My research focuses on the intergalactic medium (IGM), the "cosmic web" of dark matter and gas that fills deep space.  This filamentary network formed from tiny density fluctuations in the infant Universe.  Over time these structures were amplified by gravity, stretched by cosmic expansion, and changed by the radiation and outflows from galaxies.  My group tries to determine how the IGM evolved over cosmic history as a way of learning about cosmology and galaxy formation.

Because the IGM emits very little light of its own we mainly study it by the way in which it absorbs light from distant objects like quasars.  The figure above shows how the light from a quasar accumulates a series of absorption features as it travels through the IGM.  Most of this absorption is from hydrogen, although trace elements such as oxygen and carbon are also seen.  My group's work is largely based on quasar absorption spectra like this one.  We also study the galaxies along quasar lines of sight to determine how they interact with their intergalactic environments.

My group uses data from large telescopes to infer fundamental properties of the IGM such as its ionization, temperature, and elemental enrichment.  Our goal is determine how these properties change with time and respond to the feedback from galaxies.  We are particulary interested the period of cosmic history known as "reionization" in which ultraviolet radiation from early galaxies ionized nearly every atom in deep space.  We also use quasar spectra to gain insights into the nature of dark matter.