Dr Dodelson will focus on two issues central to understanding dark matter and dark energy: selection bias in measurements of weak gravitational lensing, and detecting the photons produced as dark matter particles annihilate. Galaxy surveys can include only objects above a given size and apparent brightness. When light from a background galaxy passes close to a dense region on its way to us, its light is bent ('lensed') so that it appears brighter and larger than otherwise. This bias introduces an illusory concentration of faint distant galaxies in the same parts of the sky as nearby concentrations of matter. A preliminary calculation shows that selection bias could change some measured quantities by as much as 10%. Dr Dodelson will undertake more detailed calculations, including an analysis of cosmological hydrodynamic simulations prepared for the Dark Energy Survey, and studies of how galaxy images are distinguished from those of stars in the Sloan Digital Sky Survey. His aim is to understand how selection bias is likely to affect future large surveys to measure dark energy with weak lensing, and to develop analysis methods that minimize it. Current ideas about the particles making up the dark matter predict that they should have finite lifetimes, so that gamma ray telescopes such as Fermi would detect thousands of photons produced when dark matter particles annihilate. However, the 'background' of gamma rays from our own Milky Way, and from the active nuclei of galaxies, is far brighter. Dr Dodelson will explore methods to extract the dark matter signal from the background.
A graduate student will be trained by participating in the research. Dr Dodelson plays a significant role in large collaborations including the Sloan Digital Sky Survey, the Dark Energy Survey, and the SuperNova Acceleration Probe, which aim at constraining the fundamental physics that gives rise to the dark energy.
