Observational Cosmology

Large scale structure

Galaxies are not distributed uniformly in space, but cluster together tracing the large-scale structure of the Universe. This large-scale structure is itself shaped by the nature of the primordial perturbations, and the interplay of gravitational collapse and cosmic expansion through the history of the Universe.

We use large surveys operated from both ground-based and space-based observatories to map the positions of millions of galaxies. By analysing the clustering patterns in these datasets we uncover information about how the Universe has grown over billions of years, which we use to investigate questions such as the nature of dark energy. 

Galaxy survey projects we're involved in

• The Dark Energy Spectroscopic Instrument (DESI)

• Euclid 
• The Dark Energy Survey (DES) 
• The Extended Baryon Oscillation Spectroscopic Survey (eBOSS)
• The Baryon Oscillation Spectroscopic Survey (BOSS)

Gravitational lensing

Light doesn’t simply travel through the Universe in straight lines: its path can be bent by the gravitational effects of clumps of matter along its path. This deflection of light is called gravitational lensing and it can lead to both striking images of individual rare distant galaxies that have been stretched and magnified (known as “strong lensing”) and to much more subtle effects on the alignments of groups of galaxies (“weak lensing”) which can only be studied through statistical techniques applied to very large datasets.

At the ICG we study both strong and weak gravitational lensing. Our research reveals information on the contents of the Universe and the distribution of the dark matter which primarily causes lensing, on the nature of the source and lens galaxies, and even on the behaviour of gravity itself.

Gravitational lensing projects we are involved in

• Euclid 
• Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) 
• The Dark Energy Survey (DES)

Transients

Astrophysical transients are phenomena that appear suddenly in the night sky, brighten for days to months and then fade away and disappear again. This includes novae (eruptions on the surfaces of white dwarfs), supernovae (the explosions of stars), tidal disruption events (stars ripped apart by black holes), and the still mysterious gamma-ray bursts and fast radio bursts. At the ICG, we specialise in the study of supernovae and tidal disruption events.

Supernovae

 At the ICG, we focus on three areas of supernova studies: 

• Progenitors: understanding which stars explode as different types of supernovae and thus advancing our understanding of the life cycles of stars;
• Explosion physics: working out the details of how these explosions occur and the physics behind them; and
• Cosmology: some types of supernovae (famously, Type Ia supernovae that were used to first discover the accelerated expansion of the Universe) can be used to measure distances to their host galaxies and thus probe cosmology

Tidal disruption events

At the ICG, we work on discovering tidal disruption events (TDEs) in spectroscopic galaxy surveys (DESI, 4MOST) and studying the properties of the host galaxies of these events. This is an exciting new field of study, with plenty of open questions to pick from.

Transients projects we're involved in

• Dark Energy Survey (DES)
• Dark Energy Spectroscopic Instrument (DESI)
• 4-metre Multi-Object Spectroscopic Telescope (4MOST)
• Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST)
• Hubble Space Telescope surveys (BUFFALO, SIRAH)