James E. Taylor
Department of Physics and Astronomy
University of Waterloo
200 University Avenue West
Waterloo. Ontario Canada N2L 3G1
last updated Fall 2011
Tel. (519) 888-4567 x38115
Sec. (519) 888-4567 x32215
Fax (519) 746-8115
email: taylor [at] uwaterloo.ca
Current Research

Numerical Simulations of Dark Matter Halos
One of the ways we can learn about dark matter is by modelling how it should behave using numerical simulations. With the resources of SHARCNET, Ontario’s local supercomputing network, as well as machines in California, Germany and Australia, I have been studying how cosmology - the large-scale properties of the universe - affects the abundance, shape and smoothness of dense structures like galaxy clusters.
Studying this question together with Waterloo undergraduate Anson Wong, we have found that by measuring the shapes or concentrations of tens or hundreds of individual clusters, we may be able to distinguish between different cosmological models (cf. Wong & Taylor 2012). With M.Sc. student Uzair Hussain, I am trying to determine a practical way to implement these tests using data from gravitational lensing surveys such as the LoCuSS survey (see below). With M.Sc. student Jonathan Grossauer, I am looking at how the dense substructure inside dark matter halos (in clusters this would correspond to individual galaxies in the cluster) is stratified with age. The results of these simulations should help us understand the distribution of galaxies seen in the Next Generation Virgo Cluster Survey (see below). The simulations always seem to have more substructure than there are galaxies in clusters, particularly at the small (`dwarf’) end of the scale. With M.Sc. student Ryan Speller I am comparing the smallest substructure to distributions of faint companions around nearby galaxies (more on this below).
With graduate student Farbod Kamiab, I have also tried to determine how dark matter halos - the dense, roughly spherical structures that house galaxies and clusters of galaxies - merge together. This is a tough dynamical problem for which no good analytic solution exists, so we looked at simple merger simulations to understand the problem and develop better theory for it. The results of this work should help us understand how the Magellanic Clouds are interacting with the Milky Way, what happens when galaxy clusters merge together, and how smoothly dark matter is distributed in our own Solar System.
We see all sorts of amazing things in the Universe — other planets, other stars and galaxies — but the most amazing thing of all is how much we can’t see. More than 85% of the matter in the Universe is completely invisible to us; this is the mysterious “dark matter” you may have heard of.
I am using whatever tools I can, including numerical simulations, astrophysical theory and observational data, to try to figure what dark matter is, where it is, and how it behaves. My research includes gravitational lensing and dynamical studies of galaxy clusters, the properties of the smallest galaxies in the local universe, and the theory behind dark matter halos around galaxies and clusters.
I am an associate professor in the Department of Physics and Astronomy at the University of Waterloo in Waterloo, Canada. I am also an affiliate member of the Perimeter Institute for Theoretical Physics and a visitor at the Canadian Institute for Theoretical Astrophysics.
Observational Tests of Dark Matter
The COSMOS survey is a deep mosaic of images taken with the Advanced Camera for Surveys on the Hubble Space Telescope. It gives us a very deep view of a small patch of the sky (roughly 1.5 degrees on a side, the size of your fingertip held at arms length). Matter along this line of sight exerts gravity, bending light from the most distant galaxies as they pass by nearer ones. Measuring the shapes of millions of galaxies in the Hubble images, we were able to reconstruct the mass distribution in a thin pencil beam through the Universe. This provides tests of halo abundance and the evolution of structure with time.
I am now using the same data to constrain the dark energy content of the universe, by measuring the angular-diameter redshift relation. This small patch of the sky alone tells us that most of the energy content of the universe is dark energy
The LoCuSS Survey  is a targetted study of 100 massive clusters, selected to produce a very strong lensing signal. One of the goals of this survey is to measure the shapes of individual clusters and relate this to their formation history. It should provide direct tests of the simulations described above.
The Suprime Survey is a wide-are survey with the Japanese Subaru telescope to find clusters using gravitational lensing alone. This provides an important consistency check on our theory of structure formation, since such a survey should turn up any “dark clusters” not traced by luminous galaxies if they existed in the Universe.
COSMOS also provides a very rich data-set of galaxies imaged at many different wavelengths. I am searching through this field for small, nearby galaxies that trace
the dark matter distribution on the smallest scales. The relative abundance of these galaxies may tell us whether dark matter is genuinely “cold” (and thus lumpy on small scales) or whether it is “warm” (and thus fluffy on small scales).
To make further progress finding small galaxies, a shallow, wide-field survey is really preferable. With Waterloo undergraduate Kyle Johnston and postdoc David Gilbank I have made an initial search through data from the archive of the Canada-France-Hawaii Telescope. With MITACS summer student Arnab Dhabal and M.Sc. student Ryan Speller I am continuing this search, using a new filtering strategy to search for extended objects. The Next Generation Virgo Cluster Survey (Ferrarese et al. 2012) should also turn up many of these objects.
There are three main ways of studying dark matter observationally: galaxy dynamics, gravitational lensing, and direct or indirect detection of dark matter particles. I am currently involved in several large surveys that provide dynamical and lensing data, and I’ve previously worked on predictions for astro-particle experiments that search for the dark matter candidate particle (“direct detection”), or other particles it produces or interacts with (“indirect detection”).
Current Lensing Projects:
Galaxy Dynamics/Galaxy Surveys: