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。 巨大的物质细丝在引力作用下凝聚成星系。 然而，这种聚结的确切性质知之甚少。 最近发现的星系正在形成过程中，称为原星系盘，可能提供关键的缺失信息。 该项目将利用最先进的观测手段对其中几十个进行系统调查。 这样的观测将同时获得图像和光谱（精确，定量的颜色）。 这些数据将首次探索星系形成的物理条件。 研究人员将通过公开讲座和协调的社交媒体活动向广大受众传播他们的结果。有两种相互竞争的模型将气体聚结成星系盘：在热吸积模型中，星系间气体福尔斯落入晕中，并受到数百万度的冲击。 或者，在冷吸积模型中，这种气体福尔斯在相对“冷”的温度下（约10,000摄氏度）落入晕圈。 这项建议试图通过对原银河系盘进行调查来区分这两种模型。 马丁和他的合作者之前已经研究过这样一个原星系盘，大小约为100千秒差距，通过一个气体细丝与宇宙网相连，并发现了冷吸积的证据。 该系统被附近的类星体照亮，因此可以在莱曼α和其他光谱线上进行2D光谱分析。 这些令人兴奋的观察结果现在正被其他团队所追求。 只有使用最近的仪器，这样的研究才变得可行。 在这项提案中，研究人员试图通过使用Palomar Cosmic Web Imager（PCWI）和Keck Cosmic Web Imager（KCWI）的积分场光谱学对原星系盘进行系统调查来扩大他们的样本。 这些仪器非常适合此类调查，本提案的PI是KCWI仪器的PI。 初步的试点调查显示，在其全部样本中有许多目标值得研究。

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.