Near-Infrared Surveys for High-Redshift Quasars

AST 95-09919 由于类星体的亮度很高，可以在很远的距离上被探测到，也就是说，它们的红移很高。对高红移类星体的调查已经提供了许多新的科学见解。例如，现在很清楚，类星体的密度随着距离的增加（年龄的减小）而迅速上升，在红移2.0和3.5之间的某个地方停止，最近完成的调查提供了证据，类星体的空间密度在更高的红移处下降。此外，金属发射线的强度没有明显的红移变化，这表明类星体的物质已经通过几代恒星的演化而富集，即使是在最大的已知红移下。目前正在进行的其他调查是通过小面积深度无狭缝调查来测量暗类星体的光度函数，并通过两个大面积调查来寻找非常高的红移类星体，使用4.1 z 5.5的CCD图像，以及红移超过6的无狭缝光谱。每次调查都将出版一份目录。 ***

AST 95-09919 Because of their great luminosity, quasars can be detected at enormous distances, i.e. high redshift. Surveys for high redshift quasars have already provided a number of new scientific insights. For example, it is now clear that the rapid rise in the density of quasars with increasing distance (decreasing age) halts somewhere between redshifts 2.0 and 3.5, and a recently completed survey has provided evidence that the space density of quasars declines at higher redshifts. Also, there is no significant change with redshift in the strengths of the metal emission lines, indicating that the quasar material has already been enriched by several generations of stellar evolution even at the largest known redshifts. Other surveys are now being carried out to measure the luminosity function of faint quasars via a small-area deep slitless survey, and to search for very high redshift quasars via two large-area surveys, using multicolor CCD images for 4.1 z 5.5, and with slitless spectra out to redshifts beyond 6. A catalog will be published for each survey. ***