Description:
The standard model of cosmology, referred to as the ΛCDM model, predicts that dark energy (cosmological constant Λ) and dark matter (Cold Dark Matter) make up 95% of the universe, leaving only 5% composed of the ordinary matter so essential to our existence. The RENOIR cosmology team at CPPM focuses on the understanding of the history and composition of our universe, particularly in its dark components. The team has an expertise on supernovae (with SNLS/SNFactory and LSST projects), galaxy clustering (with BOSS/eBOSS, DESI and Euclid surveys) and the combination of cosmological probes.
In the area of precise cosmology, spectroscopic surveys of large-scale structures are one of the most powerful tools to extract cosmological parameters and to test modifications of General Relativity on cosmological scales. The Extended Baryon Oscillation Spectroscopic Survey (eBOSS) project is accumulating the largest 3D map of the Universe ever made, addressing fundamental questions in unexplored redshift regimes. Critically, the 1 < z < 2.2 expansion has never been probed using any method at comparable accuracy previously. The eBOSS survey, as part of the SDSS-IV program (2014-2019), will provide the observation of about 1.5 millions of galaxies. At CPPM we have the privileged access to SDSS-IV/eBOSS private data, before their public release for the astronomy community. The CPPM laboratory is also strongly involved in the preparation of the Euclid space mission, starting in 2020, that will measure shapes and redshifts of about 30 millions of galaxies out to redshifts ~2.
The candidate will focus on the application of the Alcock-Paczynski (AP) test on large spectroscopic surveys. The AP test is a pure geometric probe of the cosmic expansion history, which measures the shapes of objects that are known to be isotropic. Under an incorrect cosmology the shape of isotropic objects appears stretched/elongated in the line-of-sight direction. The AP cosmological test is so an evaluation of the ratio of observed angular size to radial/redshift size, constraining H(z)DA(z), where H is the Hubble parameter and DA is the angular diameter. The main advantage of this test is that it does not depend on the evolution of the galaxies, but only on the geometry of the universe. The PhD work will start by working on the galaxy clustering, including the AP test. Other potential application of the AP test consists of using the average shape of cosmic voids, expected to be spherical. This work will be done using eBOSS data.