The field of cosmology has to make do with a theory of structure that is incomplete in the ``ultraviolet'' -- we lack a precise understanding of the cosmologically minute scales on which galaxies form and affect their surroundings. I will review methods to circumvent this limitation, with a particular focus on using the ultra-dilute gas that lies far from galaxies as probed by intergalactic hydrogen absorption. This absorption provides our strongest constraints on the warmness/fuzziness of the dark matter, and it has untapped potential for revealing when the first galaxies formed and ionized the Universe. The standard picture is that, other than the cosmological model, the only other property that matters for shaping this absorption is the gas temperature. Indeed, the temperature is the major impediment for using this absorption to constrain the warmness/fuzziness of the dark matter, and precisely measuring the temperature from this absorption would reveal when the first galaxies formed. I will discuss my group's work to finalize the often elegant rules that shape the temperature of intergalactic gas, as well as these rules' implications for existing measurements. I will conclude provocatively, by questioning the standard picture for intergalactic gas; I will present a preliminary measurement and a research program pursuing further tests of this picture.
Speaker: Matt McQuinn, Washington State Univ.
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