Dark energy: what drives cosmic acceleration?

We use galaxy surveys to probe the fundamental physics of the universe, including understanding the driver of cosmic acceleration: dark energy. With our vast datasets of 100s of millions of galaxies, we confront core questions, such as how the universe formed and evolved. We use the galaxies' shapes to measure tiny coherent distortions (weak lensing) and positions to measure how clustered they are (clustering). I lead the weak lensing and clustering team within both DES and LSST DESC.

Image credit: NASA's Goddard Conceptual Image Lab

Are we seeing hints of non-standard dark matter?

Weak lensing is a unique cosmological probe because it provides unique access to relatively small scales of cosmic structure. On these scales, many dark matter models beyond the standard model could leave signatures. State-of-the art results from various cosmological probes have shown hints of differences in measures of how clumpy cosmic structure. There is tantalizing hope that this could be explained by new physics, such as a new model for dark matter. My group explores this.

Image credit: Ralf Kaehler/SLAC

Galaxy formation: Baryon feedback

Energetic processes in galaxies, like active galactic nuclei, have the power to eject baryons far from the center of galaxies, which can significantly impact the Universe’s small-scale matter distribution. These baryonic effects are poorly understood, which is a challenge for weak lensing cosmology, as it requires an accurate model for the Universe’s matter distribution. My group uses weak lensing, X-ray, and cosmic microwave background data to study these effects, and to compare to the state-of-the-art models and hydrodynamical simulations.

Dwarf galaxies: dark matter laboratories

One of our few windows to dark matter is the study of the

formation and evolution of galaxies, which are intimately tied to the growth of the dark matter `halos' in which they reside. Dwarf galaxies, like our own Magellanic Clouds, are 100x less massive than our own Milky Way, but they pack a dark matter punch! Compared to larger galaxies, they are dark matter-rich and comprised of only a small fraction of normal, luminous matter. We study their mass profiles -- how the mass is distributed radially from the galaxy center -- to test dark matter properties.

Estimating distances to 1 billion galaxies

At the heart of a weak lensing analysis is robust data calibration, which is challenging. My team has played a key role in developing new methodology that uses machine learning techniques to estimate the distances to galaxies based on their observed colours. This has been demonstrated within the Dark Energy Survey, and we are stress-testing it ahead of LSST.

How do galaxies align in the cosmic web?

Within our current understanding of galaxy formation, galaxies naturally align with each other and with the dark matter cosmic web, even in the absence of weak lensing. Understanding and being able to model the cosmic web is interesting, but these intrinsic alignment of galaxies are also a contaminant for a weak lensing signal. We group studies this effect to improve our analyses of cosmology.