An important step in understanding the nature of the universe, is simply to take stock of what's out there, and map where it is. We know that most of the matter in the universe is invisible dark matter, which so far we have detected only indirectly through gravity. Over the course of cosmic history, dark matter has clumped together under its own gravitational attraction, forming deep potential wells that eventually became the sites of galaxies and galaxy clusters. It seems that every galaxy and cluster lives inside a dark matter halo, and it is these invisible halos that I study.
There are several ways to measure the amount of dark matter in a halo, but gravitational lensing is unique in that it does not depend on assumptions about the dynamical state of the system (such as eg, Xray mass estimates, which rely on virial equilibrium). By far the most widely used lensing technique is called shear, and it looks at how shapes of background galaxies are deformed by the presence of a lot of dark matter along the line of sight.
In contrast, my research focuses on the magnification component of the lensing signal, and is complementary in many ways to the shear method. I measure magnification by looking at how number counts of background sources are altered by the presence of a halo. This is strictly statistical work, and I have to stack the signal from many tens to hundreds of galaxy clusters, to measure an overall average halo profile. Clusters of galaxies represent the most massive objects to have formed in the universe, and determining their total mass and density profiles is crucial to a comprehensive understanding of the cosmos.
For my PhD, I did a magnification analysis of a very large cluster sample in CFHTLenS (Canada-France-Hawaii Telescope Lensing Survey). The CFHTLenS is a huge deep survey, comprising about 154 square degrees on the sky, and containing over 18,000 detected galaxy cluster candidates. The large number statistics of this gravitational lens sample allowed me to ask all kinds of interesting science questions, and I explored the mass-richness relation, as well as the effects of cluster centroid offsets in that paper, which was published in 2014. As of 2014, we have made this catalog publicly available!
After completing the above magnification study, I followed up by investigating the shear signal of those same CFHTLenS clusters, as a comparison and cross-check on systematic effects. This recent comparison work yielded some very interesting comparisons, since we were able to explore effects as a function of different cluster attributes, making it an important step forward for the relatively new technique of cluster magnification. This CFHTLenS shear paper, and first direct shear-magnification cluster mass comparison, was published in early 2015.
The ultimate goal with magnification is to combine it in an optimal way with shear measurements, in an effort to have a less biased and systematic-influenced measure of lensing. In previous work, I looked at the magnification signal from a small sample of just 44 clusters in the COSMOS field, and found agreement between the cluster mass estimates determined by the two independent methods of shear and magnification.
See my Curriculum Vitae.
My notes on setting up a new MacBook Pro for astronomy and python development: Jes' Mac Setup.
Email me at: jesford@uw.edu