Near-Infrared Surveys for High-Redshift Quasars

AST95-09919由于类星体的光度很大，所以可以在很远的距离上探测到它们，即高红移。对高红移类星体的调查已经提供了一些新的科学见解。例如，现在很明显，类星体密度的快速上升随着距离的增加(年龄的减小)在红移2.0和3.5之间的某个地方停止，最近完成的一项调查提供了证据，表明类星体的空间密度在较高的红移时下降。此外，金属发射线的强度没有明显的红移，这表明即使在已知的最大红移的情况下，类星体材料也已经经过了几代恒星的演化而变得丰富。目前正在进行其他调查，以通过小区域深部无缝隙探测来测量微弱类星体的光度函数，并通过两次大范围调查来寻找极高红移的类星体，使用4.1 z 5.5的多色CCD图像，以及无狭缝光谱到红移超过6的情况。每一次调查都将发布一个目录。***

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. ***