The host galaxies of active galactic nuclei   总被引：2，自引：0，他引：2  

Guinevere Kauffmann  Timothy M. Heckman  Christy Tremonti  Jarle Brinchmann  Stéphane Charlot  Simon D. M. White  Susan E. Ridgway  Jon Brinkmann  Masataka Fukugita  Patrick B. Hall  &#;eljko Ivezi&#;  Gordon T. Richards  Donald P. Schneider 《Monthly notices of the Royal Astronomical Society》2003,346(4):1055-1077

We examine the properties of the host galaxies of 22 623 narrow-line active galactic nuclei (AGN) with  0.02 < z < 0.3  selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O  iii ]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L [O  iii ]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early types. The hosts of high-luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high-luminosity AGN have strong Hδ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O  iii ] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O  iii ] luminosities.  相似文献   

'Hyper-parameters' approach to joint estimation: applications to Cepheid-calibrated distances and X-ray clusters     

Pirin Erdogdu  Stefano Ettori  Ofer Lahav 《Monthly notices of the Royal Astronomical Society》2003,340(2):573-579

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宁远保安地区基性─超基性火山岩基本特征     

陈必河 《湖南地质》1994,(4)

本文论述了保安地区火山岩的地质、岩石、副矿物、岩石化学、微量元素、稀土元素、稳定同位素、火山岩相及火山机构等特征。并对其演化规律、形成机制与成矿作用的关系，作了初步探讨。  相似文献   

陕西关中古代天文遗存     

刘次远  张铭洽 《时间频率学报》1992,15(2):111-120

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强势语下的无奈——辜鸿铭古籍英译的归化     

张小波 《广东海洋大学学报》2004,24(5):70-74

通过对辜鸿铭所翻译的《中庸》、《论语》进行分析和研究 ,反映出社会背景对中国古典文化经典翻译的不同策略的影响。从而证明辜鸿铭译文的别出心裁出于强势语下的无奈。从翻译理论上揭示归化翻译的历史意义以及译品存在的价值。  相似文献   

The maximum stellar mass, star-cluster formation and composite stellar populations     

Carsten Weidner  Pavel Kroupa 《Monthly notices of the Royal Astronomical Society》2006,365(4):1333-1347

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Automated Separation of Stars and Normal Galaxies Based on Statistical Mixture Modeling with RBF Neural Networks     

Dong-Mei Qin  Ping Guo  Zhan-Yi Hu  Yong-Heng ZhaoNational Laboratory of Pattern Recognition Laboratory  Institute of Automation  Chinese Academy of Sciences  Beijing  dmqin@nlpr.ia.ac.cnDepartment of Computer Sciences  Beijing Normal University  Beijing National Astronomical Observatories  Chinese Academy of Sciences  Beijing 《中国天文和天体物理学报》2003,3(3)

For LAMOST, the largest sky survey program in China, the solution of the problem of automatic discrimination of stars from galaxies by spectra has shown that the results of the PSF test can be significantly refined. However, the problem is made worse when the redshifts of galaxies are not available. We present a new automatic method of star/(normal) galaxy separation, which is based on Statistical Mixture Modeling with Radial Basis Function Neural Networks (SMM-RBFNN). This work is a continuation of our previous one, where active and non-active celestial objects were successfully segregated. By combining the method in this paper and the previous one, stars can now be effectively separated from galaxies and AGNs by their spectra-a major goal of LAMOST, and an indispensable step in any automatic spectrum classification system. In our work, the training set includes standard stellar spectra from Jacoby's spectrum library and simulated galaxy spectra of EO, SO, Sa, Sb types with redshift ranging from 0 to 1  相似文献   

Cosmological constraints from Chandra X-ray observations of galaxy clusters     

S.W. Allen 《Astrophysics and Space Science》2003,285(1):247-256

Chandra X-ray observations of rich, dynamically relaxed galaxy clusters allow the properties of the X-ray gas and the total gravitating mass to be determined precisely. Here, we discuss how Chandra observations may be used as a powerful tool for cosmological studies. By combining Chandra X-ray results on the X-ray gas mass fractions in clusters with independent measurements of the Hubble constant and the mean baryonic matter density of the universe, we obtain a tight constraint on the mean total matter density of the universe, Ο_m, and an interesting constraint on the cosmological constant, Ο_Λ. Using these results, together with the observed local X-ray luminosity function of the most X-ray luminous galaxy clusters, a mass-luminosity relation determined from Chandra and ROSAT X-ray data and weak gravitational lensing observations, and the mass function predicted by numerical simulations, we obtain a precise constraint on the normalization of the power spectrum of density fluctuations in the nearby universe,σ₈. We compare our results with those obtained from other, independent methods. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Hα Photometry of Two Contact Binaries     

Szilárd Csizmadia  Zsolt Kővári  Péter Klagyivik 《Astrophysics and Space Science》2006,304(1-4):355-357

We carried out optical and Hα photometry of two contact binaries (V861 Herculis, EQ Tauri). The light curve modeling revealed stellar spots in both contact systems and strong Hα excess in the position of the observed stellar spots. A correlation was found between the V−R and R−H_α colour indices of V861 Her.  相似文献   

Galaxy voids in cold dark matter universes     

A. J. Benson  Fiona Hoyle  Fernando Torres  Michael S. Vogeley 《Monthly notices of the Royal Astronomical Society》2003,340(1):160-174

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