When Did Quiescent Galaxies First Appear and What Quenched Their Star-Formation?

星系是恒星、气体、尘埃和暗物质的巨大集合，大小、形状和颜色各不相同。了解不同类型的星系是如何形成的是天体物理学的主要任务之一。今天，在当地的宇宙中，最大和最重的星系被发现是静止的（即，不形成新的恒星），由非常古老的恒星组成，典型的年龄为120亿年。为了了解这些附近的星系是如何形成的，我们还需要研究遥远的年轻宇宙中的星系。Marchesini博士和他的团队将使用最高质量的天文观测来研究超过95%的宇宙历史中的静止星系。这些发现将与理论预测进行比较，为在星系形成的早期是什么阻止了恒星的形成提供新的线索。除了培训研究生和本科生外，Marchesini博士还将为高中生实施暑期研究计划，为K-12科学教师的专业发展做出贡献，并发表公开演讲。该项目包括利用哈勃前沿场、地面望远镜（Keck和VLT）和斯皮策- irac的数据构建星系的多波长光度目录。探测到的星系的光谱能量分布将被建模，以得出光度红移和恒星群特性。将测量自红移z=7以来星系的恒星质量函数的演化，特别强调静止星系群。

Galaxies are vast collections of stars, gas, dust, and dark matter, and come in various sizes, shapes, and colors. Understanding how the different types of galaxies formed is one of the major quests in astrophysics. Today, the biggest and heaviest galaxies in the local universe are found to be quiescent (i.e., not forming new stars) and made of very old stars, with typical ages of 12 billion years. To understand how these nearby galaxies formed, their counterparts in the distant, young universe need to be studied as well. Dr. Marchesini and his team will investigate quiescent galaxies over 95% of cosmic history using the highest quality astronomical observations. The findings will be compared with theoretical predictions, providing new clues on what switches off star formation in the early phase of galaxy formation. Besides training graduate and undergraduate students, Dr. Marchesini will implement a summer research program for high-school students, contribute to the professional development of K-12 science teachers, and deliver public lectures. The project includes construction of multi-wavelength photometric catalogs of galaxies using data from the Hubble Frontier Fields, ground-based telescopes (Keck and VLT), and Spitzer-IRAC. The spectral energy distributions of the detected galaxies will be modeled to derive photometric redshifts and stellar population properties. The evolution of the stellar mass function of galaxies since redshift z=7 will be measured, with particular emphasis on the quiescent galaxy population.