The evolution of galaxies in the early universe with the next generation of telescopes

天文学研究的前沿是对第一个星系的形成和演化的研究。在过去的30年里，通过突破性的观测，我们已经有可能识别出宇宙诞生不到5亿年的星系。与当地的宇宙相比，这些星系具有不同寻常的特性，表现出低化学富集和尘埃遮挡，以及不规则的形态。迄今为止，对早期星系的大多数研究都集中在那个时代的“典型”星系上，使用深铅笔束哈勃太空望远镜进行观测。这些低质量、常见的高红移源已经被很好地研究过了，但是对高质量的源还缺乏了解。这个项目的重点是利用目前最好的数据集来了解这些明亮的、高质量的星系。正是这些罕见而明亮的来源，被认为是早期宇宙中最早的化学富集和尘埃产生的地方。此外，据预测，它们可以精确定位密度最高的环境。在z = 7处，在再电离时期，人们认为密度最高的区域也将是电离程度最高的区域，因为中心星系和相关/卫星星系都会产生电离光子，从而在中性的星系间介质中产生气泡。最后，仅仅是最大质量源的数量密度就提供了星系演化的关键限制，因为这些源是最难在模拟中产生的。AGN反馈的作用、合并和低金属丰度环境下的恒星形成效率都可能对高SFR或大质量星系能否在第一个十亿年内存在产生重大影响。该项目旨在利用目前最好的广域数据集来发现和研究高红移星系。在项目结束时，学生将使用来自维拉鲁宾天文台（VRO）和欧几里得太空任务的第一批数据来扩展这项研究，如果他们选择这项研究，将为他们未来的研究提供一个极好的位置。该项目的目标是了解宇宙中大多数恒星形成星系的时间和方式。该学生将成为多波段光度法选择高红移星系的专家。然后，他们将使用得到的样本来约束这些光源的数量密度的演变（通过光度函数）。为了理解天体物理学，这些导出的光度函数将与一系列宇宙学星系演化模型进行比较。博士学位可以分为3-4个项目，所有项目都应该有论文发表。在第一个项目中，学生将分析最佳的基于地面的广域调查，以搜索z = 7星系。在使用视频调查之前，没有人这样做过。具体来说，他们将在XMM-LSS和CDFS领域将斯巴鲁super - prime Cam光学成像与视频数据进行像素匹配。他们将从这些图像中生成目录，并进行强大的光谱-能量分布拟合分析，以搜索z = 7的候选者。然后将仔细检查候选人，以去除任何人工制品或污染物（例如褐矮星）。一旦最终样品被定义，学生将在这些红移处计算静帧紫外光度函数，将其扩展到非常明亮的绝对星等。这种研究方法将以该领域以前的经验为基础。光度函数的分析将采用一种新的方法，不使用分形（核密度估计）。这将导致一个强有力的第一作者发表。对于接下来的2-3个项目，根据学生的偏好，有几个选择，这取决于这个领域的状态。我在下面简要地概述了不同的项目。1)对高红移样本进行聚类分析，以确定可能的晕质量，并研究恒星形成效率的函数

At the cutting-edge of Astronomy research is the study of the formation and evolution of the first galaxies. Through breakthrough observations in the past 30 years it has been possible to identify galaxies from when the universe was less than 500 million years old. These galaxies have unusual properties compared to the local universe, showing low chemical enrichment and dust obscuration, and irregular morphologies. The majority of studies of early galaxies to date have focused on 'typical' galaxies at that epoch, using deep pencil beam Hubble Space Telescope observations. These low mass, common high-redshift sources have been well studied however there is a lack of knowledge about the high mass end of the population. This project focuses on exploiting the current best datasets for understanding these bright, high mass galaxies. It is these rare and bright sources that are expected to be the sites of the earliest chemical enrichment and dust production in the early Universe. Furthermore, they are predicted to pinpoint the highest density environments. At z = 7, within the Epoch of Reionization, it is thought that the highest density regions will also be the most ionized, as both the central and associated/satellite galaxies produce ionizing photons that generate bubbles in the otherwise neutral Inter-galactic medium. Finally, simply the number density of the most massive sources provides key constraints on galaxy evolution, as it is these sources that are the hardest to produce in simulations. The role of AGN feedback, mergers and the star-formation efficiency in low-metallicity environments could all have a large impact on whether high SFR or mass galaxies can exist in the first billion years. Aims and objectivesThis project aims to exploit the current best wide-area datasets to find and study galaxies at high-redshift. At the end of the project the student will use the first data from the Vera Rubin Observatory (VRO) and Euclid space-mission to extend this research, putting them in an excellent position for future research if they choose this. The goal of the project is to understand when and how the most star-forming galaxies formed in the Universe. The student will become an expert in the selection of high-redshift galaxies from multi-band photometry. They will then use the resulting samples to constrain the evolution of the number density of these sources (via the luminosity function). To understand the astrophysics, these derived luminosity functions will be compared with a range of cosmological galaxy evolution models.The PhD can be split into 3-4 projects, all of which should lead to publications. In the first project the student will analyse the best available ground-based wide area surveys to search for z = 7 galaxies. This has not been done before using the VIDEO survey. Specificially they will pixel match the Subaru Hyper-Suprime Cam optical imaging to the VIDEO data in the XMM-LSS and CDFS fields. They will produce catalogues from these images, and do a robust Spectral-Energy Distribution fitting analysis to search for z = 7 candidates. The candidates will then be carefully inspected to remove any artefacts or contaminants (e.g. brown dwarfs). Once a final sample has been defined the student will compute the rest-frame UV luminosity function at these redshifts, extending this to very bright absolute magnitudes. The research method will build upon previous experience in the field. The luminosity functions will be analysed with a novel method that does not use binning (kernel density estimator). This will result in a strong first author publication. For the next 2-3 projects there are several options depending on the state of the field at this point, guided by the student's preference. I outline briefly the different projects below.1) Clustering analysis of high-redshift samples, to determine the likely halo masses and to study the star-formation efficiency as a function