检索结果-南通市图书馆

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

引用

Research in Astronomy and Astrophysics 2010年第9期10卷 867-904页

作者： Hao-Jing Yan Rogier A. Windhorst nimish e hathi Seth H. Cohen Russell e.Ryan Robert W. O＇Connell Patrick J. McCarthy Center for Cosmology and AstroParticle Physics The Ohio State University 191 West Woodruff Avenue Columbus OH 43210 USA School of earth and Space exploration Arizona State University Tempe AZ 85287 USA Department of Physics ＆ Astronomy University of California Riverside CA 92521 USA Department of Physics University of California One Shields Avenue Davis CA 95616 USA Astronomy Department University of Virginia P.O. Box 3818 Charlottesville VA 22903 USA Observatories of the Carnegie Institution of Washington 813 Santa Barbara Street Pasadena CA 91101 USA

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 3 that 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 of ～ 6.5 and Ф^＊ increases by a factor of 17-90. Although such parameters are not yet 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 maj

关键词： cosmology observations -- cosmology early universe -- galaxies evolution -- galaxies luminosity function, mass function -- infrared galaxies

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Fe^(3+)-substitution effect on the thermal variation of J-e characteristics and DC resistivity of quadruple perovskite CaCu_(3)Ti_(4)O_(12)

引用

Journal of Semiconductors 2022年第3期43卷 47-56页

作者： Kunal B.Modi Pooja Y.Raval Dolly J.Parekh Shrey K.Modi Niketa P.Joshi Akshay R.Makadiya nimish H.Vasoya Utpal S.Joshi Department of Physics Saurashtra UniversityRajkot 360005India Department of Physics C.U.Shah UniversityWadhwan CitySurendranagar 363030India Department of environment engineering L.D.Engineering CollegeAhmedabad 380015India Department of Balbhavan Children´s UniversitySector-20Gandhinagar 382015India Department of Physics University School of SciencesGujarat UniversityAhmedabad 380009India

The electrical properties of cubic perovskite series,CaCu_(3-x)Ti_(4-x)Fe_(2x)O_(12)with x=0.0,0.1,0.3,0.5,and 0.7,have been studied by employing current density as a function of electric field characteristics registered at different temperatures and thermal variations of direct current electrical resistivity *** of the compositions exhibit strong non-ohmic *** concentration dependence of breakdown field,the temperature at which switching action takes place,and maximum value of current density(J_(max))has been explained on account of structural,microstructural,and positron lifetime *** highest ever reported value of J_(max)=327 mA/cm^(2)has been observed for pristine *** values of the nonlinear coefficient advise the suitability of ceramics for low-voltage varistor *** Arrhenius plots show typical semiconducting *** activation energy values indicate that electric conduction proceeds through electrons with deformation in the system.

关键词： perovskites magnetic materials J-e characteristics capacitor

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：