Infrared Galaxies in the Nearby Universe

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%.     

Classification of extremely red objects in the Hubble Ultra Deep Field

We present a quantitative study of the classification of Extremely Red Objects (EROs). The analysis is based on the multi-band spatial-and ground-based observa-tions (HST/ACS-BViz, HST/NICMOS-JH, VLT-JHK) in the Hubble Ultra Deep Field (UDF). Over a total sky area of 5.50 arcmin2 in the UDF, we select 24 EROs with the color criterion (i-K)vega 3.9, corresponding to (I-K)vega 4.0, down to KVega = 22. We develop four methods to classify EROs into Old passively evolving Galaxies (OGs) and Dusty star-forming Galaxies (DGs), including (i-K) vs. (J-K) color diagram,spectral energy distribution fitting method, Spitzer MIPS 24μm image matching, and nonparametric measure of galaxy morphology, and found that the classification results from these methods agree well. Using these four classification methods, we classify our EROs sample into 60Gs and 8 DGs to KVega < 20.5, and 80Gs and 16 DGs to KVega < 22, respectively. The fraction of DGs increases from 8/14 at KVega < 20.5to 16/24 at Kvega < 22. To study the morphology of galaxies with its wavelength, we measure the central concentration and the Gini coefficient for the 24 EROs in our sample in HST/ACS-i, z and HST/NICMOS-J, H bands. We find that the morphological param-eters of galaxies in our sample depend on the wavelength of observation, which suggests that caution is necessary when comparing single wavelength band images of galaxies at a variety of redshifts.     

星族合成方法及发射线星系核区中的恒星组分

论述星族合成方法对研究复合恒星体系的重要意义。综述了星族合成的三种基本方法，着重介绍了以星团光谱为样本的星族合成方法及其应用，最后，作为一个例子，我们利用ＣＳＰＳ方法给出发射线星系Ｍｒｋ４９９谱的合成结果。     

星系团的光学研究（Ⅱ）：团星系演化,环境与形态,简要的展望

星系团研究涉及面极广，此处仅简介光学研究的若干方面，全文分为两篇，前一篇中已知介绍了星系团表，星系团有大尺度分布，星系团的一般性质，本篇中则介绍团星系的演化，环境与星系形态，并作简要的展望。     

星族合成

以简单星族为例介绍了演化星族合成的算法 ,并总结了在演化星族合成中常用的恒星演化库 ,光谱库 ,初始质量函数和合成判据 ,最后简要讨论了目前星族合成中仍存在的问题。     

Low-redshift Galaxies in the Infrared and Submillimetre

In recent years the evolution of dust-enshrouded galaxies has become an important issue in cosmology. We present the results of a study linking the high- and low-redshift populations of such galaxies. Previously, a simple hierarchical clustering model was found to be successful in describing the high-redshift populations of dusty galaxies. This study showed that strong evolution could not be avoided in order to satisfy all the high-redshift infrared and submillimetre constraints. We now apply the same model to the low-redshift data available, and find that the strong evolution inferred is compatible with the count and redshift data we have from IRAS and ISO. This revised version was published online in September 2006 with corrections to the Cover Date.     

The Effect of Method of Constructing the Mass Distribution on Single Stellar Populations

We use two methods of constructing the initial mass distribution, the traditional way and Monte Carlo simulation, to obtain integrated U - B, B - V, V-R and V-I colours and absorption-line indices denned by the Lick Observatory image dissector scanner (referred to as Lick/IDS), for instantaneous burst solarmetallicity single stellar populations with ages in the range 1-15 Gyr. We find that the evolutionary curves of all colours obtained by the traditional method are smoother than those by Monte Carlo simulation, that the U - B and B - V colours obtained by the two methods agree with one another, while the V - R and V - I colours by the traditional method are bluer than those by Monte Carlo simulation. A comparison of the Lick/IDS absorption-line indices shows that the variations in all the indices by the traditional method are smoother than that for the Monte Carlo simulation, and that all the indices except for TiO1 and TiO2 are consistent with those for the Monte Carlo simulation.     

Galaxy formation in the reionization epoch as hinted by Wide Field Camera 3 observations of the Hubble Ultra Deep Field

We present a large sample of candidate galaxies at z ≈ 7-10,selected in the Hubble Ultra Deep Field using the new observations of the Wide Field Camera 3that was recently installed on the Hubble Space Telescope.Our sample is composed of 20 z850-dropouts(four new discoveries),15 Y105-dropouts(nine new discoveries)and 20 J125-dropouts(all new discoveries).The surface densities of the z850-dropouts are close to what was predicted by earlier studies,however,those of the Y105-and J125-dropouts are quite unexpected.While no Y105-or J125-dropouts have been found at AB < 28.0 mag,their surface densities seem to increase sharply at fainter levels.While some of these candidates seem to be close to foreground galaxies and thus could possibly be gravitationally lensed,the overall surface densities after excluding such cases are still much higher than what would be expected if the luminosity function does not evolve from z～7 to 10.Motivated by such steep increases,we tentatively propose a set of Schechter function parameters to describe the luminosity functions at z ≈ 8 and 10.As compared to their counterpart at z ≈ 7,here L*decreases by a factor demanded by the existing observations,they are allowed and seem to agree with the data better than other alternatives.If these luminosity functions are still valid beyond our current detection limit,this would imply a sudden emergence of a large number of low-luminosity galaxies when looking back in time to z ≈ 10,which,while seemingly exotic,would naturally fit in the picture of the cosmic hydrogen reionization.These early galaxies could easily account for the ionizing photon budget required by the reionization,and they would imply that the global star formation rate density might start from a very high value at z ≈ 10,rapidly reach the minimum at z ≈ 7,and start to rise again towards z ≈ 6.In this scenario,the majority of the stellar mass that the universe assembled through the reionization epoch seems still undetected by current observations at z ≈ 6.     

Gamma-ray luminosity function of gamma-ray bright AGNs

Detection of γ-ray emissions from a class of active galactic nuclei (viz blazars),has been one of the important findings from the Compton Gamma-Ray Observatory (CGRO). However, their-γ-ray luminosity function has not been well determined. Few at-tempts have been made in earlier works, where BL Lacs and Flat Spectrum Radio Quasars (FSRQs) have been considered as a single source class. In this paper, we investigated the evolution and γ-ray luminosity function of FSRQs and BL Lacs separately. Our investi-gation indicates no evolution for BL Lacs, however FSRQs show significant evolution. Pure luminosity evolution is assumed for FSRQs and exponential and power law evolu-tion models are examined. Due to the small number of sources, the low luminosity end index of the luminosity function for FSRQs is constrained with an upper limit. BL Lac lu-minosity function shows no signature of break. As a consistency check, the model source distributions derived from these luminosity functions show no significant departure from the observed source distributions.