Protogalactic Disks: A New Window on Galaxy Formation

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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.