When did galaxies start forming stars? What is the role of distant galaxies in galaxy formation models and the epoch of reionization? What are the conditions in typical star-forming galaxies at redshifts ≳4? Why is galaxy evolution dependent on environment? The Spitzer Space Telescope has been a crucial tool for addressing these questions. Accurate knowledge of stellar masses, ages and star formation rates requires measuring rest-frame optical (and ultraviolet) light, which only Spitzer can probe at high redshifts for a sufficiently large sample of typical galaxies. Many of these science goals are the main science drivers for the James Webb Space Telescope, and Spitzer afforded us their first exploration.

星系何时开始形成恒星？遥远星系在星系形成模型和电离时代中起什么作用？典型的恒星形成星系在红移≳4时的条件是什么？为什么银河系进化取决于环境？Spitzer太空望远镜一直是解决这些问题的重要工具。要准确了解恒星质量，年龄和恒星形成率，需要测量静止帧的光学（和紫外线）光，只有Spitzer才能以足够高的红移探测足够大的典型星系样本。其中许多科学目标是詹姆斯·韦伯（James Webb）太空望远镜的主要科学驱动力，斯皮策（Spitzer）为我们提供了首次探索。