Discovery of a single faint AGN in a large sample of z > 5 Lyman break galaxies

As part of a large spectroscopic survey of   z > 5  Lyman break galaxies (LBGs), we have identified a single source which is clearly hosting an active galactic nucleus (AGN). Out of a sample of more than 50 spectroscopically confirmed R -band dropout galaxies at   z ∼ 5  and above, only J104048.6−115550.2 at   z = 5.44  shows evidence for a high ionization potential emission line indicating the presence of a hard ionizing continuum from an AGN. Like most objects in our sample the rest-frame-UV spectrum shows the UV continuum breaking across a Lyα line. Uniquely within this sample of LBGs, emission from N  v is also detected, a clear signature of AGN photoionization. The object is spatially resolved in Hubble Space Telescope ( HST ) imaging. This, and the comparatively high Lyα/N  v flux ratio indicates that the majority of the Lyα (and the UV continuum longward of it) originates from stellar photoionization, a product of the ongoing starburst in the LBG. Even without the AGN emission, this object would have been photometrically selected and spectroscopically confirmed as a Lyman break in our survey. The measured optical flux  ( I _AB= 26.1)  is therefore an upper limit to that from the AGN and is of order 100 times fainter than the majority of known quasars at these redshifts. The detection of a single object in our survey volume is consistent with the best current models of high redshift AGN luminosity function, providing a substantial fraction of such AGN is found within luminous starbursting galaxies. We discuss the cosmological implications of this discovery.     

Fuzzy概率模型在淮北平原地下水水质评价中的应用

地下水质量正确评价是区域水环境保护的重要前提.依据地下水环境质量分类标准,运用Fuzzy模型对研究区内的地下水质量进行评价.在对区域环境内的各单项污染指标进行分级评价的基础上,考虑到各单项污染指标在总评价中的地位,将各单项污染指标的作用综合起来,建立了Fuzzy概率模型.实例研究结果表明:Fuzzy概率模型可行,原理简明,淮北地区地下水环境的综合质量属于Ⅲ级,从而在整体上可以看出淮北地区地下水的总的污染程度属于中等,符合当地的实际情况.为合理的评价地下水水质和制定污染保护的措施奠定了基础.     

基于J2EE和XML的分布式GIS研究

分布式对象技术和Web Services技术日臻成熟,在IT领域已经广泛使用。在地理信息系统领域,由于空间数据的特点,分布式地理信息系统的理论和实践还有待完善。论文首先分析了相关技术存在的问题,并在此基础上阐述了基于J2EE和XML的分布式GIS体系结构,最后对涉及的关键技术进行了分析。     

分布式环境监测分析WebGIS的设计与实现

实现人类社会的可持续发展必须以客观环境的大力保护为基础,而科学及时的环境监测是人类准确掌握生存环境的变化以制定合理的应对措施,并最终达到环境保护目的。针对现有环境监测站点难以实现实时或准实时的环境监测信息报送及分析的现状,本文基于分布式的地理信息系统平台,设计实现了某省的分布式环境监测网络地理信息系统,服务于环境状况监测信息的分析与发布。     

Optical observations of the Be/X‐ray transient system KS 1947+300

ROTSE‐IIId observations of the Be/X‐ray transient system KS 1947+300 obtained between September 2004 and December 2005 make it possible to study the correlation between optical and X‐ray activity. The optical outburst of 0.1 mag was accompanied by an increase of the X‐ray flux in the 2004 observations. A strong correlation between the optical and X‐ray light curves suggests that the neutron star directly accretes from the outflowing material of the Be star. The nearly zero time lag between X‐ray and optical light curves suggests a heating of the disk of Be star by X‐rays. No optical brightening and X‐ray enhancement was seen in the 2005 observations. There is no indication of an orbital modulation in the optical light curve. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Detection of the optical counterpart of the proposed double degenerate polar RX J1914+24

We have detected the optical counterpart of the proposed double degenerate polar RX J1914+24. The I -band light curve is modulated on the 9.5-min period seen in X-rays. There is no evidence for any other periods. No significant modulation is seen in J . The infrared colours of RX J1914+24 are not consistent with a main-sequence dwarf secondary star. Our ASCA spectrum of RX J1914+24 is typical of a heavily absorbed polar and our ASCA light curve also shows only the 9.5-min period. We find that the folded I band and X-ray light curves are out of phase. We attribute the I -band flux to the irradiated face of the donor star. The long-term X-ray light curve shows a variation in the observed flux of up to an order of magnitude. These observations strengthen the view that RX J1914+24 is indeed the first double degenerate polar to be detected. In this light, we discuss the synchronizing mechanisms in such a close binary and other system parameters.