Environmental effects at early cosmic times: galaxy evolution in the first massive clusters

本项目是基于最近在2500平方度以上的SPT-SZ巡天中通过Sunyaev-Zeldovich效应探测到的z>~1.4的5个高显著性（S/N>5）星系团的完整样本，利用HST和Spitzer进行的深度均匀成像跟踪。SPT-SZ的大范围调查和深度允许在这个宇宙时代已知的最罕见、最巨大的星团中识别这个仍然独特的星团样本。星团选择与星团质量密切相关，完全独立于星团星系（不像大多数在这些红移的星团调查），使得这个样本非常适合于在早期星团环境中探测星系演化的环境特征的无偏星系种群研究。我们设计了HST和斯皮策观测的特定组合，以提供第一个“基本数据集”，以便开始有效地探测星系群，包括恒星形成和淬火，恒星质量组合，被动部分与恒星质量，红色序列的形成，最亮星团星系的形成和演化，形态与恒星种群特性，鼓状和盘状主导星系的结构演化。在这些极端环境下的合并率和性质，以及星系恒星质量函数、晕的占据分布和大多数大质量晕的恒星质量分数。所有的HST和斯皮策观测现在都已经完成并减少了。第一个分析是由dlr支持的HST观测项目进行的，确认了这些星团的高红移性质，从（完全独立的）红序列和x射线模型分析中，最遥远的系统一致地估计为z~1.8。在这种红移下，它不仅是在SPT-SZ巡天中发现的最遥远的星团，也是迄今为止发现的最遥远的大质量星团（M500 bbb10 ^14 Msun），而且可能是在这种极端质量范围内已知的最遥远的星团，无论选择如何。我们在此请求支持继续这项工作，特别是充分利用HST和斯皮策观测之间的协同作用，这对这项研究的目标至关重要。提议的项目将使我们能够完成对这种定义良好、均匀的大规模遥远星团样本的首次研究，并利用其试点项目的性质，为新的和即将到来的调查（SPTpol, SPT-3G, eROSITA）进行星系演化研究的遥远星团后续有效设计，将当今最先进的工作与其强大的未来扩展连接起来。

This project is based on recently obtained, deep, homogeneous imaging follow-up with HST and Spitzer of the complete sample of five high-significance (S/N>5) galaxy clusters at z>~1.4 detected through the Sunyaev-Zeldovich effect in the SPT-SZ survey over 2500 square degrees. The large survey area and depth of SPT-SZ allow the identification of this still unique sample of clusters among the rarest, most massive known at this cosmic epoch. The cluster selection, tightly related to cluster mass and totally independent of cluster galaxies (unlike most cluster surveys at these redshifts), makes this sample uniquely suited for unbiased galaxy population studies probing environmental signatures on galaxy evolution in early cluster environments. We designed the specific combination of HST and Spitzer observations to provide a first "essential data set" to start efficiently probing galaxy populations in terms of star formation and quenching, stellar mass assembly, passive fractions vs. stellar mass, formation of the red sequence, formation and evolution of Brightest Cluster Galaxies, morphologies vs. stellar population properties, structural evolution of bulge- and disk-dominated galaxies, and merger rates and properties in these extreme environments, as well as the galaxy stellar mass function, halo occupation distribution and stellar mass fraction in most massive halos at z~1.5. All HST and Spitzer observations are now completed and reduced. First analyses are ongoing with a DLR-supported program focused on the HST observations, confirming the high-redshift nature of these clusters, with the most distant system being consistently estimated at z~1.8 from both the (totally independent) red-sequence and X-ray modeling analyses. At this redshift, it is not only the most distant cluster discovered in the SPT-SZ survey, but the most distant massive (M500>10^14 Msun) ICM-selected cluster discovered thus far, and potentially the most distant cluster known in this extreme mass range irrespective of selection. We ask here for support for continuing this work, in particular fully exploiting the synergy between HST and Spitzer observations which is critical to the goals of this investigation.The proposed project will allow us to complete the first study of this kind of such a well defined, homogeneous massive distant cluster sample, and exploit its pilot-project nature for an efficient design of follow-up of distant clusters for galaxy evolution studies for new and coming surveys (SPTpol, SPT-3G, eROSITA), bridging today's state-of-the-art work and its powerful future extensions.