标题： 哈勃深场-南的星系数量和大小：下一代空间望远镜的启示 显示英文标题

标题： Counts and Sizes of Galaxies in the Hubble Deep Field - South: Implications for the Next Generation Space Telescope

摘要： 下一代空间望远镜（NGST）的科学目标包括大量的星系巡天，既有成像也有光谱学。 哈勃深场数据集包括了有史以来在紫外、光学和近红外波段所做的最深观测，其深度与预期的NGST光谱观测相当。 我们展示了哈勃深场南区（HDF-South）图像的源计数、星系大小和等亮度线填充因子。 观测到的积分星系计数在AB<30时每平方角分超过500个星系。 我们通过模型将这些计数扩展到了红外中的暗弱星系。 先前观察到的更暗弱的星系较小的趋势，在高分辨率的HDF-S STIS图像中持续到AB=29，其中星系的半光度半径通常为0.1角秒。 广泛的蒙特卡洛模拟显示，测量到的小尺寸并非由于选择效应，直到>29星等才受到影响。 利用HDF-S NICMOS图像，我们表明星系在近红外波段比在光学波段更小。 我们分析了HDF-S STIS图像的等亮度线填充因子，并表明即使在星系探测极限下，该图像也主要是空旷的天空，我们预计这一结论对于NGST光谱观测同样适用。 然而，在NGST成像预期的面亮度极限下，大约四分之一的天空被AB<30星等的星系外等亮度线占据。 我们讨论了这些数据对NGST近红外光谱仪几种设计概念的影响。 我们比较了各种设计的分辨率和混淆限制效应，以及多目标或多场光谱的多重优势。 我们认为，对于高红移星系的NGST光谱观测，最优的选择是一种多目标光谱仪（MOS），通过微机电系统（MEMS）设备进行目标选择。 显示英文摘要

摘要： Science objectives for the Next Generation Space Telescope (NGST) include a large component of galaxy surveys, both imaging and spectroscopy. The Hubble Deep Field datasets include the deepest observations ever made in the ultraviolet, optical and near infrared, reaching depths comparable to that expected for NGST spectroscopy. We present the source counts, galaxy sizes and isophotal filling factors of the HDF-South images. The observed integrated galaxy counts reach >500 galaxies per square arcminute at AB<30. We extend these counts to faint levels in the infrared using models. The trend previously seen that fainter galaxies are smaller, continues to AB=29 in the high resolution HDF-S STIS image, where galaxies have a typical half-light radius of 0.1 arcseconds. Extensive Monte Carlo simulations show that the small measured sizes are not due to selection effects until >29mag. Using the HDF-S NICMOS image, we show that galaxies are smaller in the near infrared than they are in the optical. We analyze the isophotal filling factor of the HDF-S STIS image, and show that this image is mostly empty sky even at the limits of galaxy detection, a conclusion we expect to hold true for NGST spectroscopy. At the surface brightness limits expected for NGST imaging, however, about a quarter of the sky is occupied by the outer isophotes of AB<30 galaxies. We discuss the implications of these data on several design concepts of the NGST near-infrared spectrograph. We compare the effects of resolution and the confusion limit of various designs, as well as the multiplexing advantages of either multi-object or full-field spectroscopy. We argue that the optimal choice for NGST spectroscopy of high redshift galaxies is a multi-object spectrograph (MOS) with target selection by a micro electro mechanical system (MEMS) device.