Extremes of the Cosmic Web

My research is largely focused on the extremes of the cosmic web of matter. This mesh-like structure evolves over billions of years, seeded by intial small variations in the density of the Universe. I study how over- and under-densities on the largest scales evolve across cosmic history. This work involves studying the statistical properties of clusters and voids in the distribution of galaxies during the last few billion years of the history of the Universe. Also, I investigate the statistical properties of the first galaxies formed in the Universe around 500 million years after the Big Bang, and how their light helped re-ionize the large amounts of hydrogen gas present in the early Universe. 

The statistical properties of these extremes of the cosmic web are highly sensitive to e.g. the properties of dark energy and dark matter, the behaviour of gravity in untested regimes, the masses of neutrinos, as well as galaxy and cluster astrophysics.

I develop and perform measurements of this and other physics, using observations of the extremes of the cosmic web. For this, I am a member of the 4MOST Cosmology and Cluster surveys, the Euclid Consortium Theory Working Group and Primeval Universe Working Groups, the Square Kilometer Array Cosmology and Epoch of Reionization Working Groups, the XMM Cluster Survey, and the XXL Survey. I am an external collaborator in the Dark Energy Survey.

Recent work includes the demonstration of the power of clusters and voids as probes of deviations from General Relativitythe first cosmological parameter estimation based on voidsdiscovery of a powerful new test of modified gravity theories, and the first direct measurement of the statistics of the matter distribution when the Universe was less than 1 billion years old (soon to appear!).