Protogalactic Disks: A New Window on Galaxy Formation

天文学家试图了解星系是如何形成和演化的。巨大的物质丝在重力作用下聚合成星系。然而，人们对这种合并的确切性质知之甚少。最近对正在形成的星系的发现，即所谓的原星系盘，可能会提供关键的缺失信息。这个项目将利用最先进的观测技术对其中的数十个进行系统的调查。这样的观测将同时获得图像和光谱(精确、定量的颜色)。这些数据将首次探测形成星系的物理条件。研究人员将通过公开演讲和协调的社交媒体活动向广大观众传播他们的结果。有两种相互竞争的模型将气体聚合成星系盘：在热吸积模型中，星系间气体落入光晕并受到数百万度的冲击。或者，在冷吸积模型中，这种气体落入光晕时的温度相对较低，约为10,000度。这项提议试图通过对原星系盘的调查来区分这两种模型。马丁和他的合作者之前已经研究了这样一个大小约100kpc的原始星系盘，并通过气丝连接到宇宙网，并发现了冷吸积的证据。该系统受到附近类星体的照射，因此适用于莱曼-阿尔法和其他谱线的2D光谱。这些令人兴奋的观察结果现在正在由其他团队进行研究。只有在最近的仪器设备下，这样的研究才变得可行。在这项提议中，研究人员试图通过使用Palomar宇宙网络成像仪(PCWI)和凯克宇宙网络成像仪(KCWI)的积分场光谱对原星系盘进行系统调查来扩大他们的样本。这些仪器非常适合于这种类型的调查，而本提案的PI是KCWI仪器的PI。一项初步的初步调查显示，在全样本中有许多值得研究的目标。

Astronomers seek to understand how galaxies formed and evolve. Vast filaments of matter coalesce into galaxies under gravity. However, the exact nature of this coalescence is poorly understood. Recent discoveries of galaxies in the process of forming, called proto-galactic disks, may provide key missing information. This project will undertake a systematic survey of dozens of them using state-of-the-art observations. Such observations will obtain both images and spectroscopy (precise, quantitative colors) simultaneously. These data will probe the physical conditions of galaxies-in-formation for the first time. The investigators will disseminate their results to a broad audience through public lectures and a coordinated social media campaign.There are two competing models for coalescing gas into galactic disks: In the hot accretion model, intergalactic gas falls into halos and is shocked to many millions of degrees. Alternatively, in the cold accretion model, this gas falls into halos at a relatively "cold" temperature of ~10,000s of degrees. This proposal seeks to discriminate between these two models by undertaking a survey of proto-galactic disks. Martin and collaborators have previously studied such a proto-galactic disk, ~100 kpc in size, and linked to the cosmic web by a gas filament, and found evidence of cold accretion. The system is illuminated by a nearby quasar, and therefore amenable to 2D spectroscopy in Lyman-alpha and other spectral lines. These exciting observations are now being pursued by other teams. Only with recent instrumentation have such studies become feasible. In this proposal, the investigators seek to expand their sample by conducting a systematic survey of proto-galactic disks using integral field spectroscopy with the Palomar Cosmic Web Imager (PCWI) and the Keck Cosmic Web Imager (KCWI). These instruments are ideally suited to this type of investigation, and the PI of this proposal is the PI of the KCWI instrument. A preliminary pilot survey shows a promising number of targets for study in their full sample.