)星表系统差的研究,以提供适合LAMOST使用的导星星表和输入星表;(2)望远镜光学系统畸变的研究以及焦面坐标与理想坐标间关系的确定,提出用国内外观测资料,建立5°×5°的几个标准天区;(3)从现有的光学图象和测光资料中给出LAMOST输入星表中星象的类别,如双星、聚星、变星、星系等。建议LAMOST工程中采用GSC-Ⅱ作为导星星表,而输入星表的精度应好于0.54”。 相似文献
9.
“下一代大型空间天文望远镜”(NGST)、“空间干涉测量飞行任务”(SIM)和“天体物理的全天球天体测量干涉仪”(GAIA)是21世纪初的大型空间天文望远镜的计划。NGST和SIM是NASA“起源计划”的关键项目,可用于探索宇宙最早期形成的第一批星系,星团,NGST是大孔径被动控制冷望远镜,口径4-8m,是哈毂空间望远镜(HST)和红外空间望远镜(SIRTF)的后续项目,它强大的观测能力特别体现在 相似文献
10.
使用澳大利亚致密阵(ATCA)在1.4GHz上观测一个极 度的IRAS星系样本。在这个样本所包括的37个IRAS星系中,探测到19个源的射 电发射 ,获得了它们的射电参数,如峰值位置,射电流量等。该样本的射电功率范围在22.9〈logP1.4G(W/Hz)〈23.8,本文给出了观测的初步结果。 相似文献
11.
We report on the statistical analysis of a sample of AGNs (Seyferts and LINERs) selected from an RBSC-NVSS sample of the brightest X-ray sources. The sample is large enough and unbiased for a detailed study of multi-frequency (radio to X-ray) properties of AGN. There are no significant differences in X-ray, optical, far-infrared, and radio powers, core dominance, radio loudness, radio spectral index, and two-point radio-to-optical and optical-to-X-ray spectral indices of Seyfert types 1 and 2. These findings strongly support the unification model, and the observed differences between Sy1 and Sy2 are due to both the variable obscuration and different geometric orientation effects. The correlation between the X-ray and radio emission over many decades is primary and indicates the intrinsically similar origin of both radiations in Seyfert galaxies, powered mainly by AGN, rather than compact starbursts. For Seyfert galaxies we found that the slopes of the relations L
X - L
R and L
X - L
B are flat, which indicate the existence of components unrelated with X-ray. Perhaps only for LINERs is the observed L
X - L
R relation completely due to AGNs. The Sy1, Sy2, and LINER galaxies show different slopes in the relation L
X - L
1.4, and the relative contribution of extended radio components may be the cause of these differences. The possible effects of unresolved extended radio and X-ray components are quantitatively discussed. 相似文献
12.
The results of the spectroscopic observation of 23 galaxies with a UV excess from Kazarian's lists are presented. The spectra were obtained on the 2.6-m telescope of Byurakan Observatory with a Byu FOSC-2 camera. Two grisms, red and green, were used in the observations. Emission lines are observed in the spectra of 21 of the galaxies. 相似文献
13.
The results of spectroscopic observations of 28 galaxies of the Second Byurakan Sky Survey, completing the follow-up spectroscopy of galaxies in the survey field with central coordinates = 12h22m, = +35°, are presented. The spectra were obtained on the 2.6 m telescope of the Byurakan Astrophysical Observatory, National Academy of Sciences of the Republic of Armenia, and the 6 m telescope of the Special Astrophysical Observatory, Russian Academy of Sciences. The redshifts and absolute stellar magnitudes of all the galaxies have been determined. A preliminary analysis of the spatial distribution of all galaxies in this sample is given. 相似文献
14.
The surroundings of 75 active SB galaxies are investigated. It is shown with a fairly high degree of certainty that more galaxies are observed in the direction of the bar than in other directions. It is concluded that this may be a consequence of the galaxy-forming activity of these galaxies. It is noted that the influence of the surroundings on a galaxy is traditionally discussed, although there is much evidence that the surroundings of a galaxy are shaped due to its activity. 相似文献
15.
16.
Data from the H I Parkes All-Sky Survey (HIPASS) of the southern sky in the neutral hydrogen line are used to determine the radial velocities and widths of the H I line for flat spiral galaxies of the Revised Flat-Galaxy Catalog (RFGC) seen edge-on. The sample of 103 flat galaxies detected in HIPASS is characterized by a median radial velocity of +2037 km/sec and a median width of the H I line at the level of 50% of maximum of 242 km/sec. For RFGC galaxies the 50% detection level in HIPASS corresponds to an apparent magnitude B
t = 14
m
.5 or an angular diameter a = 2.9. The relative number of detected galaxies increases from 2% for the morphological types Sbc and Sc to 41% for the type Sm. The median value of the ratio of hydrogen mass to total mass for RFGC galaxies is 0.079. With allowance for the average internal extinction for edge-on galaxies, <B
t< = 0
m
.75, the median ratio of hydrogen mass to luminosity, M
H I/L
B = 0.74 M
/L
, is typical for late-type spirals. Because of its small depth, HIPASS reveals only a few RFGC galaxies with previously unknown velocities and line widths. 相似文献
17.
A sample of galaxy groups is investigated for the occurence of Seyfert objects within them. The velocity dispersion in groups with Seyfert galaxies is significantly larger than in groups without Seyfert galaxies. But there was not found any correlation between the galaxy density within the groups and the content of Seyfert galaxies. 相似文献
18.
H.M. Tovmassian 《Astronomische Nachrichten》2001,322(2):87-91
It is shown that the samples of Seyfert galaxies used to study different parameters of Seyferts are largely incomplete. The way of estimation of the number of the missed, not detected Seyferts is proposed. It is based on the assumption that distribution of inclinations of Seyferts should be similar to that of spiral galaxies. Addition of the estimated number of the missed Seyferts allows to deduce more correct value of the ratio of numbers of Sy2s to Sy1s, N2/N1. The more real value of the ratio N2/N1 is the one deduced by using the results of counts of bright, nearby Seyferts, and is equal to ∼4. The opening angle of the dust torus is ∼76°. 相似文献
19.
In this paper we present the H map, the 2D velocity field and the rotation curve of the galaxy NGC 784 obtained with the ByuFOSC2 scanning Fabry-Perot interferometer, attached at the prime focus of the 2.6-m telescope of Byurakan Observatory. The H image shows several HII condensations along the major axis of the galaxy. The galaxy has an asymmetric distribution of the H emission. The rotation curve is quite symmetric with a low gradient in the central part of the galaxy. 相似文献
20.
The relevance of interaction to the presence of Seyfert or starburst activity in the nuclei of galaxies is examined. We focus the attention on the close environments of spectroscopically selected samples of Seyfert-1, Seyfert-2 and starburst galaxies. In particular the results of a statistical procedure aimed at finding physical pairs are tested with redshift measurements of the identified pairs. Seyfert and starburts galaxies show an excess of physical companions compared to normal galaxies. This excess tends to increase as one moves from Seyfert to starburst galaxies. 相似文献