My research uses observations of the Cosmic Microwave Background, combined with other tools such as the clustering and lensing of galaxies, to understand the contents and evolution of the Universe.

We think everything we see today came from a hot dense Big Bang, an extreme compression of space. As space expanded, tiny irregularities in a featureless universe evolved over billions of years to form cosmic structure, including galaxies, stars, and planets. 

The Universe only appears to be made of 5% normal matter, and I am trying to understand the missing 95%: Dark Energy and Dark Matter. I also want to understand the physics of the very early universe, to find out if ‘inflation’ happened, an extremely rapid expansion of the universe in the first trillionth of a second.

Science Oxford talk on Dark Universe, and interview clip.


Main research topics

Cosmic Microwave Background

Dark Energy and Dark Matter

Early universe, cosmic inflation

Galactic and extragalactic foregrounds

Atacama Cosmology Telescope (ACT) and ACTPol

The Atacama Cosmology Telescope (ACT) is a six-metre NSF-funded telescope in the Atacama Desert in Chile. From 2007-11 it measured the CMB anisotropy at arcminute scales over hundreds of square degrees of sky. ACTPol is the upgrade to ACT and had first light mid-2013. It is measuring the polarization of the CMB at small-scales, targeting neutrino and Dark Energy properties through gravitational lensing, and early universe physics through the primordial CMB signal.

These high resolution observations of the CMB signal from ACT have allowed us to better constrain cosmological models, and provide a window on new types of secondary measurements that allow us to probe the evolution of structure at late cosmic times. These include the Sunyaev-Zel’dovich effect as a probe of massive galaxy clusters, and gravitational lensing of the CMB by large-scale cosmic structure. At Oxford we work on modeling and interpretation of the data. 
Oxford team members: Dunkley, Louis, Calabrese, Naess, Allison

Discovery channel clip on ACT

ESA’s Planck satellite is the third generation CMB satellite, following COBE and WMAP. It launched in May 2009, and has now made full-sky observations of the CMB temperature and polarization anisotropies. It is allowing us to test theories of the early universe and better understand the origin of cosmic structure. Oxford team members: Dunkley, Calabrese, Armitage-Caplan.

The first Planck cosmology results were released in early 2013 and have given us a new estimate for the contents of the Universe and new evidence for inflation. Many extensions to the simple cosmological model have now been ruled out.  Measurements of distant galaxies have also shed light on when and where ancient stars formed in the early universe.

Planck data: Planck Legacy Archive, Early Release Compact Source Catalog

WMAP is a NASA satellite mission that launched in 2001 and measured the CMB anisotropy over the whole sky with high sensitivity, playing a key role in establishing the current cosmological model. I was a member of the Science Team since 2006, working on cosmological parameter estimation, as well as modeling and analysis of Galactic foregrounds. WMAP completed its 9th year of observations in 2010, and the final data analysis was completed late 2012. Oxford team member: Dunkley.

Nine-year data on LAMBDA:

Wilkinson Microwave Anisotropy Probe (WMAP)

In addition to analysis and interpretation work, I am also collaborating on a number of more theoretical projects connected to observations.

These include modeling the emission from high redshift star-forming galaxies, and modeling the Galactic magnetic field to predict polarized synchrotron and dust emission. I am also investigating how gravitational lensing of the CMB can be used to better understand Dark Energy. I also work on MCMC techniques for sampling high dimensional probability distributions, and other related statistical problems.

Theoretical work

The Planck satellite

Image courtesy the NASA/WMAP Science Team.

Image courtesy ESA, HFI and LFI consortia.

Image courtesy ESA, HFI and LFI consortia.

Credit: Sloan Digital Sky Survey Team, NASA, NSF, DOE.

Image courtesy ESA, HFI and LFI consortia.