Cosmology with Galaxy Clusters (completed)
About the project
The study of galaxy clusters is among the central topics in modern astrophysics. In the era of ”precision cosmology”, with a range of different probes – including observations of high-redshift type Ia supernovae (SNIa), baryon acoustic oscillations (BAO), and the cosmic microwave back- ground (CMB) – providing strong evidence for an accelerating universe, with a well-constrained total dark matter density and present expansion rate, clusters of galaxies are still an important cosmological probe. Their growth from the highest density peaks in the early universe means that their mass function (the spatial number density of clusters of a given mass), particularly at the high-mass end, is extremely sensitive to the underlying cosmology. Furthermore, the dark matter distribution within the clusters is also a sensitive probe of the history of structure growth in the universe.
Primary objectives: A) Characterizing the physical properties of the new sample of galaxy clusters from the ESA Planck mission and derive resulting cosmological contraints and B) Use the detailed mass distribution in clusters to investigate and constrain various models that provide alternatives to dark energy, such as modified gravity.
Sub-goals: 1. Derive reliable photometric and/or spectroscopic redshift measurements for galaxy clusters discovered by Planck. 2. Make accurate gravitational lens measurements of the mass distribution in a set of galaxy clusters 3. Make accurate predictions of this mass distribution from N-body simulations in a range of different theoretical models that provide alternatives to standard LambdaCDM.
- Sub-project 1 The abundances of clusters: A significant large new data set of massive
galaxy clusters from the ESA Planck mission will be exploited to derive new
constraints on the evolution of cosmic structure as a function of redshift
and on the cosmological parameters that govern this evolution. Since the
Planck data do not carry any information about the distances to these
clusters, a large effort of follow-up observations using optical ground-based
telescopes will be undertaken to secure reliable photometric or spectroscopic
redshift data for all the clusters. Combined with additional follow-up weak
gravitational lensing and X-ray observations, the scaling relations between
cluster mass and baryonic observables will be derived, allowing the Planck
cluster sample to be used for cosmological constraints.
- Sub-project 2 The detailed structure of clusters: From detailed strong and weak
gravitational lensing measurements, the mass distribution can be derived
for a set of clusters. Similar constraints on the mass distribution will be
derived from simulated gravitational lensing observations of galaxy clusters
based on N-body simulations in a range of alternative dark energy models.
These models will then be tested by confronting the observations with the
simulated lensing data.
The project is funded by the Research Council of Norway and the University of Oslo for the period 2011-2013.
Sub-project 1: The Planck Working Group 5 organizes ∼20 scientists across Europe which are actively involved the SZ cluster science and other foreground science. Other members of the group provide strong expertise in the measurement of the SZ signal from the Planck data and theoretical modeling of the SZ cluster sample , and follow-up X-ray observations of galaxy clusters. The project manager of this proposal provides essential complementary expertise in optical/NIR observations, including weak gravitational lensing measurements.
Sub-project 2: Prof. Michael Gladders (at the University of Chicago, Department of Astronomy and Astrophysics and the Kavli Insititute for Cosmological Physics) is an expert on observations of galaxy clusters at a range of wavelengths and has pioneered methods for detecting high-redshift clusters in optical surveys, though the RCS and RCS2 surveys. His group also contain strong expertise on galaxy evolution.
The project is partially based on observational data collected at the Nordic Optical Telescope. The project also uses data from the ESA Planck mission the ESA XMM-Newton mission, the NASA/ESA Hubble Space Telescope, and data collected at the European Southern Observatory and the Subaru telescope.